PCB5235 - Exam 2

TCR Subtypes: Demographics in peripheral Blood

*Alpha-Beta T cell* -a-b gives specificity to this TCR -2:1 ratio of CD4 and CD8 in periphery -60% CD4+ and 30% CD8+ -very few are double positive or double negative -indicates health -differences in number indicates problems -Ligands = MHC and peptide antigens -LARGE repertoire of germline genes dedicated to making these TCR -have construct to limit them from reacting to wrong thing *Gamma-Delta T cell* -g and d chains provide specificity -THIS g-d associates with specificity (other g-d are components for TCR complexes) -still has z-z, g-e, and accessory molecules in TCR complex -g-d T cells are FEWER in Peripheral blood -very few CD4+ -MOSTLY CD8+ at 30% -60% are CD4 and CD8 Double Negative in peripheral blood -if majority of g-d cells are double negative, majority of g-d T cells are *NOT MHC restricted* -do not need to interact with MHC for signal transduction -many g-d cells do not interact with proteins, but phospholipids -TCRs recognize phospholipids and intact/whole proteins -do NOT see pieces in context of MHC I or II -Ligand = phospholipids and proteins -small repertoire of germline gens to make g-d TCRs -limits them to interacting with random phospholipids -*giver higher chance of autoimmunity* -Smaller repertoire = greater chance of recognizing self because they are not as restricted -g-d T cells serve as boundary guards -parts where body interacts with outside world (certain proteins associated with different organisms) -get whole process of destroying those things if they go from outside to inside -have specific TCR for this action -BUT are more LIMITED in what they can recognize in order to help recognize things that are more common, but in specific manner (they are specific for common things)

B Cell Development

*Antigen Independent* -within Bone Marrow -progenitor B cell becomes more terminally differentiated (has CD45R/B220) -moving towards becoming B cell, but does not have BCR -CHANGES DNA within B cell to cause formation of BCR -Form BCR -every B cell has own BCR -selection process to ensure B cell recognizes something -B cells tend to be more self-reactive than T cells -something happens in periphery to make sure B cell does not react to self -B cell travels into periphery when ready -is naive B cell (leaves bone marrow) -does not form proper BCR, undergoes PCD in periphery *Antigen-Dependent* -enters lymph node/ secondary organ/ B cell follicle -B cell is specific to antigen before going into follicle -antigen and activated B cells condense within lymph node -Follicular DC (FDC) has Fc region to bind to antibody -FDC binds antibodies of activated B cells -specific antigen then binds to bound antibody on FDC -FDC acts like APC (not real APC), and activates Follicular Helper T Cell (TFH) in follicle -TFH activates naive B cells -naive B cells may rearrange BCR to be more specific to an antigen -activated B cells are tested by FDC -High affinity B cells that bind to antigen on FDC outcompete Low affinity B cells -High affinity = Ka2 -*Ka2 is better than Ka1* for best binding -Activated B cells become Plasma or Memory B cell

Maintaining Homeostasis through Programmed Cell Death (PCD)

*Apoptosis* -morphologic changes associated with programmed cell death -includes Nuclear Fragmentation, Blebbing, Release of Apoptotic Bodies Prevents release of intracellular contents such as proteolytic enzymes, cationic proteins, and oxidizing molecules -prevents erratic danger signals/unnecessary DAMPs Leukocytes have fixed lifespan and die by PCD -5x10^10 Neutrophils in circulation, alive for 1 day PCD used by CTLs and NKCs to kill target cells *Necrosis* -cell swells up and bursts -unplanned/NOT good -OPPOSITE of apoptosis Lupus =disease where people cannot clear debris from PCD -Macs supposed to be specialized everywhere to clean up debris

Stem Cell Transplantation

*Autologous* -take out own stem cells, bank them, and put them back in -Self-Transplant *Syngeneic* -mice with identical genetic makeup/ identical twins *Allogeneic* -taking stem cells from different person and putting into unrelated patient *Graft vs Host Disease* GVHD -can occur in these transplants -requires immunosuppression so stem cells don't attack the host (opens problems for other infections to occur) -if host cells attack stem cells, is transplant rejection

BCR/TCR Required for Activation

*BCR*: -disulfide bonds help to maintain structural integrity -immunoglobulin folds start to present a certain type of structure -mIGM: membrane form IgM -IgM is isotype of antibody or BCR -1st antibody that begins to form, because that is the one the B cell develops in high frequency -B cell membrane bound IgM -when interacting with antigen, Light and Heavy chains BOTH contribute to binding interaction with antigen -Heavy: largely part of what the antibody does when membrane bound (turns B cell on) -VL/VH = variable light/heavy -part that changes so it can interact with different types of antigen -CL/CH = constant light/heavy -part of chain that doesn't really change -constant region still has different isotypes -Cmu = constant M / constant membrane isotype *TCR*: -alpha-beta is MOST COMMON form of TCR -alpha chain and beta chain -Gamma-delta TCR also exists -has gamma chain and delta chain -Immunoglobulin folds = disulfide bonds that provide structure -In context of MHC = variable region -encounter antigen in context of MHC, responds to antigen or makes proteins -T cells have to touch the antigen (T cell has to move for TCR to make contact) -BCRs can become antibodies by removing antibodies form membrane, can find antigen, and come back -means T cells have to be self-sufficient -CD4 and CD8 also interact with MHC to help drive response -Constant region: stays similar

Quiz 4: Which of the following inhibits apoptosis?

*Bcl-2* -inhibits apoptosis of T cells, as long as antigen is present *Fas* -located on target cells -INDUCES apoptosis by INITIATING it *Caspase* -several types -protease -PROMOTES apoptosis *Bax* -opposes Bcl-2 -PROMOTES apoptosis

*MEMORIZE* Apoptosis Regulation Via Genes

*Bcl-2* -PREVENTS / INHIBITS apoptosis, in response to presence of antigen *Bax* -opposes Bcl-2 and PROMOTES apoptosis *Caspase* -several types -protease that PROMOTES apoptosis *Fas* -located on target cells -INDUCES apoptosis by INITIATING it

T Cell Regulation

*CTLA4* -competes with CD28, binds B7.1 and B7.2 interactions -protein receptor expressed on many regulatory T cells (Tregs) -causes an *inhibitory* signal that shuts down the cell *(IS AN ITIM)* *Cytokine Signaling Suppressors* Include: -Immunomodulatory Cytokines (ex. IL-10) -PD-1 Ligands (programmed cell death-1) -inhibits activation and induces apoptosis -Regulatory T cells (Tregs) *Apoptosis in absence of continued TCR stimulation* *Can also regulate the receptor on the cell itself, so it does not respond to cytokines around*

Essential Transcription Factors

*GATA-1* -Erythroid lineage *Bmi-1* (bone marrow induced-1) -ALL hematopoietic cells/lineages *Ikaros* -Lymphoid lineage

Hematopoiesis of Natural Killer (NK) and Innate Lymphoid (IL) Cells

*Innate Lymphoid Cells* (ILCs) -bridge gap between innate and adaptive immune response -TCR differs between ILCs and Adaptive Cells (ILC TCR is broad, Adaptive Cell TCR has specific cytokines) Lymphoid Tissue Inducer (LTI) -lymphoid cells reside within lymph nodes ILC Precursor: *ILC1* -Transcription factor = *T-bet* -T-bet promotes/helps to promote production of *IFNgamma* -helps gear immune response towards fighting something INTRAcellular (adaptive side attacks EXTRAcellular with antibodies) *ILC2* -Transcription factor = *GATA3* -*IL-4* production, which helps B cell make antibodies *ILC3* -Transcription factor = *RORgammat* -allows commensals to stay -eliminates pathogens -look like T8 17s (phenotype not terminally stable) -can begin to make T-bet again (looks like TH 1)

Gut-Associated Lymphoid Tissue (GALT)

*M Cells* -separate internal and external environment -part of Peyer's Patch, NOT the entire patch -take inventory of things within the gut -make sure commensals are there, and bad bacteria are outside *Interepithelial Cells* -one of the goals of Innate Immune System is to keep problems outside, so body doesn't have an immune response -GALT is one thing that keeps bacteria away from "inside" -some bacteria are important in regulating and forming functions for the body -there are good and bad bacteria *Peyer's Patch* -villi push things from mouth down to the end -M cells do NOT have villi, so they have chance to sample what comes into the gut -Interepithelial cells are Innate Lymphocytes that begin to release some cytokines, but lack TCR -has GC to make B cells for microorganisms being sampled -cells come in from blood through HEV -lymphocytes go into the lymph vessels -antigen goes into Peyer's Patch -Helper T cell, B cells, Macs, and M cells make controlled situation of screening antigen and taking are of it -Lumen = outside of body/GALT -Intraepithelial Lymphocytes - between lamina propria and Endothelial cells -Plasma and B cells produce antibodies -make IgA (generally dimeric or more) -NOT generating inflammatory response based on those antigens -NO inflammatory response because IgA Fc regions DO NOT interact with Fc receptor or complement -IgA goes into lumen (IgA bind to bacteria, and push them along so homeostasis is maintained, and so bacteria don't stay long)

Humoral Response: Naive vs Memory

*Naive*/ *Primary* -Lag period after antigen = 4-7 days -Time of peak response = 7-10 days -Magnitude of peak antibody response = Varies, depending on antigen -Antibody isotype = IgM in early primary response -Antigens = Thymus independent and Thymus dependent -Antibody affinity = LOW -Lifespan of cells = short lived/ days to weeks -Recirculation = yes *Memory*/ *Secondary* -Lag period after antigen = 1-3 days -Time of peak response = 3-5 days -Magnitude of peak antibody response = 10-1000x higher than primary response -Antibody isotype = IgG predominates (IgA in mucosal tissues) -Antigens = primarily Thymus dependent -Antibody affinity = HIGH -Lifespan of cells = long-lived, up to lifespan of animal host -Recirculation = yes

Apoptosis vs Necrosis

*Necrosis* -signifies danger (something happens in uncontrolled fashion) What happens: -chromatin clumping -swollen organelles -flocculent mitochondria -Disintegration = release of intracellular contents (triggers inflammation) *Apoptosis* -NORMAL, daily process of cells -CTLs/NKCs HELP cells that have problems to undergo apoptosis -NOT mounting significant immune response to something that is natural What happens: -mold convolution -chromatic compaction an segregation -condensation of cytoplasm -nuclear fragmentation -blebbing -apoptotic bodies -Phagocytosis = apoptotic bodies taken in by phagocytic cell

Antibody Functions

*Neutralization of virus infectivity* -viruses treated with specific antibody lose their ability to infect cells in vitro and to infect animals *Neutralization of toxins* *Opsonization* -coating of bacteria with antibodies -or Ab+ complement increases rate of phagocytosis *Activation of complement* *Antibody Dependent Cell Cytotoxicity (ADCC)* -in NKCs Antibody variable (Fab) and constant (Fc) region neutralizes, coats, or activates

Quiz 4: Which of the following has the shortest lifespan?

*Neutrophil* ~1 day *Red Blood Cells* ~120 days *T Lymphocytes* ~20-30 years or whole lifespan

Organs of the Immune System

*Primary Organs* -where lymphocytes reach functional maturity -Bone marrow, thymus (humans and mice) -T cell progenitors made in bone marrow, but functional maturity where they get TCR happens in thymus *Secondary Organs* -where mature lymphocytes interact with antigens -lymph nodes, spleen, MALT, GALT -T and B cells form maturity first, then move elsewhere to interact with antigen *Lymphatic System* -how antigens interact with T cells -network of vessels that collect fluid/lymph that escaped tissues from circulatory system, and return it back into blood

Stages of Adaptive Immune Response

*Recognition* Day 0 -detect antigen *Activation* Day 7 -clonal expansion of B and T cells *Effector Phase* Day 14 -antigen removal, immune cells work -release cytokines, apoptosis of bad cells/pathogens -good clearance of pathogens *Decline* Roughly Day 20 -Immune cell apoptosis -don't want cells persisting, or the body will be harmed *Memory* >30 Days (varies for antigen) -some immune cells remain for repeat exposure -some cells last for a lifetime

Signaling Overview: Background for Activation

*Signal Reception* -signal binds to receptor -protein-protein molecular interactions drive some sort of response -Hoe interactions occur: ~*Membrane Bound Signals*: one is a ligand, and one is a receptor on membrane surface ~*Water Soluble Ligand*: Cytokines - need receptor to understand ~*Membrane Soluble Ligand*: Able to pass phospholipid bilayer/ steroids do this *Transduction* -conformation change when ligand binds -ligands tend to have charges: conformational changes happen -Different charges interact and induces change in order to balance really strong charge from ligand -usually exposed an area where something else can bind -may also have cleavage event that exposes site for binding -conformational change allows certain docking sites to open, which allows certain molecules to bind -binding may include more site opening to bind -secondary molecules may then interact with new structures -phosphorylation or dephosphorylation events -secondary molecule drive most of the signal cascade within cell signaling -signal cascade means signal grows larger -may then go to nuclear to produce specific proteins or other changes

Principle facets of the Adaptive Immune Response

*Specificity* -different cells mediate specific responses *Diversity* -immune system is capable of responding to large numbers of microbes *Memory* -able to recall previous encounters with antigens -leads to faster, stronger response to future encounters with same microbes *Optimization* -able to specialize attacks for distinct microorganisms *Self-limiting* -capable of starting and stopping an attack of a new organism *Safe to Self* -does not accidentally attack self tissues

Quiz 5: Describe both B and T cell development, noting important stages and locations.

*T cell* -T cell precursor produced in the bone marrow -reach full maturity in Thymus by gaining TCR -cortical region of thymus, T cell becomes double positive for CD4 and CD8 -cortical epithelial cells in cortex present antigen, helping T cell become single positive to CD4 or CD8 -T cell exposed to Promiscuous Proteins in periphery to be educated to detect "non-self" -gene AIRE promotes expression of proteins in thymus to recognize "non-self" -tests to see if mature T cells function properly -most do not, and 95% of thymocytes die by apoptosis *B cell* -B lymphocytes produced and mature in bone marrow -B cell rapidly proliferate and undergo isotype switching and somatic hypermutations within germinal centers (GCs) of secondary follicles of lymph nodes -Antigen-Independent Phase: -progenitor B cells become more terminally differentiated -undergo actual DNA change/Ig-gene rearrangement to cause formation of BCR -once they become a mature B cell by gaining BCR, leave bone marrow and go into peripheral lymphoid organ -Antigen-Dependent Phase -Mature/Naive B cells go through selection process to ensure BCR does not react to self -peripheral lymphoid organ, aka secondary lymphoid organ, where naive B cells reside within lymph nodes -activated B cells and antigen concentrate in lymph node -Follicular DCs (FDCs) take up the antigen and present it to activate Follicular T Helper Cells (TFH) -TFH then activate naive B cells to recognize a specific antigen and produce antibodies for them -FDCs have an Fc receptor that binds to Fc region of antibodies specific to incoming antigen -antigen bind to antibodies, which are bound on FDCs -FDCs screen activated B cells by having them bind to presented antigen -ensures High Affinity B cells pass, and Low Affinity/Self Recognizing B cells go through programmed cell death

CD4 (TH) Cell Subtypes: Commonly Produced Chemicals

*TH1* -IFNgamma -targets intracellular pathogens -interferes with viruses or bacteria INSIDE of a cell *TH2* -IL-4 -targets extracellular pathogens -helps guide effector functions of B cells, or guide isotype switching *TH17* -IL-17 -target extracellular pathogens/ fungi -has many different types/isoforms -plays tole in going against fungal infections, and depicting between friend vs foe/ regulating bacteria in gut *TFH* -important in humoral immunity and B cell development in GC in secondary lymphoid follicles -TH2 and TH17 also important in humoral immunity because they help B cell communication but MAIN thing is location -TFH are INSIDE follicle to help drive expansion and differentiation

Stem Cell Types

*Totipotent* -give rise to ANY cell in an organism -can essentially give rise to an entire organism *Pluripotent* -give rise to most, not all cell types -HSCs -Embryonic stem cells *Multipotent* -give rise to limited number of cell types *Unipotent* -only replicate themselves

Thymus

-Bi-lobed organ where each lobe is divided into lobules (separated by trabeculae) Purpose: -generate T cell repertoire that will protect from infection -where T cells mature and most die (PCD because unable to recognize MHC complexes when trying to generate TCR) Thymocytes of thymus undergo gene rearrangement -produces enormous diversity of TCR -most fail to recognize MHC-Antigen complexes -some capable of mounting immune response to self = BAD -more than 95% of thymocytes due by apoptosis Role of thymus can be studied in thymectomized mice/nude mice with DiGeorge's Syndrome Decrease in size with age (function in thymus decreases with age) -30g in infants, 3g in elderly -20% output of newborn same as full output at 35 -2% output of newborn at 65 -young have immune system that is starting to form -elderly not producing same amount of T cells (hopefully have memory cells to fight, but don't have same amount of output from clonal expansion)

T cell Development

-T cell progenitor leaves bone marrow, follows cytokines/chemokines to proteins -THEN goes to thymus -is a *Double Negative* -cortical region of thymus, where it becomes *Double Positive* -gains BOTH CD4 and CD8 -Cortical Region = has cortical epithelial cells -important in presenting antigen when get TCR for either CD4 or CD8 to become single positive -in development of TCR to interact with MHC I or II, to become *Single Positive* (gene that gets positive stimulation/feedback is the one the T cell becomes - whichever interacts first) -Trying to educate T cells to ONLY respond to non-self -proteins get presented in periphery to educate T cells early on -Promiscuous Protein expresses "non-self" to educate -Gene AIRE promotes expression of proteins in thymus to recognize non-self -TCR develop, and tested to see if it functions with AIRE -no correct function, dies by apoptosis PROCESS: -double negative (DN) when when entering thymus -DN in subscapular cortex -double positive (DP) in cortex -becomes single positive (SP) in cortex -SP moves through cortical medullary junction (CMJ) into medulla -SP then exits thymus

Natural Killer T Cells (NKT Cells)

-characteristics of both T and NK Cells -have TCRs -TCR does NOT recognize peptides like normal, but instead sees CD1 and glycolipids (activated by things in environment, not peptide) -Interacts with MHC-related CD1 (non-peptide), glycolipids -express CD16 (Fc receptor binds to antibody) -used in Antibody-Dependent Cell -Mediated Cytotoxicity (ADCC) -Can secret large amounts of cytokines for: ~supporting antibody production ~inflammation of cytotoxic T cells

Quiz 4: Theoretically, what is the fewest number of enriched HSCs needed to reconstitute a mouse?

1

Quiz 4: Nuclear fragmentation and blebbing are associated with ___ while cell swelling and bursting is associated with ___.

1) Apoptosis 2) Necrosis

B cell Activation: T-independent 2

2 signals 1) signal from antigen 2) CD21 which has ITAM C3d -complement component 3 desarg -lacks an arginine, different from typical complement -opsonizes the antigen (opsonized pieces float until they bind to BCR and activate B cells) T-independent because T cell activation often requires more -B cell bridge gap to buy us more time

Quiz 4: Go through the process of HSC isolation and enrichment. Be sure to use relevant vocabulary in your explanation.

A person or animal's body is irradiated to get rid of cancerous/unhealthy cells, and to prepare the body for stem cell transplant to minimize transplant rejection. Stem cells are isolated from a donor. They usually come from long bones, but peripheral blood is sufficient to get HSCs. *HSCs* are stem cells that have not undergone differentiation, which means they do not have proteins/antigens on their surface to distinguish from other cells. *Panning* is an isolation method. A plate is coated with antibodies specific for cells that would be found in peripheral blood. These cells will bind to the antibodies on the plate, and HSCs will NOT binds. *Unbound cells* are taken from the plate, They are then examined to ensure they are HSCs and that they are healthy. Isolated HSCs then injected into irradiated subject. HSCs are able to proliferate quickly and reconstitute an irradiated immune system. Many HSCs/fully enriched dose of cells injected into patient, reconstitution would occur quickly. Due to how quickly HSCs can divide, one is enough to reconstitute and enrich one's weak or nonexistent immune system.

Reconstitution

Absence of HSCs, can't make RBCs or WBCs -animals/people will die -animal/human is lethally irradiated and HSC is added to reconstitute *Unenriched Cells* -restores hematopoiesis and mouse lives -needs A LOT of unenriched cells (no HSC) for mouse to live Even if we don't have complete immune system, we can still survive (presented by graph) *Partly Enriched Cells* -few HSCs injected -few cells are enough to restore hematopoiesis and mouse lives *Fully Enriched Cells* -many HSCs -only FEW HSCs needed to let mouse live because HSCs divide quickly -a lot of HSCs reconstitutes immune system quickly

Naive T cells Require Co-stimulation for Activation, or Anergy Occurs

Activate Naive T cells with DCs -high levels of costimulatory molecules that give them enough signals, signal transduction cascade to them activated APC -must be professional APC with C7 APC with Naive T cell: *2 signals transduced* 1) Costimulatory molecules -B7/CD80/CD86 interact with CD28 -DC is IMPORTANT in activating Naive T cells 2) Antigen-MHC-TCR Complex -signals help promote upregulation of IL-2 and IL-2 receptor IL-2 helps drive activation of T cell -causes cell to go into cell cycle -starts cell division and clonal selection of memory and effector cells -need BOTH signals for this to happen -if only 1 signal, will be functionally turned off -*No co-stimulation results in Anergy* -T cell needs to be REALLY regulated in what they respond to No co-stimulation/ No B7 interaction with CD28 -*Anergy occurs and T cell NEVER reacts to anything within it's lifetime* -once cell is anergized, can never be clonally expanded in the future

HSC Isolation, Enrichment

All cell types have unique proteins on surface that distinguishes from other cells -liver cells have liver specific proteins/antigens -CD4+ T cells have specific proteins on surface HSCs haven't undergone differentiation, so they do NOT have some proteins on surface -HSCs LACK unique proteins on surface to distinguish from others Antibodies specific for markers on mature cells at various differentiation stages (ex. RBCs and WBCs) are added -separate HSCs by tagging with antibodies -all cells tagged EXCEPT HSCs Labeled cells removed by "panning" or FACS (Fluorescence Activated Cell Sorter) -both follow negative selection -what is NOT tagged is HSC Small amounts of remaining cells/ non-tagged are used to reconstitute irradiated humans/mice/animals

Panning

Antibodies are specific to proteins on specific cell types Takes cells and put them on the plate coated with antibodies -cells bind to their respective antibodies Leaves HSCs alone with no proteins -taken and analyzed, and used to reconstitute

Spleen: Antigen Migration

Antigen enters through the *splenic artery* -empties into *marginal zone* Antigen is trapped in marginal zone by DCs -DCs process antigen -DCs move to PALS In PALS, DCs present antigen on MHC II to naive CD4+ T cells -results in T cell activation within spleen Loss of spleen results in bacterial sepsis in children

Antigen Migration in the Lymph Nodes

Antigen get trapped within Paracortex -DCs internalize, process, and express antigen on MHC II to Helper T cells -upregulation of CD80 and CD86 *important* in activating Naive T cells -soluble antigens bond to BCR specific to antigen B and T cells begin forming "foci" -clonal colony specific to antigen -4-6 days: some plasma cells produced -4-7 days: some B cells and TFHs migrate to primary follicles in cortex (or to secondary follicle with GC for rapid cell division) (GC is where affinity maturation for Plasma Cells occurs)

Antigens

Antigens = anything that elicits an immune response USUALLY foreign -except in autoimmune diseases -Multiple Sclerosis = destruction of myeloid sheath -Rheumatoid Arthritis = inflammation of the joint Antigens can be: -High molecular weight compounds (>5 kDa) -Low molecular weight compounds (Haptens) -attached to large molecular weight compounds -a lot of immunology has been learned through Haptens

Lymphatic System: Movement of Lymph

As blood travels under pressure, plasma seeps through thin capillary walls into surrounding tissues -up to 2.9L of interstitial fluid is generated in adults per day, which bathes tissues and cells -fluid eventually returns to blood -if fluid does not return to blood, swelling/Edema can occur, which can be life threatening Most fluid is returned back to blood through walls of the venules -remainder passes through primary lymphatic vessels -cells (Macs, DCs, lymphocytes) can ALSO PASS through thin wall Thoracic duct empties into left subclavian vein -Thoracic Duct is largest lymphatic vessel Muscle contractions help move lymph in a unidirectional path -Unidirectional movement of Lymphatic System keeps process going in continuous cycle

High Endothelial Venule (HEV)

B cells are generated in Bone Marrow and Spleen They GET INTO lymph nodes through HEV, form blood -they get into the blood through HEV -lymph nodes get things from lymphatic system and the blood Efferent = outgoing lymph vessel Has antibodies and 50x more lymphocytes -mostly from migration of blood-borne lymphocytes (some due to proliferation) Most antibodies and lymphocytes are coming in through Blood and HEV -Efferent mostly made of lymphocytes from blood Blood-borne lymphocytes migrate though capillary venule using HEV *Extravasation* - migration of cells through HEV *HEV are NOT just present in lymph nodes* HEV allows cells to extravasate into lymph tissue from blood

Regulatory T cells (Tregs)

Basic goal of immune system is not only defense against infectious microorganisms, but also *tolerance to self* Tregs play active role in tolerance -absence of Tregs = autoimmune diseases develop Tregs require TCR stimulation for activation -HOWEVER, instead of promoting an immune response, they *shut them down* -part of checks and balances system to prevent autoimmunity Often have affinity for self-antigens Types (many types of Tregs in body) -majority are CD4+, some are CD8+ -many different mechanisms in which Tregs interact -*TR1* -Isolation via: culturing CD4+ T cells in presence of IL-10 and antigen -Suppression: produces IL-10, TGF-beta, and IL-5 -*TH3* -Isolation via: low dose oral antigen -Suppression: produces TGF-beta and IL-10 -*CD8+ Tregs* -Suppression mechanisms vary between systems ~can be contact dependent or independent ~*Contact Dependent* = makes IL-10 to inhibit ~*Contact Independent* = other signals -*CD4- CD8- (Double Negative) Tregs* -suppression is contact dependent -*Naturally occurring CD4+ and CD25+ (double positive) Tregs* -CD25 = IL-2 receptor, alpha chain -already have IL-2 receptor present, and IL-2 is important for clonal expansion -Tregs act like sponge and soak up all the IL-2, so other cells do not activate and go into clonal expansion -constitutes 5-10% and 2-4% of peripheral CD4+ T cells in mice and humans respectively -possess TF *Foxp3* -important for making the cell do what they do -master transcription factor -possess CTLA4 receptor -CD28 competitor -CTLA4 provides inhibitory signal, interception costimulatory signal to stop activation

Immune Cell Division of Naive B Lymphocyte

Becomes activated/ gets BCR -enters cell cycle -cell cycle regulated by specific receptors Mitosis occurs -are terminally differentiated, becoming Memory or Effector Cells -go back into G0

Quiz 5: Which of the following is not considered a secondary lymphoid organ?

Bone marrow *Primary Organ* -where B lymphocytes reach functional maturity *Secondary Lymphoid Organ* -lymph nodes -spleen -GALT -MALT

Classical Hematopoiesis Overview

Can become *Common Myeloid Progenitor* (CMP) or *Common Lymphoid Progenitor* (CLP) *CLP* -B lymphocytes -T lymphocytes -Natural Killer *CMP* ~Can Self Renew: -Erythroid CFU -Megakaryocyte -Basophil CFU -Eosinophil CFU -Granulocyte-monocyte CFU ~Cannot Self Renew: -Erythrocytes -Platelets (made by Mega) -Basophils -Eosinophils -Neutrophils (made by Granulo) -Monocytes (made by Granulo) Differentiation: -transcription factor made -changes proteins made -changes proteins expressed on surface (environment causes changed in what a cell can make and do, which causes differentiation in a particular area and be more specific) Hematopoietic Cytokines: -Generated by Macs, Stromal Cells, and Activated T cells

T Cell Subtypes

Common Lymphoid Progenitor (CLP) -make NK, B, and T cells T makes T Helper or T Cytolytic Cell T Helper makes TH1, TH2, Treg, or TH17

DiGeorge's Syndrome Patients

Deletion of small segment of chromosome 22 -symptoms vary, but often has heart problems, specific facial features, frequent infections, developmental delay, learning problems, and cleft palate -includes T cell deficiency Susceptible to *intracellular* pathogens because T cells recognize antigens, cancers, and virally infected cells -also susceptible to *extracellular* pathogens because DCs present antigens to T cells If you knock out the T cells, you knock out the adaptive -leaves innate response to largely work/function to fight infections

Regulation at Genetic Level of Hematopoiesis

Developing HSC into cell types requires expression of different genes are correct time -regulated by various transcription factors (TFs) TFs regulate proteins, which regulate what cells do -TFs drive particular part of phenotype (TF gone, phenotype will be gone) -Test TF hypothesis by getting rid of the proteins the TFs make -job it does should no longer occur, which means protein that does the job is not made MOST of what we know about the role of TFs in hematopoiesis comes from *knockout (KO) mice* -knockout TFs to see what function TF has (looking to see what job is not done when TF is gone - that is TF's job)

B cell Activation: T-independent 1

Don't need T cells to activate BCRs on surface -interact with cilia on bacteria -BCR specific for something common on bacteria Toll Like Receptors (TLRs) -recognize something that is specific to bacteria 2 signals to become activate: 1)signal from BCR 2) signal from TLR B cell still needs T cell for Isotype switching -but gets activated in response to bacteria, in absence of T cells -good for quick response to something common Good at activating complement -drive clearance of bacteria before Adaptive Immune Response Occurs (which takes some time)

Apoptosis in Lymphocyte Populations

During infection, lymphocytes are clonally expanded and grow/count increases 4-fold -NOT around forever (unneeded lymphocytes are eliminated) TF Bcl-2 INHIBITS apoptosis -activated lymphocytes have decreased levels of Bcl-2, in comparison to naive lymphocytes or memory cells (means activated cells are MORE susceptible to apoptosis) -as long as antigen is present, Bcl-2 is present -continued antigen presence blocks apoptotic signal (more antigen = more Bcl-2 present) -once initiating event/antigen is gone, Bcl-2 will decrease, and apoptosis of T cells will occur (attack NO LONGER NEEDED) -less antigen = less Bcl-2, apoptosis occurs

Hematopoietic Homeostasis (HH)

Dynamic equilibrium: cell lifespan/concentration differs for equilibrium RBCS -lifespan = 120 days, before Macs phagocytose and digest them in spleen -spleen is important in immune response and cleaning up RBCs -RBCS able to bind glucose (determine how much glucose present in person in period 4 months/ 120 days) (can see if glucose stuck to RBCs go up or down) -HH used to understand biological condition of diabetes Neutrophils -lifespan = 1 day Some T Lymphocytes -lifespan = 20-30 years, of even lifespan of person -*IMPORTANT* memory T cells have quick response against antigen Humans make ~3.7x10^11 WBCs per day Many factors: -cytokines are main thing contributing to maintenance of HH

Quiz 5: Which of the following pathogens poses a greater threat to children with the loss of the spleen?

E. coli (loss of spleen results in increase of *bacterial sepsis* in children) Not bacteria: -plasmodium falciparum -rhinovirus -influenza

Lymph Nodes

Encapsulated bean-shaped structures Full of Lymphocytes, DCs, Macs First organized lymphoid structure to encounter antigens entering tissue spaces -antigens become trapped for antigen presentation Cortex = B cells, FDCs, TFH, Macs -present in BOTH primary and secondary follicles GC located within cortex -ONLY secondary follicles Paracortex = B and T ells, DCs -presenting MHC II -where B cells interact with antigen to become activated Medulla = sparse lymphocytes, antibody-secreting plasma cells -mature B cells that make antibody are present

Quiz 5: Secondary organs are where lymphocytes reach functional maturity. True/False

False *Primary Organs* -where lymphocytes reach functional maturity -B in bone marrow, T in thymus *Secondary Organs* -where mature lymphocytes interact with antigens -lymph nodes, spleen, MALT, GALT

Quiz 5: The left subclavian vein is the largest lymphatic vessel. True/False

False The thoracic duct is the largest lymphatic vessel

Quiz 4: Hematopoietic Stem Cells are difficult to study because they are rare and cannot be cultured. True/False

False They are difficult to culture, but nevertheless can be cultured in certain situations

Hematopoietic Activity Over Time

Fetal: -yolk sac -liver and spleen Adult: -cranium, pelvis, sternum, ribs, vertebrae (grow throughout most of old age) -hematopoietic activity mainly in bone marrow (also in other places of body)

Cartoon Video of B Cell Activation in Germinal Center

GC = where B cells proliferate and undergo isotype switching and somatic hypermutations -Isotype switching = allows antibodies different jobs -Somatic Mutations = mutation in receptor to have different specificities to antigen GC forms within B cell follicles in Lymphoid Organs -formation of GC starts when FDC displays antigen on surface to activate CD4+ T cells -CD4+ T cell proliferate and mature into Effector Cell/ Helper T cells -capable of activating antigen specific B cells -B cells proliferate to form primary focus on antigen specific B cells -other B cells from primary focus persist in T cell area for a short while to make antibody, but eventually die -B cells that entered follicle proliferate rapidly -also undergo somatic mutations to introduce new variation into BCR -B cells undergo process of selection after somatic mutation -BCR tested for ability to bind antigen on FDC -those that fail to bind or fail to compete against high affinity B cells die

"Immunology in Galt" Video

Gut is body's first contact with microbes -when ingested, microbes go to mucosa in gut -most die in acidic environment of stomach -some strong enough to go to intestines (villi of small intestines) -small intestine has clear spots/patches of lymphoid tissue: *Peyer's Patch* -villi and lymphoid tissue go to mesenteric lymph nodes to act as important barrier from microbial invasion -patches have M cells, which help separate between good and bad cells -IL-10 is important in gut -prevents inflammation -Neutrophils important in getting rid of unwanted microbes -they can also cause damage to tissues because of the release of microbial cellular contents *There is a balance between inflammation and tolerance* -default is tolerance because we cannot always have inflammation *Noted in Video* -Inflammation doesn't actually occur until bacteria are in the wrong place -as long as they are outside of GALT, no inflammation -DCs take up antigen and release cytokines to communicate with T cells, so T cells mount a response -when they enter, T regulating cells (T-regs) release IL-10 to stop prevent/stop inflammation -there is also release of IL-17, TNFalpha, and IFNgamma by effector cells (these actually promote inflammation) -Neutrophils come in and phagocytose -*NETosis* they plug in holes/make a net where the cells are coming in, and explode -kills all the bacteria, but also harms the body -*Neutrophil Extracellular Traps (NETs)*: activated by PRR and expel filaments of chromatin and other cellular debris that entrap and kill pathogens -Neutrophil dies in process -cytoplasmic contents are spilled to form NETs -DNA/chromatin can act as DAMPs and activate local innate and inflammatory responses (other granulocytes do this too) -M cells are the patched of lymphoid tissue among the endothelial cells -Villi absorb nutrients, not supposed to absorb pathogens

Antibody Basic Diagram

Heavy Chain/ Fragment Constant Region/ Fragment Crystallized Region -part that has *biological* region Light Chain and Heavy Chain have variable regions -parts that contribute to *specificity* Hyper Variable Regions in Light and Heavy Chains -aka "Complementary D__ Regions 1, 2, and 3 -if something is complementary, those places are where antigen interacts with antibody in highest way -areas dictate how well antigen binds to antibody 4 proteins - 2 heavy and 2 light -bound together by disulfide bonds -broken apart if you target disulfide bonds

Hematopoiesis Overview

Hematopoiesis -formation of RBCs and WBCs/leukocytes Hematopoietic Stem Cells (HSCs) -difficult to study due to rarity -but can still be cultured, even though it's difficult HSC = Lymphoid and Myeloid progenitor HSC are homeostatically maintained -but they can rapidly divide HSC need to activate and have response, but not so much that causes tissue destruction or dysregulation -right amount of cells important in homeostatic function

Thymus: Basic Histology

Hematoxylin eosin stain Darker Blue = more cells -cortex where immature cells are Light Blue = sparse -medulla where mature cells are

Attack Mechanism of CTLs

In order to focus an attack more, there is cytoplasmic rearrangement -all vesicles with cytokines or granzymes are directed to the cell that needs to die CTL does NOT die after killing -CTL stays alive

Immune Organs: Phylogeny

Lamprey -no GALT -no Thymus (no T cells) Trout/FIsh -has GALT -has Thymus (fish can make T cells) Frog -has GALT -has Thymus -has Spleen -has Bone Marrow (has organ to analyze only blood derived antigens) (has hematopoiesis from bone marrow) Bird -has GALT -has Thymus -has Spleen -has Bursa (where B cells made) -has Bone Marrow -has Lymph Nodes (bone marrow is not the only place where B cells are made) Mouse -representative of the things humans have in the immune system -GALT, Thymus Lymph Nodes, Peyer's Patch, Spleen, Bone Marrow

Spleen

Large oval structure in left abdominal cavity Plays major role in mounting immune responses to blood-borne antigens -spleen NOT connected to lymphatic system -spleen ONLY for things associated with the blood -blood-borne antigens an lymphocytes arrive through splenic artery -lymphocytes concentrate along the artery -primary and secondary follicles along artery -only secondary follicles have GC Spleen is surrounded by capsule with projections/trabeculae extending into interior *Red Pulp* = mostly RBCs and Macs -Macs do remodeling, phagocytosis, cleaning up of RBCs *White Pulp* =where lymphocytes are -Periarteriolar Lymphoid Sheath (PALS): dominated by T cells -primary lymphoid follicles surrounded by PALS, which have B cells inside -Marginal Zone: separates the red and white pulp *If a person does not have a spleen, they are more prone to sepsis/infections of the blood*

Secondary Lymphoid Organs

Locations where mature lymphocytes interact with antigen -B and T cells that already HAVE antigenic specificity ENCOUNTER antigen they are specific to Includes Spleen, lymph nodes, MALT, and GALT -all of these include "lymphoid follicles" = collections of lymphoid and nonlymphoid cells surrounded by draining lymphatic capillaries Most organized = Lymph Node and Spleen -contain distinct B and T cell regions and fibrous capsules, in addition to lymphoid follicles

Quiz 4: Ikaros is the transcription factor for the ___ lineage.

Lymphoid

Quiz 5: Which of the following cell types separates the internal and external environments of the GALT?

M cells -make sure bacteria that are supposed to be there are, and bad are out -patches of lymphoid tissue among endothelial cells (part of Peyer's Patch, NOT the entire patch) -DO NOT have villi, so they can sample everything

Lymphatic System

Macs, Lymphocytes, DCs, and other immune cells gain entry to lymph/tissues Since lymphatic system drains all tissues, when foreign antigen enter tissue, it is eventually picked up by the lymph -lymph concentrates DCs, B cells, and antigen -problem is brought to T cell, rather than T cell looking for it -this way, T cell is activated by antigen and goes to site to work quickly Lymph carried to organized lymphatic tissues, such as lymph nodes *Summary* -lymph serves as means of carrying lymphocytes and antigens from connective tissues to lymphoid tissues -where lymphocytes can recognize antigen and become activated -lymph nodes and lymphatic system all over the body -swelling with a cold -lymph swells with antigen and other cells to present to T cells -Draining lymph node = concentration of antigen and other things to allow response -*Afferent* travels towards/ into lymph nodes -*Efferent* travels out of lymph nodes -there are circles/follicles inside of lymph nodes -follicles full of B cells -B cells become activated by FDCs and TFHs that present antigen to them -antigen and cells come into the lymph node -everything is concentrated, activating B and T cell -Unidirectional -cells and materials can't exit through afferent, only through efferent -secondary follicles are rapidly dividing

Lymphocytes

Major cells of the immune system -T, B, and NK Cells -NK Cells is outdated term -used to be "Null Cell" saying it had no TCR -this is wrong because they do have a TCR, so RECENT term is Innate Lymphoid Cell -NKC is a TYPE of ILC Stem Cells differentiate into B and T Lymphocytes in bone marrow -blocked from exiting G0 cycle phase until they are activated by binding of specific antigens into lymphocyte surface receptors (get BCR/TCR) -after activation, replication continues as lymphocytes circulate and enter lymphoid tissue -activated cells form "memory cells" or "effector cells" which stop at G0 and do not replicate anymore

B cell Activation: T-dependent

Majority of B cells are T-cell dependent to become activated 3 signals: 1)antigen binding to BCR 2) CD40/CD40 interactions to bind stimulation for full activation 3) Cytokines by TH Cell to drive response

B Lymphocytes

Mature in bone marrow Circulate in blood Can settle in lymphoid organs After maturation and activation, some become "Plasma Cells" that secrete large volumes of antibodies *Activation* -antigen binds to BCR -also dependent on T cells

T Lymphocytes

Mature in thymus, after which T lymphocytes can: -remain in thymus -circulate in blood -reside in lymphoid tissue Like B cells, T cells require antigen binding to TCR for activation and replication UNLIKE B cells: -antigen must be presented to T cells by APC in context of MHC Activated T cells produce cytokines: -proteins that have effects on other cells -Types: CD4+, CD8+, Tregs Intraepithelial T cells work different from what Dr. Larkin talks about 90% of the time

HSCs Needed for Reconstitution

Min number of cells needed for immune system/stem cell reconstitution = 1 1 HSC possible to give full reconstitution 20 HSCs would immediate full reconstitution, but JUST 1 is enough

Quiz 4: Which of the following cell types is not capable of self-renewal?

Monocytes Capable of self-renewal: - Erythroid cfu -Megakaryocyte -Basophil cfu

Quiz 3: Of the cell types listed, which is/are not phagocytic?

NON-phagocytic: -Basophils -Mast Cells -NKT Cells -B Cell -T Cell -Natural Killer Cell PHAGOCYTIC: -Eosinophils -Neutrophils -Dendritic Cells -Macrophages

Quiz 5: Which of the following is not a location of B cell development?

NOT: -appendix in humans ARE: -Bursa of Fabricus in birds -Appendix in rabbits -Fetal spleen to ileal peyer's patch in sheep and cattle

Activated B cells from Antigen-Depends Phase

Naive B cell encounters antigen -many B cells are T cell dependent Activated B cell can become Plasma Cell or Memory B cell *Memory B cell* through *affinity maturation* -important in immune response and vaccinations for bigger, better, faster responses -need high affinity antibodies that will ALWAYS combat antigen -do NOT produce antibodies *Plasma Cell* rearranges cytoskeleton to only spit out antibodies -no longer divides, ONLY makes antibodies -B cell can undergo *class switching* (dictates what isotypes of antibodies can be made) -class switching implies B cell can change to multiple classes when dividing -SPECIFICTY to antigen does NOT CHANGE -isotype/job of antibody can switch, depending on environment and T cells

Location of Hematopoiesis: The Bone Marrow Niche

Niche = specialized microenvironment HSC niche is sequestered region that contains stromal cells Stromal Cells: -connective tissue cells in any organ (fibroblast cell, endothelial cells, etc.) -regulate cell survival, proliferation, differentiation, and trafficking (forms nursery that provides all proper guidance for forming cell types)

Yoda Mouse/ Nude mouse

No fur on it Defective of T and B cells -lack adaptive immune responses

Quiz 5: The ___ pulp contains mostly RBCs and macrophages while the ___ pulp contains lymphocytes.

Parts of the spleen: 1) Red 2) White

Apoptosis

Perforin and Fas/FasL kill through PCD -apoptosis is FORM of PCD -not the only type of PCD Caspases = family of cysteine proteases -areas of research still ongoing -exist as *zymogens* (enzyme that is inactive until catalytic event converts the procaspase into a caspase) -Zymogen needs to be ACTIVATED (could harm the body if always on) -how immune system works quickly Caspases: -Procaspase 8 to Caspase 8 Initiator -Procaspase 9 to Caspase 9 initiator (Apoptosome) -Procaspase 3 to Caspase 3 (effector-executioner) -tear up actin cytoskeleton and cause cell undergo apoptosis

Adaptable/Inducible Effector Function

Phagocytic cells help other cells become more phagocytic -MHC II presents to Help T cells/ CD4 Infected Cells present MHC I to CD8 Cells/ T Cytolytic cells B cells make antibodies

Cytolytic T Lymphocytes (CTLs)

Possess effector function -eliminates cells bearing MHC complexed with FOREIGN antigen CTLs form conjugate with target cell -attack membrane of the cell - dissociate -Target cell dies Utilizes Fas on target cell -and Fas Ligand on CTL for interaction While associated with target cell, CTLs inject *perforins* and *granzymes* (serine proteases) which are NOT present in Naive CD8s CTLs have to be ACTIVATED -body will not expends energy on perforins and granzymes that are not needed -kills only when ABSOLUETLY necessary (different from NK cells, which are always on)

Lymphoid Follicles

Present in Secondary Lymphoid Organs -within Lymph Nodes and Spleen, and also exist independently *Primary Follicle* -before activation -contains FDC and resting B cells -NO germinal center (GC) -once B cell has sufficient activation in paracortex, travels to the follicle -primary follicle does not have enough space for rapidly dividing cells (are small) *Secondary Follicle* -after activation -packed circular ring of B cells surrounding Germinal Center (GC) -GC in center of mantle -GC contains rapidly dividing B cells, non-dividing B cells, TFHs, FDCs, and Macs -GC has class switching (Plasma Cells), Affinity Maturation (Memory Cells), and activation of high affinity B cells -activated B cells and antigen concentrate in follicle -concentrating antigen increasing probability of B and T cell activation and mounting response -FDC binds antibody and binds antigen -FDC presents antigen to TFH to activate it -TFH activates naive B cell for specific antigen -B cells screened through FDC -testing to see if B cells have high enough affinity to antigen on FDC -many cells go through PCD if not high enough affinity

Humoral Response to Antigens

Primary Antibody Response -peaks 10-17 days -mostly IgM -antibody levels increase then decline Secondary Response (Memory) -more rapid -peaks 2-7 days -mainly IgG -results in higher levels of antibody -antibody persist longer than in primary response (like in vaccinations)

Bone Marrow

Site of Hematopoiesis and B cell maturation Bone marrow B cells generate IgG and IgA (antibody isotypes) in plasma -part of the antibody has specificity and part of the antibody does the job -IgG and IgA DO the job -IgG binds to Fc region, IgA does not *ON EXAM* -Maturation of B cells in bone marrow ONLY in humans and mice -B cells mature in different places in other animals *ON EXAM* B cell development occurs in: -Bursa of Fabricus in birds -Fetal Spleen; Ilieal Peyer's Patch in Sheep and Cattle -Appendix in rabbits

Antibodies (Ab)

Soluble glycoproteins that bind antigens with high specificity and affinity 5 major isotypes: -*IgG* - most abundant Ig in blood/ monomer -*IgM* - 1st antibody produced in response to an infection in blood/ pentamer -*IgA* - major Ig in external secretions (milk, saliva, etc.)/ dimer -*IgD/IgE* - present in low concentrations in blood -IgE effective in eliminating extracellular parasites and allergies

Why do we isolate HSCs?

Stem cells have capacity to self-renew and give rise to lineages of differentiated cells Provide immune system to those with genetic immune deficiency -Severe Combined Immunodeficiency Disorder (SCID) -lack of B and T cells Replacing defective Hematopoietic System with functional one -done for Sickle Cell Anemia Restoration of Hematopoietic System -Done for cancer patients after high dose of chemotherapy and radiation -cancer patients can now "bank" their own stem cells -reconstitute after irradiation Can get rid of defective cells and put in functioning ones -cell therapies

How do we isolate HSCs?

Stem cells used to come from donor long bones -very painful, requires anesthesia Enriched stem cells from peripheral blood may be enough

T cell Activation

T cells have membrane bound TCR TCR recognize a peptide when it is bound to a *MHC molecule* on an APC -in addition to peptide and MHC, naive T cells also require interaction with other molecules on surface of APCs known as "*co-stimulators*" Activation steps help prevent T cell activation by harmless molecules T cells help B cells -B cells don't have specific needs for activation, because it depends on T cells -why T cell activation is very regulated -makes sure other cells aren't accidentally activated

TCR Complex

TCR - provides specificity for response TCR Complex - different *components* depending on what the target is -alpha-beta (a-b): common TCR already discussed [specificity] -zeta-zeta (z-z) -gamma-epsilon (g-e) -epsilon-delta (e-d) -ITAM = Immunoreceptor Tyrosine-Based Activation Motif -undergoes conformational changes -Tyrosines have OH groups *MEMORIZE* -region that is *Phosphorylated* -ITAM then forms docking sites where thinks can stick to them -then those things become activate Molecules on APC is presented to TCR, which activates TCR and many other things T cells will clonally expand and target and kill antigen -sometimes, viruses may activate more T cells so specific T cells are diluted in mass and pathogen lives longer T cell specificity does NOT have ITAMs -*accessory molecules* have ITAMs -they are associated with TCR and CONVEYS the activation -a-b are what do specificity

Quiz 3: NK Cells will kill a virally infected cell due to a downregulation of MHC I. This killing happens because the NK Inhibitory Signal is not bound.

TRUE NK Cells always present Activating Receptor and Inhibiting Receptor If MHC I is present and binds to Inhibiting Receptor, no killing occurs If MHC I is not present and bound, and ONLY Activating Receptors is bound, killing will occur

Thymus Change Overtime

Thymus gets smaller with age Large when young -developing active immune system and microbiome is shaping Smaller with age -immune system depends on memory Reason why young and old are most susceptible to infections -young still shaping immune system -old can't change/develop T cells for changes

Thymocyte Apoptosis

Thymus is where T cells get functional maturity with addition of TCR Some cells never recognize antigen or recognize self too strongly -90% of thymocytes undergo PCD because they don't function correctly Cells are more defined under Scanning Electron Microscope (SEM)

Quiz 4: Most of what we know about the role of transcription factors in hematopoiesis comes from the use of knockout mice. True/False

True

Quiz 5: Edema occurs as a result of fluid not being returned to the blood. True/False

True

Quiz 5: More than 95% of thymocytes die by apoptosis. True/False

True

How Virus Titer Works

Virus titer increases and decreases *Decrease* in virus titer when there is an *increase* in virus specific CTLs *Increase* in virus titer when more cells become infected by virus Increase in NKCs -kill infected cells When virus titer is back down, everything goes back to homeostatic level

Quiz 5: Which of the following stages of T cell development is improperly matched with its region?

WRONG: -DP, subscapular cortex CORRECT: -SP, medulla -SP, cortex -DN, subscapular cortex -DP, cortex

Immune cells of the Adaptive Immune Response

Where they acquire antigenic specificity B cells -get BCR in bone marrow -more antigen specificity in GC of secondary follicles T cells -T Helper Cells and T Cytolytic Cells -get TCR and specificity in thymus

Primary Lymphoid Organs

aka "Generative Organs" -location where lymphocytes first express antigen receptors and get functional maturity *Bone Marrow* -site of generation of all circulating blood cells in adults -site of early B cell (immature lymphocyte) maturation -memory B cells in plasmacytes RETURN to bone marrow -stay in bone marrow in case infection happens again, and can come back quickly -preferential niche of plasma and memory B cells *Thymus* -location of T cell maturation -cortex contains thick collection of mostly immature thymocytes -medulla contains mostly mature T cells that are immunocompetent *Periphery* -lymph nodes and spleen

Thymus Location

located above the heart Thymus = opaque blob of junk -harder to find in older mice Where T cells develop