Ch. 15: Immune System

Antibodies (2)

reminder: produced by B cells differentiating into plasma cells which secrete antibodies primary immune response: (1st exposure) -after 1st contact with antigen-slow production of antibodies but that production includes memory cells -generally takes 10-17 days to occur after exposure -symptoms of illness occurs during these days secondary immune response: (all other exposures) -next contact with that antigen produces quick production and action of the antibodies -takes hours-7 days to occur -occurs due to memory cells -memory cells grow in number through childhood, the most abundant type of lymphocyte in adulthood and then decline after 70 yrs old

Lymphocyte Cells - T Cells

T cells: -mature in the thymus, clone -receptors again re unique to one antigen -cell mediated, need MHC & antigen to bind -there are 3 types: 1.) cytotoxic: -travel to targets and kill it by binding to the antigen and secreting chemicals -can occur to body's own cells-that are infected or cancerous -kills viral and fungal infections 2.) helper: -assist activating and the functions of B cells through direct contact, cytotoxic T cells through helping other cells to help cytotoxic cells -without helper cells, the two could not function adequately 3.) regulatory: -inhibits B and cytotoxic T cells -destroys own proteins, suppress inappropriate responses and prevent autoimmune diseases -people with autoimmune diseases may have problems with the regulatory T functioning properly

Immunity

active immunity: -resistance to infection due to contact with microorganisms and toxins or antigens vaccine: -the introduction of a microorganism or its antigen (inactivated pathogens, antigenically similar but less harmful, genetically engineered), which induces an immune response including production of memory cells passive immunity: -transfer of antibodies form one person to another such as: -a mother to fetus or baby because a antibodies pass in the placenta and breast milk -injections given to a patient suffering from certain infections -intravenous for autoimmune or cancer patients

Immune System Communication

cytokines: -protein messengers (regulatory) -produced by a variety of immune cells -for the most part: actions occur at secretion site and may occur to a broad range of target cells -allows different immune system cells to "talk" to one other vie chemical messages -"cross talk" vital to the timing of immune response -chemokines: subclass, are chemical attractants (attracting phagocytic cells)

Other immune Cells: Dendritic and Mast Cells

dendritic: -highly motile -located all over especially in places where external/internal environments meet ex: digestive -process phagocytize pathogens -main antigen-presenting cell to T cells mast cells: -release histamine -histamine helps stimulate innate immune response -this increases permeability of capillaries-more fluid enters extracellular space producing an edema (swelling at the inflammation site)

Steps in Response to a Wound

ex: splinter -chemical mediators (mast cells producing histamine) dilate vessels in infected/damaged area -at these locations the membranes of the capillaries/venules become permeable to proteins -this allows increased blood flow and increased proteins participating in the inflammation -the vasodilation and protein causes increased fluid-edema, which is the swelling -neutrophil (a type of myeloid cell) enters the inflamed area -first to arrive -this is an example of the leukocytes moving out of the circulatory system -chemotaxis (multistage process of cells moving and adhering in the injured area) -one neutrophil is attached to the endothelial cells, chemoattractants (messengers) act on the neutrophil and another adhesion molecule attaches to endothelial cell-neutrophils begin collecting -next, diapedesis (where neutrophil squeezes itself into the interstitial fluid), there is migrates to the site of damage -once present at the damage site, the cells destroy the invaders by phagocytosis -the microbe (invader) engulfed is enclosed in a sac and known as phagosome in the cell -the lysosome of the cell will connect with the phagosomes to break down the microbe -to repair the tissue in the final stage of this process, cell division may occur depending on location -skeletal muscle cells do not divide -if there is a scar, the repair work was imperfect

Toll Like Receptors

function: -recognize and bind to pathogens -specifically they look for a general feature: lipid/protein/carbohydrate they can bind to -once bound, immune cells (dendritic and macrophages) are stimulated in a innate immune response -the role these receptors play was recognized in 2011

Nonspecific Defenses: Physical Signs of an Invader

inflammation: -local response to infection or injury -function: destroy or inactivate foreign substances and set the stage for repair by attracting additional immune cells and stimulate their activity -signs accompanying inflammation are often local redness and pain fever: -body temp is re-set upward in response first to cytokine from leukocytes but then the brain produces continual response -benefits include increased activity of neutrophil and interferons (proteins acting on viruses)

Defense

two categories: 1.) innate: -inherited general defense 2.) adaptive: -cells change throughout lifetime to combat pathogen -we often use both categories to fight off a pathogen (harmful agent)

Major Histocompatibility Complex (MHC) Molecules

two classes: -class I MHC: -expressed on the surfaces of all nucleated cells -class II MHC: -expressed on the surface of macrophages, activated B cells, and dendritic cells (antigen presenting cells)

Lymphocyte Cells - B Cell

-B cells mature in bone marrow, cloned, differentiate into plasma cells to secrete antibodies -B cells remain at the location of activation and send plasma cells to travel through your body looking for antigens that are identical to whatever triggered their activation -B cells trigger a antibody-mediated response: targets bacteria, viruses, toxins -ONLY ONE ANTIBODY per plasma cell meaning one receptor unique to binding with an antigen is present -the human body therefore has to have lots of B cells to code for lots of different antigens *plasma cells release antibodies to find antigen, B cells lazy*

Immunoglobulins - Antibody Proteins

-B lymphocytes have antibodies ont heir membranes for antigens -5 major classes: IgA, IgD, IgE, IgG, IgM -the polypeptide chain has an antigen-binding site varying in amino acid sequence at on end to give us millions of unique immunoglobulins each capable of combining with a specific antigen -therefore B cells have immunoglobulin receptors determined during maturation of the cell (each being unique as DNA is rearranged in these cells) that are designed to bind to an antigen if that antigen invades the body

Recognize Yourself

-T cells are also unique like B cells due to DNA rearrangement -however, T cells need the body's own membrane proteins to bind it with an antigen -proteins are called major histocompatibility complex (MHC) -proteins that are unique to you and only you (unless you have an identical twin) -are expressed on your cell surfaces

Class I MHC Protein don Cytotoxic T Cells

-antigens are within cells since this T cell is focused on destruction of body's own cells that are infected with viruses or cancerous -viruses cause host cell to manufacture viral proteins -cancerous cell has genes altered that are coding for proteins not normally found in the body -T cells kill the cell *not always the case, depends on the antigen and MHC*

Macrophages

-derived from myeloid precursor cells -found in almost all organs and tissues -placed at the skin, surfaces of respiratory and digestive tubes so they will encounter pathogens/particles trying to enter the body -clean away dead cells

Phagocytosis

-func fact: cells i the liver and spleen the are capable of conducting phagocytosis are fixed -as blood flows through these, cells remove foreign chemicals and debris

Tying it all Together

-innate defenses respond to foreign substances, like bacteria, without having to recognize their identities -adaptive defenses depend on recognition, lymphocytes are the key player in this type

Antibodies

-link the microbe to phagocytes -the do not do the killing themselves, they recognize!

Adaptive Immune Defenses

-lymphocytes recognize specific foreign molecules called antigens -antigens stimulate production of specific antibodies -antigens are usually proteins or polysaccharides, any molecule that host does not recognize as "self"

Example Summary of Events for Bacterial Infection

-macrophage breaks down bacteria -T cell recognizes antigen after is has bound to MHC protein -helper T cell binds to it -helper T cell sends out messages -B cell in this case responds -B lymphocyte on it travels through the lymphatic system encounters an antigen -memory cells store -plasma cells make antibodies -antibodies bind to antigens -T cells then will bind and destroy

Myeloid Cells

-neutrophils -monocytes - macrophages major importance: -secrete inflammatory mediators

Nonspecific Defenses: Defenses at Body Surfaces

-the body's first line of defense against microbes are the barriers offered by surfaces exposed to the external environment and their various glands that secrete antimicrobials -examples: skin and mucous membranes (along GI and respiratory tract) -cough and sneeze reflex and the hairs in your nostrils provide a defense too

Leukocytes

-the cells of the immune system (aka white blood cells) -are able to leave circulatory system two groups: -myeloid-innate -lymphoid-adaptive, lymphocytes recognize cells in adaptive immune responses -myeloid and other types of cells secrete inflammatory mediators and function as phagocytes among other activities

Lymphoid Organs

-the majority of lymphocytes are not circulating in the blood, but rather in the lymphoid organs, where they are produced and activated (wait for pathogen) thymus: -located in the chest -holds cell shot will develop into mature T cells lymph nodes: -nodes scattered along the vessels spleen: -left area of abdominal cavity -blood passing through here encounters lymphocytes, macrophages, dendritic cells tonsils: -in the pharynx -respond to microbes arrive through ingestion or inspiration lymph: -fluid in the lymphatic capillaries -where lymphocytes in the lymph nodes encounter antigens -movement: lymphocytes→primary lymphoid organs→blood→lymph nodes→lymph

Innate Immune Response: a nonspecific defense

-these defenses recognize some general property marking the invader as foreign and they protect the body as the first line of defense -have toll-like receptors. pathogen recognizing receptors the nonspecific defenses include: -physical barriers -fever -phagocytosis (type of endocytosis) -interferons -does not require memory, or past exposure, it's inherited -use myeloid cells (neutrophil) for this response

Nonspecific Defenses: Interferons

-type of cytokine: small proteins two types: -type 1: nonspecifically inhibit viral replication in host cells -ex: upon viral replication, binds to membrane of secreting and other cells-binding triggers different antiviral proteins that interfere with replication process of the virus -type 2: produced by immune cells -enhances activity of macrophages, acts as chemoattractant in chemotaxis

Class II MHC Proteins on Helper T Cells

1.) antigen is phagocytized by antigen-presenting cell in a nonspecific response and broken down 2.) antigen fragments bind to MHC II -MHC II has recognized the fragment as "non-self) 3.) vesicle presents MHC antigen complex on the surface of antigen presenting cell 4.) T cell now recognizes it as foreign-when the antigen is complexed with MHC, interactions between other proteins occur at the membrane, and cytokines are released

3 Stages of Adaptive Immune Response

1.) encounter and recognition: -each lymphocyte presents a receptor for a certain antigen-in other words is specific to one antigen type -determined during development -once the specific antigen is recognized it is bound 2.) lymphocyte activation: -once bound, undergoes rapid mitotic division -some are used in attacking invaders, the rest are stored (memory cells) 3.) attack is launched: -B cells differentiate to plasma cells and dump antibodies into circulation -cytotoxic T cells directly attack pathogen -when attack is over, and the pathogen defeated, most of the effector cells undergo apoptosis, but some remain for memory -apoptosis prevents the response from getting excessive and destroying healthy tissues

Lymphoid

primary lymphoid organs: (PRODUCE) -lymphocyte development-not activated by specific antigen yet 1.) bone marrow - produces B cells 2.) thymus - produces T cells secondary lymphoid organs: (ACTIVATE) -mainly spleen, lymph nodes, tonsils -all lymphocytes are descending from cells that matured in the primary organs