Chapter 11.3

A decrease in antibody production would be caused by a

B cell deficiency

Immune response 2 categories

Innate and adaptive

A platelet deficiency would decrease the conversion of

prothrombin to thrombin

Lymphocytes

-These are a type of leukocytes which originate from the bone marrow but end up concentrating in lymphatic organs (e.g. lymph nodes, spleen, thymus) -The B cells and T cells that we will talk about later are lymphocytes! :)

These physical/physiological barriers serve as the first line of defense. However, if they are penetrated, the rest of the innate immune response kicks in.

1. Alarm, enemy detected — activation of the inflammatory response 2. Rally — recruitment of troops (aka. immune cells) to the site of injury 3. Battle — immune cells attack pathogens 4. Backup — activation of the complement system In cases when the innate immune response is inadequate, the adaptive immune response will step in to kill off the enemies.

Active Immunity

Active immunity is DEVELOPED by the organism when a pathogen invades the body and prompts an innate or adaptive immune response. When we administer pathogens in vaccination, it provokes active immunity. The vaccination introduces a small amount of weakened or dead pathogen to our body (in a form that is not pathogenic, or disease causing), which stimulates an immune response. This type of active immunity is ARTIFICIALLY ACQUIRED. Vaccines will induce the formation of memory B cells and T cells that remain in our body to protect us against future exposures of the real pathogen.

Innate immunity - immune cells and molecules

After the capillaries become permeable under the influence of histamine, immune cells rush to the site of injury and begin the battle against pathogens. The process of cells moving from capillaries to tissues is called DIAPEDESIS. The process of moving to a location in response to a chemical signal is called CHEMOTAXIS. 'Chemo' = chemicals, and 'taxis' = movement. In the inflammatory response, many white blood cells are drawn to the site of injury via chemical signals.

Decrease in heparin release would be caused by

Basophils - Heparin is a type of anticoagulant that functions to decrease the clotting ability of the blood. It is one of two important contents within granules that is contained by basophils.

Clonal selection model

This theory states that since each B cell has a unique BCR, the antigen selects which BCR it can bind to and which B cell to activate. Therefore, out of thousands of pre-existing B cells, only one specific B cell is selected to proliferate and make clones of itself. We have amplification of the B cell that is specific to the antigen that is present in the pathogen of attack.

Proliferation of cancerous cells would be caused by a deficiency in

Granzymes

antibody

Antibodies are typically Y-shaped, consisting of a LIGHT chain and a HEAVY chain linked through DISULFIDE BONDS. The constant regions have very similar amino acid coding sequence (antibody is a protein after all!) within a particular class of antibodies. The hypervariable regions are the ones that bind to different antigens; that's why they have different amino acid sequences. Differences in the hypervariable region of antibodies allow for specificity; this region of the antibody is able to bond to specific antigens. This specificity is what makes the adaptive (specific) immune system effective at marking antigens for destruction. The tail region (the trunk of the Y) of the antibody is the Fc region (fragment crystallizable region). The top of the Y is the fragment antigen binding (Fab). The variable region is the subregion of the the Fab that binds to the antigen. Antibodies are GLYCOPROTEINS, where a carbohydrate is added to amino acid residues. The glycosylation sites occur in the Fc region, and influence interactions with effector molecules.

Dendritic cells

"surveillance guards roaming in tissues detecting potential threats" A dendritic cell can scan its local environments by taking a sip from its surroundings through a process called pinocytosis. Once it detects a pathogen, it will phagocytose the pathogen like macrophages and neutrophils. PINOCYTOSIS = cell drinking PHAGOCYTOSIS = cell eating Similar to macrophages, dendritic cells also play the role of antigen-presenting cells. Dendritic cells then migrate to lymph nodes along with macrophages to activate the adaptive immune response. Both macrophages and dendritic cells utilize toll-like receptors (TLR's) to recognize parts of conserved molecules that belong to microbes. When these receptors bind, they are able to trigger phagocytosis and activate other elements of the innate immune system. Another important molecule that links the innate and adaptive immune systems is INTERFERON. Interferon is secreted by virus-infected cells to warn nearby non-infected cells. Interferon will act as a messenger and bind to non-infected cells to help them be prepared for a viral attack. Interferons also help activate dendritic cells, which helps kickstart the adaptive immune response.

critical review 4

- Adaptive immune response: specific, targeted protection - Antigens: any molecule recognized as 'non-self' that can trigger an immune attack - MHC I: found on all nucleated body cells -- Mark for 'self' -- Foreign MHC I molecules are deemed as antigens (i.e. organ donation) - MHC II: found only on APCs - APCs (macrophages + dendritic cells) present antigens on MHC to B cells and T cells - Epitope: important part of the antigen that is recognized by immune cells - Lymphocytes: -- B cells → born in bone marrow → mature in bone marrow -- T cells → born in bone marrow → mature in thymus -- Natural killer cells → born in bone marrow → stay in bloodstream

critical review 5:

- B cells → antibody-mediated immunity/humoral immunity - BCR = antibodies = immunoglobulins --BCR is the bounded version -- BCR can bind to free or presented antigens -- Unique and uniform -- Antibodies/immunoglobulins are freely secreted - B cells can become: -- Plasma cells: release antibody -- Memory B cells: don't release antibody, retain memory of antigen for future preventions. Key to vaccinations - Antibody: -- Y-shaped, heavy + light chain, constant + variable region -- 5 classes: IgM, IgA, IgE, IgD, IgG

critical review 3:

- Complement system: a team of ~30 blood plasma proteins (not cells) - The complement system is part of innate immunity - Membrane attack complex (MAC) → poke holes in pathogen membranes → cell lysis

Adaptive Immunity- T cells

- In the adaptive immune response, T cells are responsible for cell-mediated immunity. Contrary to B cells, which send out antibodies to do the job of killing enemies (humoral response), T cells do the work themselves (cell-mediated response). - Similar to B cells, T cells have T cell receptors (TCR) on their surfaces. Every T cell has a unique and uniform TCR that binds to only one kind of antigen. Hence, T cells also go through clonal selection. However, unlike B cells, T cells are more needy. T cells cannot recognize free floating antigens; they can ONLY bind to antigens presented by antigen presenting cells (APCs). - The most common APCs that serve T cells are macrophages, dendritic cells, and B cells. Recall we mentioned that antigens can be presented on either MHC I or MHC II molecules.

Critical review:

- Innate immune response: nonspecific, generalized protection - First line of defense: barriers to block pathogen entry -- Skin, mucosa, oil gland, acid, antimicrobial enzymes (lysozymes), cilia, symbiotic bacteria

critical review 2:

- Mast cells release histamine 1. Dilate capillaries 2. Make capillaries more permeable - There are 5 signs of inflammation: redness, heat, swelling, pain, loss of function

plasma cells

- Plasma cell release antibodies, also known as immunoglobulins -- Structurally, BCR and antibodies are identical. BCR is bound to B cell membrane, whereas they are called antibodies when they are freely secreted. - Antibodies are also known as immunoglobulins. Antibodies circulate in the blood and lymph

If an antigen is presented by MHC I:

- T cells activate and become cytotoxic T cells, also called CD8 cells -- They are called CD8 cells because they form a co-receptor CD8 in addition to its original TCR - CD8 cells will recognize every cell containing the presented antigen, and kill it To see how CD8 cells kill pathogens, we need to go back a bit to innate immunity and compare CD8 cells and their close relative, natural killer cells. Similarities: - Both release: -- Perforin: perforates (poke holes in) pathogenic cell membranes, causing cell lysis (cell breakdown) -- Granzymes: a protease which stimulates a target cell to undergo apoptosis (programmed cell death)—useful for killing cancerous cells Differences: - NK cells react faster than CD8 cells because they do not require antigen-presentation and activation - CD 8 cells are more specific than NK cells because they target a specific antigen on a pathogen

If an antigen is presented by MHC II:

- T cells activate and become helper T cells, also called CD4 cells -- They are called CD4 cells because they form a co-receptor CD4 in addition to its original TCR - Helper T cells are there to assist both innate and adaptive immunity -- They release cytokines to ramp up the immune response - Functions of cytokines: -- Attract innate immunity cells e.g. macrophages, dendritic cells to where the identified antigen is present -- Stimulate clonal selection and proliferation of B cells and T cells

Critical review 6:

- T cells → cell-mediated immunity - TCR: -- Can only detect antigens presented by APCs, NOT free floating antigens -- Unique and uniform - Cytotoxic T cells kill enemies in the same fashion as natural killer cells

After antibodies are released into the humor, they can:

- Tag the specific corresponding antigen for removal → signal it should be phagocytosed - Coat the antigen in antibodies, which neutralizes it - Activate the complement system These functions all share a common goal — annihilate the pathogen containing the specific antigen.

Pathogens:

- These are all kind of harmful microscopic enemies (virus, bacteria etc...) that can cause diseases. -Many pathogens are bacterial in nature; common examples of diseases that are caused by bacteria include tuberculosis, gonorrhea, and syphilis. Tuberculosis is a disease that often affects your lungs and can lead to death if left untreated; it is caused by the acid-fast bacterium Mycobacterium tuberculosis. Gonorrhea is a sexually transmitted disease (STD) that is caused by Neisseria gonorrhoeae. Syphilis is another STD; it is caused by Treponema pallidum.

Memory B cells

- These cells live for a long time in our bodies, sometimes even for decades - They do not release antibodies - They save the information about the antigen, and if the same antigen intrudes again within their lifespan, they will rapidly differentiate and proliferate into plasma cells to secrete the corresponding antibodies - Memory B cells are key to vaccinations. The goal of a vaccination is to introduce a small amount of weakened or dead pathogen to our body. Right after the injection, our B cells would produce memory B cells in response to that specific antigen. Later on in our life, if we happen to come across that same pathogen again, our immune system can rapidly produce antibodies to counterattack before the pathogen proliferates. - In addition to these two cell types, B cells can also act as antigen-presenting cells like macrophages and dendritic cells.

5 signs associated with inflammation

1. Heat - Heat is a result of dilation of capillaries; when there is increased blood flow, the tissue gets warmer 2. Redness - Redness is also a result of dilation of capillaries; more blood = redder color 3. Swelling - Swelling is a result of permeable capillaries; when blood vessels become leaky, fluid starts accumulating in nearby tissues, causing swelling 4. Pain - There are two types of pain when you get hurt: a sharp pain that happens right at the time of injury caused by nerve endings, and a slower, throbbing pain that you feel afterwards, which is caused by inflammation - For the pain from inflammation, it is because the swollen areas exert pressure on free nerve endings, which causes a continuous pain. (That's why it hurts even more when you press a swollen ankle!) 5. Loss of function - This is more of an indirect outcome of inflammation. When there is swelling and pain, that part of the body becomes less useable. For example, when people suffer from arthritis (inflammation of joints), they can't really walk normally. This has a beneficial effect of causing disuse of the injured area, aiding in healing. *DAT Mnemonic: inflammatory response → SLIPR: Swelling Loss of function Increased heat Pain Redness Sometimes, fever can result from an inflammatory response. Fever is turned on and off by the brain. It is not a local response anymore — it becomes systemic (body-wide). When our body's temperature increases, it helps to hinder the growth of pathogens, and may sometimes kill the temperature-sensitive ones as well.

When activated, the complement system can do a lot of things, including:

1. Improving the 'eating' ability of phagocytosing cells (eg. macrophages) by binding complement protein C3b to antigens and tagging them for phagocytosis, a process called OPSONIZATION 2. Amplifying inflammatory responses - Certain proteins can bind to mast cells to trigger a stronger histamine release 3. Lysing pathogen membranes - Some proteins can form a membrane attack complex (MAC) which specifically functions to poke holes in pathogen membranes -- Once holes are created, fluid and salts can go into the pathogen and make the cell burst and die Summary: 1. Membrane attack complex proteins group on the membrane of a pathogen 2. This allows salts and fluids to enter the pathogen 3. This causes swelling within the pathogen, causing the pathogen to burst

Memory T cells

A third type of T cells that form after clonal selection is memory T cells. Just like memory B cells, these long-lived cells are crucial to protecting our body from future invasion of the same antigen. If there is another encounter with the same antigen, the memory T cells will help the adaptive immune response to 'turn on' more quickly.

Which of the following components of the immune system responds to specific antigens?

B cells - There are two parts to the immune system: specific and nonspecific defense. Specific defense responds to antigens, such as the toxin from an insect sting, or a molecule on the plasma membrane of a pathogen. Nonspecific defense is not specialized for a particular pathogen; it defends against all pathogens in general. Examples of nonspecific defenses include: skin, interferons, phagocytes, cilia, and lysozyme. Interferons are molecules secreted by cells invaded by viruses that stimulate other cells to help defend against viruses. Phagocytes are white blood cells that engulf pathogens. Cilia line the lungs and help sweep pathogens out of the lungs. Lysozyme is a protein that breaks down cell walls in bacteria.

summarizing the three type of differentiated T cells:

CELL TYPE: - Cytotoxic T cell (CD8 cells) TCR ANTIGEN: - Presented by MHC I FUNCTION: - The CYTOTOXIC T CELL becomes activated when a foreign antigen is presented on MHC I. Chemical signals form HELPER T cells increase this activation - Once activated, cytotoxic T cells KILL pathogens containing the detected antigen. They release PERFORIN and GRANZYME CELL TYPE: - Helper T cell (CD4 cells) TCR ANTIGEN: - Presented by MHC II FUNCTION: - The HELPER T CELL becomes activated when. foreign antigen is presented on MHC II - Once activated, a helper T cell released CYTOKINES to recruit innate immune cells and help out with clonal selection of B and T cells CELL TYPE: - Memory T cell TCR ANTIGEN: - Formed after both MHC I and II FUNCTION: - LONG-LIVED T cells that are able to quickly proliferate upon RE-EXPOSURE to an antigen to which they have memory of

5 main types of leukocytes (WBCs) and functions

Here is an acronym for remembering the relative number of leukocytes circulating in the blood from highest number of cells to lowest number of cells in circulation: Never Let Monkeys Eat Bananas Neutrophils -> Lymphocytes ->Monocytes/Macrophages -> Eosinophils -> Basophils Never = Neutrophils - Neutrophils are your infantry units, the most numerous and common type of leukocytes. About 40-70% of leukocytes are neutrophils! Neutrophils are phagocytes — they eat (phagocytosis) and destroy pathogens. They are part of the innate response because they are not picky eaters — they engulf all kinds of pathogens. Let = Lymphocytes - Lymphocytes are your artillery units, the ones who identify and acquire a target before killing it. The lymphocytes are B cells, T cells, natural killer cells. - The B cells and T cells are part of the adaptive immune response, whereas the natural killer cells are part of the innate immune response. - Natural killer (NK) cells attack and kill virus-infected cells or cancerous body cells. They are part of the innate response because they do not require activation; unlike B cells and T cells, they are always "on". - NK cells fight enemies with two main weapons: -- PERFORIN, which perforates (poke holes in) pathogenic cell membranes, causing cell lysis (cell breakdown) -- GRANZYMES, a protease which stimulates a target cell to undergo apoptosis (programmed cell death)—useful for killing cancerous cells Monkeys = Monocytes/Macrophages - Monocytes are also part of the innate response. They are called monocytes when they are in their immature state in the blood vessels. After they cross into the infected tissue through diapedesis, monocytes mature into macrophages - They are similar to neutrophils in that they are also phagocytes. They also 'eat things' that should not be in the body in a nonspecific way. Later on, macrophages function as antigen-presenting cells to activate adaptive immunity. You can think of an antigen as the unique ID of the enemy. Macrophages act as messengers that carry vital information about the enemies from the frontline soldiers (innate immunity) to the backup troops (adaptive immunity). Eat = Eosinophils - Eosinophils are also part of the innate response. Their cytoplasms are filled with granules which contain proteins that can be released into the surrounding tissue to kill pathogens. They are especially effective against parasites. Bananas = Basophils - Finally, basophils are the least numerous kind of leukocytes. They only make up less than 1% of all leukocytes. Similar to eosinophils, basophils also contain granules that can be released to nearby tissues. Two important contents of the granules are histamine and heparin. We are familiar with the functions of histamine — vasodilation and making capillaries more permeable. Heparin, on the other hand, is a type of anticoagulant which prevents blood from clotting too quickly. - Basophils are similar in function to mast cells, but they come from different cell lineages. The difference is that basophils leave bone marrow (site of blood cell production) as mature cells and remain circulating in the blood, whereas mast cells leave the bone marrow and circulate the blood as immature cells, only maturing when they enter the tissue.

Asthma is characterized by an excessive inflammatory response in certain areas of the body such as the bronchial tubes. Which of the following is the most viable mode of action for a medication that is meant to alleviate this condition?

Histamine suppressant - Histamine is a substance involved in the inflammatory response that has two primary functions: (1) dilate nearby capillaries, and (2) increase the permeability of capillary walls. Specific leukocytes called mast cells and basophils release histamine, commonly in response to an injury or allergen. Histamine stimulates bronchoconstriction by mediating smooth muscle contraction, making it difficult for asthma sufferers to breathe. - Whenever there is an allergen, immunoglobulin E (IgE) will bind and trigger the release of histamine from mast cells and basophils. In patients with asthma, this triggers the airway inflammatory response, resulting in airflow obstruction, bronchospasms, etc. - Thus, we can reason that histamine plays a critical role in the pathogenesis of asthma. The most viable mode of action for an asthma medication is histamine suppression.

adaptive immunity response

If innate immunity isn't sufficient to protect us from pathogens, the adaptive immunity joins the battle. The adaptive immunity is a specific immune response because it targets specific antigens. An antigen is a marker from a foreign molecule that is able to trigger an immune response. Antigens serve as targets, and our body will mark the cells bearing the antigen as non-self. Our immune system is normally programmed to recognize its own cells and not attack them. How does it distinguish between self and non-self cells? It accomplishes this through the MAJOR HISTOCOMPATIBILITY COMPLEX (MHC) molecule found on the surface of cells. All nucleated (cells with a nucleus) body cells bear MHC class I molecules on their cell surface. Every genetically-unique individual will have his/her own unique set of uniform MHC I molecules. This means that identical twins (which are genetically identical) will have the same MHC I expression on their cells. When our immune system sees its own MHC I molecules, it will recognize these cells as allies and spare them from death. The MHC molecule is made up of alpha 1, 2, 3 and beta-microglobulin protein chains

Innate immunity - Inflammatory responses

If the protective wall is penetrated, innate immunity continues with the inflammatory response. This is why when you accidentally cut yourself, the injury site reddens and swells up after a few minutes. The first part of the inflammatory response is rally signalling. The mast cells are responsible for this. Mast cells are a type of leukocyte that sits in tissues. As soon as there is an injury, the injured tissue and mast cells work together to release a substance called histamine. Histamine has two main functions: 1. Dilate nearby capillaries → increase blood flow 2. Make capillary walls more permeable → fluid and immune cells leak out to the site of injury. Inflammatory response summary: 1. Mast cells detect injury nearby cells and release histamine 2. Histamine release increases blood flow in capillaries and makes the blood vessels more permeable

Critical review 7:

Immune System (Adaptive or Innate) ADAPTIVE (T cell or B cell) T cell (cell mediated immunity) - Memory T cells (faster immune response in subsequent exposure to antigen) - Cytotoxic T cells (CD8) (release perforin and granzymes to destroy tumor and virus-infected cells) - Helper T cells (CD4) (activate B cells, cytotoxic T cells, and additional helper T cells) B cell (antibody-mediated immunity) - Memory B cells (faster immune response in subsequent exposure to antigen) - Plasma cells (produce antibody that tags specific antigen for removal; activate complement system; coat pathogen and neutralize it) - Antigen presenting cell (present antigens on MHC Class II to activate immune cells) INNATE (Bloodborne or Physical) Bloodborne (Leukocytes or Complement Cascade or Inflammatory Response or Other) Leukocytes - Neutrophils (most abundant WBP; phagocytose pathogens) - Natural Killer cells (attach virally-infected and cancerous cells; use perforin and granzymes to lyse cells) - Monocytes/Macrophages (phagocytose pathogens; act as APC (MHC Class II) for adaptive immunity - Eosinophils (release granules against pathogens) - Basophils (release granules with histamine (vasodilation) and heparin (inhibit blood-clotting) Complement Cascade Inflammatory Response - Mast cells (release histamine (vasodilation) Other - Dendritic cells (pinocytosis/phagocytosis; act as APC (MHC Class II) for adaptive immunity) - Interferons (secreted by virally-infected cells and bind to non-infected cells to prepare for virus attack) Physical - skin - mucose membrane - saliva - urine - stomach acid - antimicrobial enzymes (lysozymes) **LOOK AT LAST PAGE OF THIS CHAPTER SECTION FOR REALLY HANDY IMMUNE SYSTEM DIAGRAM BREAKDOWN** - Passive immunity: antibodies are given to an organism, not acquired -- IgG — transfer through placenta -- IgA — transfer through breastfeeding - Active immunity: acquired immunity - Vaccines: artificially stimulates active immunity

Which of the following would be expected in an experimental protocol where a person is injected with a novel pathogen that secretes proteins to block toll-like receptors?

Impaired activation of innate immune responses - Toll-like receptors (TLRs) are membrane-spanning receptors expressed on cells such as macrophages and dendritic cells that recognize parts of conserved molecules that belong to foreign microbes. When microbes infiltrate the body, TLRs are able to recognize these intruders and initiate an innate immune response. If they are blocked, the activation of the innate immune system that is able to combat these microbes will be impaired.

Adaptive immunity - B cells

In adaptive immunity, B cells are responsible for ANTIBODY-MEDIATED IMMUNITY, which means that they control the production and release of antibodies. It is also called HUMORAL IMMUNITY because humor = body fluid, and antibodies are found in various types of body fluids, such as blood and lymph. B cells have B cell receptors (BCR) to bind to the epitope of the antigen. BCR can bind to free-floating antigens or antigens that are presented by APCs. After BCR binds to its antigen, the B cell becomes activated. Following activation, the B cell divides and makes many copies of itself. Every B cell has a unique and uniform BCR that binds to one kind of antigen, which means that a single B cell cannot have different BCRs that bind to different antigens.

In cases of organ transplantation:

In cases of organ transplantation, the donor organ will bear a different MHC I molecule, which will be labelled as an antigen by our immune system. As a result, our immune system will attack the "enemy" organ. This will lead to organ failure and transplant rejection. This is why transplant patients need to take immunosuppressants on a life-long basis to lower/eliminate the immune system's response towards the foreign organ. However, suppressing the immune system also makes these patients more susceptible to general infections.

Innate immunity provides protection via which of the following mechanisms?

Inflammatory response - An important part of innate immunity is the inflammatory response, which is generated in quick response to an injury or penetration of your body's innate barriers. - Opsonization via immunoglobulin-G is a specific way of tagging pathogens via antibodies for subsequent phagocytosis, and antibodies are an important part of adaptive immunity. So, "Opsonization via immunoglobulin-G" and "Tagging of pathogens via antibodies" are incorrect. - Adaptive immunity creates memory B and T cells to counter another infection of the same pathogen, so "Memory of previous pathogenic infections" and "Clonal proliferation of B cells" are incorrect. * The inflammatory response is a part of innate immunity, and generates a quick response to injury. Antibodies are a part of adaptive immunity.

Which of the following leukocytes functions as an antigen presenting cell?

Macrophage - Leukocytes (white blood cells) function as antigen presenting cells when they present antigens to adaptive immune cells for an adaptive immune response. Macrophages and dendritic cells are the main antigen presenting cells in the body. - Basophils and eosinophils are leukocytes that are known for having granules, which are released to kill pathogens and induce inflammation. - Neutrophils are the most abundant type of leukocyte and work to mainly phagocytose pathogens. - Lymphocytes are B cells, T cells, and natural killer cells. B and T cells are part of the adaptive immune response and natural killer cells target virally infected cells or cancer cells. B cells can act as antigen-presenting cells, but not all lymphocytes can. *Macrophages and dendritic cells are antigen presenting cells. Lymphocytes are B cells, T cells, and NK cells.

Which of the following most accurately describes a function performed by complement system proteins?

Membrane attack complex formation - Complement system proteins mainly tag pathogens for phagocytosis, amplify the inflammatory response by binding to mast cells for histamine release, and create the membrane attack complex (MAC) to create holes in pathogen membranes. *Interferons are secreted by cells that are virally infected and signals to non-infected cells to prepare them for a virus attack

5 Classes of antibodies you need to know for DAT: *Ig = immunoglobulin

Mnemonic: Me And Eve Don't Go 1. IgM - Pentamer (the only pentamer out of the 5 classes of antibodies) — contains 5 Y-shaped forks in one IgM -- Hence, IgM is the largest antibody! -- Think of IgMost because IgM has the most number of Y shaped monomer forks - First to be produced in response to an antigen - Activates complement system (innate immunity) 2. IgA - Dimer -- *Tip: when you think of IgA, think of IgAnd, when there is this and that —> dimer - Most abundant in body secretions e.g. breastmilk, tears, saliva -- Can give the newborn passive immunity through breastfeeding - Functions to bind and stop pathogens externally before they enter circulation 3. IgE - Monomer - These are antigen receptors found on basophils and mast cells -- Whenever there is an allergen, IgE will bind and trigger the release of histamine from these two cells → allergic reaction - *Tip: IgE stands for IgEve, Eve is one girl (monomer) who is allergic to many things. 4. IgD - Monomer - The function is not well understood, and only a small amount is produced - *Tip: IgD stands for IgDon't, as we don't know much about it! 5. IgG - Monomer - Most abundant antibody found in circulation e.g. blood, lymph - The ONLY antibody that can cross the placenta to give fetus passive immunity -- *Tip: IgG stands for IgGo, so it can go through the placenta! - Triggers opsonization = Binds to antigen and triggers phagocytosis - Also activates complement system

*DAT Mnemonic: inflammatory response → SLIPR:

Swelling Loss of function Increased heat Pain Redness

In cases of autoimmune diseases:

There are also cases of autoimmune diseases when the immune system mistakenly attack self cells, such as in type I diabetes when the pancreatic cells are destroyed by the immune system and lose their functions. Earlier, we talked about two kinds of antigen-presenting cells (APCs) that act as a bridge between the innate and adaptive response — macrophages and dendritic cells. In addition to MHC I molecules that all nucleated body cells bear, APCs specifically also have another type of MHC — MHC II — on their cell surface. After APCs phagocytose the pathogen and break off the antigen, APCs will load the antigen on the MHC molecule and present it to immune cells. For example, an immature T cell can bind to the antigen on the MHC II of the APC via its T Cell Receptor (TCR) and become activated. Note here that antigens can be presented on either MHC I or MHC II; later we will see how that makes a difference. There is an important part of the antigen called the epitope. The epitope is important because it is the section of the antigen that is recognized by immune cells (like B cells and T cells). Both B cells and T cells are lymphocytes, which means that they are produced from the bone marrow. They differ in that afterwards B cells stay and mature in the bone marrow, while T cells go and mature in the thymus.

Innate immunity - complement system (blood plasma proteins that participate in the innate immune response)

There are approximately 30 proteins included in the complement system. They are called the complement system because they are a system (group) of proteins that exist as a sidekick to the immune cell soldiers, helping the immune cells to make the battle against pathogens more effective. Although proteins are much smaller in size compared to cells, they can generate a big effect by 'turning each other on' through a cascade series of activation. They activate each other through the release of cytokines (intracellular signaling molecules).

Do you remember the third type of lymphocytes that we've talked about before in innate immunity?

They are the natural killer cells. They originate from the bone marrow but mature in many immune sites in the body, and eventually stay in the bloodstream.

Passive Immunity

This type of immunity is temporarily provided to an organism by the TRANSFER of active immunity components from one animal to another - that is, antibodies are GIVEN to the animal, rather than generated by that animal. Recall our lesson on B cells and antibodies, we talked about 5 classes of antibodies. Out of the 5, only IgG can cross the placenta, and IgA is found in body secretions such as milk. A fetus/newborn baby is IMMUNO-NAIVE, which means that they have not been exposed to the world with pathogenic microbes. Therefore, the fetus has not generated its own active immunity. This is where the mother steps in and protects the baby by PASSING DOWN her own antibodies to the fetus through the placenta (IgG) or breastfeeding (IgA). These antibodies will safeguard the baby until the infant generates their own active immune responses.

Innate immunity overview

We can think of the innate immune system as our body's frontline soldiers. These soldiers attack whenever there is enemy invasion. They are quick to act but lack specificity. Since they do not have a specific target, we describe the innate immunity as a NONSPECIFIC IMMUNE RESPONSE. The first layer of innate immunity are OUTER WALLS — physical and physiological barriers that prevent infection from entering the body. This is also the body's very first line of defence. Here's a list of the barriers found in our body: 1. Skin Thick epidermis, dermis, and hypodermis - Pathogens unable to penetrate through intact skin - Possesses mucous membranes -- Trap pathogens that do enter (for example, through a laceration/cut) and secrete lysozyme -- Lysozymes are antimicrobial proteins that are found in many types of body secretions, such as tears, saliva, and mucous. It is a type of enzyme that nonspecifically breaks down bacterial cell walls - Sebaceous glandsOil (sebum) itself serves as an additional physical barrierThe fatty acids in sebum possess antimicrobial properties 2. Cilia - These are little hair-like projections, which are found in the respiratory tract - They are like small brooms that sweep away unwanted guests that come in 3. Stomach Acid - Gastric acid kills many microbes with its low pH 4. Symbiotic Bacteria - Not all bacteria are bad! Symbiotic bacteria are our allies and out-compete their more hostile relatives -- We naturally have bacteria in our mouths (some of which are benign and don't cause an issue); if you take a steroid inhaler that kills those naturally occurring bacteria, you can end up with an opportunistic yeast infection (oral thrush)

Inactivation of the complement system would be caused by a deficiency in

complement regulatory proteins

after activation, B cells can differentiate into two types of cells with the assistance from helper T cells:

plasma cells and memory B cells.

Leukocytes:

white blood cells (WBCs)