Immunology

artificial passive immunity

Involves the injection of preformed specific antibodies When these antibodies are introduced into the person's body, the "loaned" antibodies help prevent or fight certain infectious diseases. The protection offered by passive immunization is short-lived, usually lasting only a few weeks or months. But it helps protect right away.

Mucous membranes

Mucous membranes consist of a layer of epithelial cells, that secrete mucus, which covers and protects the more fragile cell layers beneath it and traps debris and particulate matter, including microbes. In many regions of the body, mechanical actions serve to flush mucus in the respiratory system, inhalation can bring microbes, dust, and other small airborne debris into the body. This debris becomes trapped in the mucus lining the respiratory tract. The epithelial cells lining the upper parts of the respiratory tract are ciliated epithelial cells , movement of the cilia propels debris-laden mucus out and away from the lungs. The expelled mucus is then swallowed and destroyed in the stomach, or coughed up, or sneezed out. This system of removal is often called the mucociliary escalator.

Leukocytes of the innate immune system

Neutrophils Eosinophils Basophils Lymphocytes Monocytes

Neutrophils

Neutrophils are typically the first cells to arrive at the site of an infection because there are so many of them in circulation at any given time. Neutrophils are phagocytic cells that are also classified as granulocytes because they contain granules in their cytoplasm. These granules are very toxic to bacteria and fungi, and cause them to stop proliferating or die on contact. Like macrophages, they can move freely through the walls of veins and into the tissues of your body. Being highly motile, neutrophils quickly congregate at a focus of infection, attracted by cytokines expressed by activated endothelium, mast cells, and macrophages. Neutrophils express and release cytokines, which in turn amplify inflammatory reactions by several other cell types.

B cell activation action - T cell

Once a BCR binds a TD antigen, the antigen is taken up into the B cell through receptor-mediated endocytosis, degraded, and presented to T cells as peptide pieces in complex with MHC-II molecules on the cell membrane. T helper cells, that were activated with the same antigen recognize and bind these MHC-II-peptide complexes through their T cell receptor. Following TCR-MHC-II-peptide binding, T cells express the surface protein as well as cytokines. T cell-derived cytokines bound by B cell cytokine receptors also promote B cell proliferation, immunoglobulin class switching, and somatic hypermutation as well as guide differentiation. After B cells receive these signals, they are considered activated. Now activated, B cells participate in a two-step differentiation process that yields both short-lived plasmablasts for immediate protection and long-lived plasma cells and memory B cells for persistent protection

Cytotoxic T cells

Once activated, a cytotoxic T cell divides rapidly and produces an "army" of cells identical to itself. These cells travel throughout the body "searching" for more cells carrying their specific antigen. Whenever they encounter such cells, they destroy them. The cytotoxic T cell releases toxins, such as the protein perforin, that form pores, or holes, in the infected cell's membrane. T cell enzymes are then able to enter the infected cell and promote apoptosis, lysis or programmed cell death. The infected cell bursts, destroying both the cell and the viruses inside it. Perforin allows water and salts to enter, so the cell swells and bursts.

Opsonization

Opsonization is the second step of phagocytosis, with chemotaxis first causing the recruitment of the phagocyte towards the site of infection or cell death. Opsonins are molecules that mark foreign particles for phagocytosis. Opsonization, or the attachment of opsonins, then makes the pathogen more visible to the phagocyte, highlighting to other cells so they know it needs to be destroyed.

Macrophage

Originate from blood monocytes that leave the circulation to differentiate in different tissues. The ability to roam outside of the circulatory system is important, because it allows macrophages to hunt pathogens with less limits. Macrophages can also release cytokines in order to signal and recruit other cells to an area with pathogens.

Epitope

Part of an antigen that is recognized by the immune system, specifically by antibodies, B cells, or T cells. For example, the epitope is the specific piece of the antigen to which an antibody binds.

Passive immunity

Passive immunity doesn't require the body to make antibodies to antigens. The antibodies are introduced from outside the organism. Artificially acquired passive immunity is a short-term immunization by the injection of antibodies, such as gamma globulin, that are not produced by the recipient's cells. Naturally acquired passive immunity occurs during pregnancy, in which certain antibodies are passed from the maternal into the fetal bloodstream.

Natural active immunity

Production of one's own antibodies or T cells as a result of infection or natural exposure to antigen. E.g chicken pox virus and immunity develops following recovering from the disease as memory B cells are formed.

Artificial active immunity

Production of one's own antibodies or T cells as a result of vaccination against disease. A vaccine contains antigens from a pathogen, this stimulates the immune response and B lymphocytes will produce the complementary antibodies. Some divide to form memory cells for lasting protection. Sometimes booster injections are given to produce long term, more effective responses. Injection can be from dead pathogens, weak strains or antigens removed.

Antigen

Protein or carbohydrate chain of a glycoprotein within the plasma membrane that the body recognises as non-self. Pathogens have antigens, however antigens can also be part of a foreign human cell or cancer cell. Antigens are unique to that pathogen. A type of white blood cell called a lymphocyte recognizes the antigen as being foreign and produces antibodies that are specific to that antigen. Not all antigens will provoke a response. For instance, individuals produce innumerable "self" antigens and are constantly exposed to harmless foreign antigens, such as food proteins, pollen, or dust components.

Plasma cell

Short-lived antibody-producing cell derived from a B cell. B cells differentiate into plasma cells that produce antibody molecules closely modeled after the receptors of the precursor B cell. Once released into the blood and lymph, these antibody molecules bind to the target antigen and initiate its neutralization or destruction. Antibody production continues for several days or months, until the antigen has been overcome. Each plasma cell can secrete several thousand molecules of antibody, thus releasing a large amount of antibody into the circulation. The initial burst of antibody production gradually decreases as the stimulus is removed.

Steps of phagocytosis

Sometimes the immune cell accidentally bumps into a virus in the blood stream. Other times, cells move by way of a process called chemotaxis. The first step in phagocytosis is adhesion of the particle to be phagocytosed to the cell surface. This is facilitated by opsonization. The phagocyte then ingests the attached particle by sending out pseudopodia around it. These meet and fuse so that the particle lies in a phagocytic vacuole (also called a phagosome) bounded by cell membrane. Lysosomes, membrane-bound packets containing the toxic compounds described below, then fuse with phagosomes to form phagolysosomes. A phagolysosome is able to break down the inside of itself by drastically lowering the pH of its internal environment. Lowering the pH makes the environment inside the phagolysosome makes it very acidic.Once the contents have been neutralized, the phagolysosome forms a residual body that contains the waste products from the phagolysosome. The residual body is eventually discharged from the cell.

Phagocytosis

Specific form of endocytosis by which cells internalise solid matter, including microbial pathogens. While most cells are capable of phagocytosis, it is the professional phagocytes of the immune system, including macrophages, neutrophils and immature dendritic cells, that truly excel in this process. In these cells, phagocytosis is a mechanism by which microorganisms can be contained, killed and processed for antigen presentation.

T cells

T cell lymphocytes' continually scan and monitor cells for infection and the risk of infection. When a lymphocyte spots a cell that's been infected with bacteria or a virus, the lymphocyte will proceed to kill the cell and will actually remember the infectious agent, so it can act faster the next time it encounters the same infectious problem.

T cells activation

T cells are generated in the Thymus and are programmed to be specific for one particular foreign particle (antigen). Once they leave the thymus, they circulate throughout the body until they recognise their antigen on the surface of antigen presenting cells (APCs). T cell receptors can only recognize antigens that are bound to certain receptor molecules, Major Histocompatibility Complex on APCs. The T cell receptor (TCR) on both CD4+ helper T cells and CD8+ cytotoxic T cells binds to the antigen as it is held in a structure called the MHC complex, on the surface of the APC. This triggers initial activation of the T cells.

Memory T cells

T cells that remain from a proliferated clone after a cell-mediated immune response are called memory T cells. They circulate in the tissues, and should a pathogen with the same foreign antigen invade that body at a later date, thousands of memory cells are available to initiate a far swifter reaction than occurred during the first invasion.

Acquired immune response

The adaptive immune system uses specific antigens to strategically mount an immune response. Unlike the innate immune system, which attacks only based on the identification of general threats, the adaptive immunity is activated by exposure to pathogens, and uses an immunological memory to learn about the threat and enhance the immune response accordingly. The adaptive immune response is much slower to respond to threats and infections than the innate immune response, which is primed and ready to fight at all times. Specific defences usually last some time and is primarily by the action of B and T cells.

Action of antibodies

The antibodies inactivate antigens by, (a) complement fixation (proteins attach to antigen surface and cause holes to form, i.e., cell lysis), (b) neutralization (binding to specific sites to prevent attachment—this is the same as taking their parking space), (c) agglutination (clumping), (d) precipitation (forcing insolubility and settling out of solution)

Humoral response

The branch of acquired immunity that involves the activation of B cells and that leads to the production of antibodies, which defend against bacteria and viruses in body fluids that are circulating in the lymph or blood

classical complement pathway

The classical pathway begins with the formation of antigen-antibody complex (immune complex). This induces conformational changes in the Fc portion of the antibody which exposes a binding site for C1 protein. Proteins of the complement system then react with each other to form a macromolecular structure called the membrane attack complex (MAC). This makes hole in the bacterium, as a result, the intracellular contents leak out and unwanted substances get in. Thus, the cell cannot maintain its osmotic stability and the lysis occurs by an influx of water and loss of electrolytes. This is more effective in Gram negative bacteria than in Gram positive bacteria because MAC formation is easy in the outer membrane in Gram negatives whereas it is difficult in the rigid thick layer of peptidoglycan in Gram positives.

Complement system

The complement system is a set of over 20 different protein molecules always found in the blood. There are no cells in the system. With an infection, this system of molecules is activated, leading to a sequence of events on the surface of the pathogen that helps destroy the pathogen and eliminate the infection. The complement system can be activated in two main ways: part of the innate immune response, if certain polysaccharides found on the surface of bacteria activate the system (classical). The second and most potent (alternative) means occurs in a specific immune response when antibodies (IgG or IgM) binds to antigen at the surface of a cell. This exposes the Fc region of the antibody in a way that allows the first complement protein (C1) to bind. Thus the complement system works in both innate and acquired immunity.

humoral vs. cell-mediated immunity

The immune system distinguishes two groups of foreign substances. One group consists of antigens that are freely circulating in the body. These include molecules, viruses, and foreign cells. A second group consists of self cells that display aberrant MHC proteins. Aberrant MHC proteins can originate from antigens that have been engulfed and broken down (exogenous antigens) or from virus‐infected and tumor cells that are actively synthesizing foreign proteins (endogenous antigens).

Natural passive immunity

The immunity given to an infant mammal by the mother through the placenta and the colostrum. Preformed antibodies are obtained, providing short term protection, since the body is not stimulated to replicate and produce own antibodies/memory B-cells.

Antibody structure

The most common type of antibody, consists of 4 chains. There are 2 light chains and 2 heavy chains. The two heavy chains are bound together by a disulfide bond (S-S), and the two light chains are bound to the heavy chain by disulfide bonds. Together, they roughly form a Y shape. The variable regions (V), which make up the two identical antigen-binding sties, are different in each specific type of antibody, giving these sites specific shapes that fit certain antigenic epitopes. The remainder of the molecule consists of light and heavy chain constant regions (C) where these amino acid sequences vary little form antibody to antibody. The stability of the protein is crucially enhanced by naturally occurring disulfide cross-links.

Chemotaxis

The movement of leukocytes from the vessel lumen into into a damaged area is called chemotaxis and is mediated by substances known as chemotactic factors, that diffuse from the area of tissue damage. All granulocytes and monocytes respond to chemotactic factors and move along a concentration gradient (from an area of lesser concentration of the factor to an area of greater concentration of the factor). Chemoattractants can be exogenous (made by something other than the host's body) or endogenous (made by the body's own cells). Most exogenous chemotactic factors are bacterial or other microbial products (e.g., endotoxin).

alternative complement pathway

The pathway is triggered when the C3b protein directly binds a microbe. It can also be triggered by foreign materials and damaged tissues. his change in shape allows the binding of further plasma complement proteins in a cascade, to eventually form a membrane attack complex that pierces the membrane of the cell. This initiates a sequence of event leading to lysis (of a microbe) or apoptosis (of a cell of the body in pathologies and tissue transplants).

Cell-mediated response

The response of T-cells to antigen presentation.

Secondary response

The second time a person encounters the same antigen, there is no time delay, and the amount of antibody made is much higher. Thus, the secondary antibody response overwhelms the pathogens quickly and, in most situations, no symptoms are felt. When a different antigen is used, another primary response is made with its low antibody levels and time delay. If a second dose of the same antigen is given days or even years later, an accelerated 2° or anamnestic immune response (IR) occurs. This lag phase is usually very short (e.g. 3 or 4 days) due to the presence of memory cells. The amount of antibody produced rises to a high level. Antibody level tends to remain high for longer.

Autoimmunity

The state in which the immune system reacts against the body's own normal components, producing disease or functional changes. Normally, B/T lymphocytes that would trigger immune reactions to the body's own tissues are eliminated before they mature. Tissues bearing these autoantigens are generally safe from subsequent attack by the immune system unless either the autoantigen mutates or the immune system confuses the autoantigen with a foreign antigen. For reasons that are little understood, the elimination process sometimes fails, producing autoimmune disorders or diseases.

Stomach acid

The stomach produces acid which destroys many of the microbes that enter the body in food and drink. Low pH denatures enzymes within pathogens - cannot metabolise.

Skin

The topmost layer of skin, the epidermis, consists of cells that are packed with keratin. These dead cells remain as a tightly connected, dense layer of protein-filled cell husks on the surface of the skin. The keratin makes the skin's surface mechanically tough and resistant to degradation by bacterial enzymes. Fatty acids on the skin's surface create a dry, salty, and acidic environment that inhibits the growth of some microbes and is highly resistant to breakdown by bacterial enzymes. In addition, the dead cells of the epidermis are frequently shed, along with any microbes that may be clinging to them.

Agglutination

These interactions typically involve the binding of an antibody against an antigen and then further interactions between those antigen-antibody complexes with each other. Colloidal instability (the aggregation of the molecules into masses) can lead to precipitation of the antigen-antibody complexes. This increases the efficacy of microbial elimination by phagocytosis as large clumps of bacteria can be eliminated in one pass, versus the elimination of single microbial antigens.

TNF

Tumor necrosis factor-alpha (TNF-a) is the principle cytokine that mediates acute inflammation. Functions include acting on endothelial cells to stimulate inflammation and the coagulation pathway; stimulating endothelial cells and macrophages to produce chemokines that cause migration of leukocytes from the circulation to sites of inflammation or tissue injury, activating neutrophils and promoting extracellular killing by neutrophils and stimulating the endothelial cells that form capillaries to express proteins that activate blood clot formation within the capillaries. This occludes local blood flow to help prevent microbes from entering the bloodstream.

Nonspecific innate immunity

potential pathogens, which include viruses, bacteria, fungi, protozoans, and worms, are quite diverse, and therefore a nonspecific defense system that diverts all types of this varied microscopic horde equally is quite useful to an organism. The innate immune system includes: Physical Barriers - such as skin, the gastrointestinal tract, the respiratory tract, the nasopharynx, cilia, eyelashes and other body hair. Defense Mechanisms - such as secretions, mucous, bile, gastric acid, saliva, tears, and sweat. General Immune Responses - such as inflammation, complement, and non-specific cellular responses.

Helper T cells

Activated helper T cells do not kill pathogens or destroy infected cells, but they are still necessary for the immune response. In fact, they are considered to be the "managers" of the immune response. After activation, helper T cells divide rapidly and secrete cytokines. These chemical signals control the activity of other lymphocytes. Cytokines from helper T cells activate B cells to become produce plasma cells for antibody secretion and stimulate macrophages to phagocytise. They also activate other T cells. Most activated helper T cells die out once a pathogen has been cleared from the body. However, some helper T cells remain in the lymph as memory cells. These memory cells are ready to produce large numbers of antigen-specific helper T cells if they are exposed to the same antigen again in the future.

Active immunity

Activity immunity comes from exposure to a pathogen, this exposure to the antigen leads to the production of antibodies. This can occur when the person is exposed to a live pathogen, develops the disease, and becomes immune as a result of the primary immune response. Artificially acquired active immunity can be induced by a vaccine, a substance that contains the antigen. A vaccine stimulates a primary response against the antigen without causing symptoms of the disease.

Paratope

Also called an antigen-binding site, is a part of an antibody which recognizes and binds to an antigen. Each arm of the Y shape of an antibody monomer is tipped with a paratope, which is a set of complementarity determining regions.

Antigen presentation

An antigen-presenting cell (APC) is an immune cell that detects, engulfs, and informs the adaptive immune response about an infection. When a pathogen is detected, these APCs will phagocytose the pathogen and digest it to form many different fragments of the antigen. The fragments are then loaded onto MHC class I or MHC class II complex molecules (made from HLA proteins). Antigen fragments will then be transported to the surface of the APC plasma membrane, where they will serve as an indicator to other immune cells. Dendritic cells are immune cells that process antigen material; they are present in the skin and the lining of the nose, lungs, stomach, and intestines, ,macrophages also function as APCs and before activation and differentiation, B cells can also function as APCs.

Lyzozyme

An antimicrobial enzyme. Lysozyme is a glycoside hydrolase that catalyzes the hydrolysis of 1,4-beta-linkages between residues in peptidoglycan, which is the major component of gram-positive bacterial cell wall. This hydrolysis in turn compromises the integrity of bacterial cell walls causing lysis of the bacteria. Lysozyme is abundant in secretions including tears, saliva, human milk, and mucus. It is also present in cytoplasmic granules of the macrophages and the polymorphonuclear neutrophils (PMNs).

Antigenic variation

Antigenic variation is a process by which many infectious agents, including some pathogenic viruses, bacteria, fungi, and parasites, evade the defense responses of the vertebrate immune system. Pathogens that can periodically change or switch the molecular composition of their surface antigens. This periodic variation provides a means for individual organisms within a population to temporarily camouflage themselves and thereby prevent elimination of the entire population by the host's immune system. In some pathogens, antigenic variation is accomplished through random mutations in the genes encoding either surface molecules themselves or the enzymes that synthesize them. This will allow the pathogen to re-infect the host while the immune system generates new antibodies to target the newly identified antigen.

B cell activation

B cell activation begins by the recognition and binding of an antigen by the B cell receptor. This can either take place in a T cell dependent or T cell independent manner. One important difference between BCRs and TCRs is the way they can interact with antigenic epitopes. Whereas TCRs can only interact with antigenic epitopes that are presented within the antigen-binding cleft of MHC I or MHC II, BCRs do not require antigen presentation with MHC; they can interact with epitopes on free antigens or with epitopes displayed on the surface of intact pathogens. Another important difference is that TCRs only recognize protein epitopes, whereas BCRs can recognize epitopes associated with different molecular classes (e.g., proteins, polysaccharides, lipopolysaccharides).

B cells

B cell lymphocytes don't attack and kill cells, viruses or bacteria themselves. Instead, they manufacture proteins called antibodies that actually stick to the surface of invaders, disabling those invaders

B cell activation - direct

B cells possess antigen-specific receptors with diverse specificities. Although they rely on T cells for optimum (quicker) function, B cells can be activated without help from T cells. Activation of B cells without the cooperation of helper T cells is referred to as T cell-independent activation and occurs when BCRs interact with T-independent antigens. T-independent antigens (e.g., polysaccharide capsules, lipopolysaccharide) have repetitive epitope units within their structure, and this repetition allows for the cross-linkage of multiple BCRs, providing the first signal for activation. Once a B cell is activated, it undergoes clonal proliferation and daughter cells differentiate into plasma cells. After differentiation, the surface BCRs disappear and the plasma cell secretes pentameric IgM molecules that have the same antigen specificity as the BCRs. The T cell-independent response is short-lived and does not result in the production of memory B cells. Thus it will not result in a secondary response to subsequent exposures to T-independent antigens.

Antibodies

B lymphocytes give rise to plasma cells which produce antibodies. Antibodies are proteins that are capable of combining with and neutralising agents. They are secreted into the blood and lymph, where they are also known as gamma globulins. Antibodies are Y-shaped proteins with two arms. Each arm has a heavy polypeptide chain and a light polypeptide chain. These chains have constant regions, where the sequence of amino acids is set. As well as variable regions where the sequence varies. Constant regions are not identical among all antibodies, only those within the same class. The variable region forms the antigen binding site, with the specific structure complementary only to a specific antigen, forming an antigen-antibody complex. Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly. Antibodies coat extracellular pathogens and neutralize them by blocking key sites on the pathogen that enhance their infectivity, such as receptors that "dock" pathogens on host cells. complement cascade. Antibodies also mark pathogens for destruction by phagocytic cells, such as macrophages or neutrophils, because they are highly attracted to macromolecules complexed with antibodies (opsonisation).

Basophils

Basophils are also granulocytes that attack multicellular parasites. They are the only circulating leukocytes that contain histamine, thus their physiological role is thought to be the release of cytokines, leukotrienes and histamine to aid immunity to pathogens. These chemicals have a number of effects, including constriction of the smooth muscles, which leads to breathing difficulty; dilation of blood vessels, causing skin flush and hives; and an increase in vascular permeability, resulting in swelling and a decrease in blood pressure.

Agglutination vs precipitation

Both reactions are highly specific because they depend on the specific antibody and antigen pair. The main difference between these two reactions is the size of antigens. For precipitation, antigens are soluble molecules, and for agglutination, antigens are large, easily sedimented particles. It takes a lot of more soluble antigens and antibody molecules to form a visible precipitation than agglutination.

Immune system

the complex group of defense responses found in humans and other advanced vertebrates that helps repel disease-causing organisms (pathogens). Immunity from disease is actually conferred by two cooperative defense systems, called nonspecific, innate immunity and specific, acquired immunity.

Chemokines

Chemokines are signaling proteins secreted by cells of the immune system that stimulate the movement of other cells. Their name is reminiscent of their function since it is derived from chemotaxis, or movement in response to a chemical stimulus. Inflammatory chemokines function mainly as chemoattractants for leukocytes, recruiting monocytes, neutrophils and other effector cells from the blood to sites of infection or tissue damage. Some chemokines control cells of the immune system during processes of immune surveillance, such as directing lymphocytes to the lymph nodes so they can screen for invasion of pathogens by interacting with antigen-presenting cells residing in these tissues. These are known as homeostatic chemokines and are produced and secreted without any need to stimulate their source cell.

Phagocyte

Circulate throughout the body, looking for potential threats, like bacteria and viruses, to engulf and destroy.

Commensal bacteria

Commensal gut bacteria have many beneficial effects for the host, includ- ing competition with pathogens for nutrients, preventing their establishment

Primary response

the primary response to an antigen (representing a pathogen) is delayed by several days. This is the time it takes for the B cell clones to expand and differentiate into plasma cells. The level of antibody produced is low, but it is sufficient for immune protection. The lag phase can be as short as 2-3 days, but often is longer, sometimes as long as weeks or months, and the amount of antibody produced is usually relatively low.

Saliva

Contains antimicrobial enzymes that kill bacteria including lysozyme and maintains an anti-bacterial ph in the mouth.

Cytokines

Cytokines are a diverse family of small proteins or glycoproteins that are released from one cell affect the actions of other cells by binding to receptors on their surface. Influencing both innate and adaptive immune responses, the two principal producers of cytokines are helper T cells (Th cells) and macrophages. There are different types of cytokines, including chemokines, interferons, interleukins, lymphokines and tumour necrosis factor, all help to regulate the immune response.

Dendritic cells

Dendritic cells are monocytes that have migrated to cells that are in contact with the external environment, such as the skin, intestines, or respiratory epithelium. Their name comes branched projections called dendrites, which increase their surface area. They phagocytize pathogens and present antigens to naive lymphocytes.

Lymphocytes

Determine the specificity of the immune response to infectious microorganisms and other foreign substances. Two primary types of lymphocytes are B lymphocytes and T lymphocytes, or B cells and T cells. Each lymphocyte bears receptors that bind to a specific antigen. The ability to respond to virtually any antigen comes from the enormous variety of lymphocyte populations that the body contains.

Memory b cells

First exposure to a microbe or an antigen, leads to the activation of naive B lymphocytes. These B cells differentiate into antibody-producing plasma cells and memory cells. As the primary response terminates, memory B cells often take up residence in a body location where the antigen might next be expected to attack. For example, in response to an antigen first encountered in a lymph node, some of the memory B cells produced remain in the follicular mantle and are ready to react rapidly when a fresh dose of the antigen is conveyed to the lymph node. However, other memory B cells may leave the original lymph node and enter the blood, circulating among the body's chain of lymph nodes and maintaining peripheral surveillance for the antigen. They persist in the absence of antigens but do not produce antibodies (i.e., do not protect), unless reexposure to antigen drives their differentiation into antibody-producing plasma cells. Memory B cells are clones of a parent B cell that previously served as an antigen-presenting cell and then activated by a helper T cell to proliferate. As clones, the memory B cells bear the same B cell receptors as those of the parent B cell. Therefore, they would be able to detect the same antigen when re-exposed. Memory B cells produce more robust antibody-mediated immune response during re-infection.

Precipitation of antibodies

For precipitation, antigens are soluble molecules. Precipitation is the formation of an insoluble molecule in a liquid solution; this insoluble molecule is called the precipitate. A precipitate is formed when two soluble ionic compounds are mixed. Soluble ionic compounds can break into their ions in the solution. Then these ions can react with each other to form a precipitate or stay as a solubilized ion in that solution. Antibodies (precipitins) attach to soluble toxins (antigens) and they group together. This neutralises the action of the toxin molecule.

Eosinophils

Granulocytes target multicellular parasites. Eosinophils secrete a range of highly toxic proteins and free radicals that kill bacteria and parasites. Eosinophils, along with basophils and mast cells, are also important mediators of allergic responses and asthma pathogenesis

Interleukin-1 (IL-1)

IL-1 function similarly to TNF in that it mediates acute inflammatory responses. It also works synergistically with TNF to enhance inflammation. Functions of IL-1 include promoting inflammation ; activating the coagulation pathwa (blood clotting), catabolism of fat for energy conversion, inducing fever and sleep; stimulates the synthesis of adhesion factors on endothelial cells and leukocytes for diapedesis ; and activates macrophages.