Antibody Function Flashcards
Affinity
Describes the strength of the interaction between an antigen-binding site and an antigen. An antibody with high affinity for antigen binds to the antigen tightly.
Avidity
Describes the strength of the interaction between antibodies and an antigen, when multiple antigen binding sites are being utilized. For example, a pentameric IgM molecule has ten antigen binding sites as compared to a monomeric IgG molecule that has two.
Class switching
After the initiation of a memory immune response, B cells undergo class switching. Class switch recombination (CSR) is the process by which the constant region of the immunoglobulins being produced by a B cell change, while the variable region that determines the antigenic specificity is maintained. CSR is necessary to produce IgG, IgA, and IgE antibodies.
Neutralization
The process through which certain antibodies can inhibit the infectivity of a virus or the toxicity of a toxin. Such “neutralizing antibodies” function by binding to strategic epitopes (antigenic determinants) on the virus or toxin and preventing them from entering cells.
Fc receptor
This type of transmembrane protein receptor can be found on macrophages, neutrophils, NK cells, and mast cells (among other cell types), and is used to bind the Fc portion of the immunoglobulins. The Fc receptors help to facilitate opsonization as well as antibody-dependent cell-mediated cytotoxicity (ADCC). The Fc receptors can be specific to a particular Ig isotype, such as Fc-gamma receptor (for IgG) and Fc-epsilon (for IgE).
Opsonization
Opsonization occurs when proteins bind to an antigen to tag it for phagocytosis bu neutrophils or macrophages. Antibodies and complement are the most common proteins that opsonize antigens. IgG is the most important antibody for opsonization. While opsonization primarily focuses on the elimination of bacteria; viruses (that have not gained access into cells) as well as other microbes may also be targeted for opsonization.
Natural Killer (NK) Cells
Large, granular, non-B, non-T lymphocytes which function in innate immune responses to kill microbe-infected cells and some tumor cells. NK cells do not express antigen-specific receptors (BCR or TCR); instead, their activation is regulated by a combination of cell surface stimulatory and inhibitory receptors. The inhibitory receptors on NK cells recognize self MHC molecules. The stimulatory receptors recognize molecules present or upregulated on cells during viral infections.
Apoptosis
A process of cells death affecting single cells, marked by cell shrinkage, DNA cleavage, nuclear condensation and fragmentation, plasma membrane blebbing, and fragmentation of the cell into membrane-bound apoptotic bodies that are eliminated by phagocytosis, thereby eliminating the cell without inducing an inflammatory response. This type of cell death is a normal process in the body, playing an essential role in lymphocyte development, regulation of lymphocyte responses to foreign antigen, and maintenance of tolerance to self antigens, as well as mediating the elimination of cells with damaged DNA.
Mast Cell
The major effector cell of immediate hypersensitivity reactions. Mast cells are derived from bone marrow, reside in most tissues, express a high affinity Fc receptor for IgE, and contain numerous granules filled with mediators such as histamine and cytokines. Antigen-induced cross-linking of IgE on the mast cell surface causes release of the granule contents, producing many of the clinical signs of immediate-type hypersensitivity (allergy).
Helminth
A parasitic worm. Helminthic infections often elicit Th2-regulated immune responses characterized by eosinophil-rich inflammatory infiltrates and IgE production.
Complement
A system of serum and cell surface proteins that generate important effectors of innate and adaptive immune responses through a cascade of interactions with one another and with other molecules of the immune system. The classical pathway of the complement system is activated by the formation of antigen-antibody complexes, while the alternative pathway is initiated on microbial cell surfaces in the absence of an antibody. There is also a third pathway of complement activation, the lectin pathway. All three of the complement pathways consist of a cascade of proteolytic enzymes that generate inflammatory mediators and opsonins, and all pathways can lead to the formation of a Membrane Attack Complex that mediates cell lysis. All complement proteins lie inactive in the blood until activated by one of the complement pathways.
Chemoattractants
Molecules that mediate chemotaxis, the attraction of cells directed by a concentration gradient. Various cytokines and complement molecules can act as chemoattractants for lymphocytes and other leukocytes.
Transcytosis
Transcytosis is the process by which a molecule is transported across the interior of a cell. While it is very common across the epithelium, it also occurs elsewhere in the body. Polymeric IgA is transported to mucosal surfaces via transcytosis.
Secretory component
The proteolytically cleaved portion of the extracellular domain of the poly-Ig receptor that remains bound to an IgA molecule in mucosal secretions
