Exam 3 Review: Chapter 21: Antibody-Mediated Immunity
immunoglobulin = antibody - Any of a group of large glycoproteins which are secreted by plasma cells in response to a specific antigen and which function in the immune response by binding with specific antigens; there are five classes of immunoglobulins: IgA, IgD, IgE, IgG, and IgM; these proteins carry a net positive charge at body fluid pH and are found in the gamma fraction of the plasma proteins; the molecule is composed of four polypeptide chains — two identical light chains and two identical heavy chains — joined by disulfide bridges; each type of chain has a constant and a variable portion that is different in each type of antibody and is the active portion of the molecule which binds with the specific antigen; the immune functions of different classes of antibodies are determined by properties of the constant regions of the heavy chain; immune functions include binding the antigen, neutralizing toxins, removing substances from circulation in body fluids; agglutinating cellular antigens; and activating complement (blood serum proteins which cause the destruction of invading cells). See the structural diagram below:
antigen presenting cell - Those monocyte-derived wandering and fixed macrophages capable of partially digesting foreign matter and placing derived antigenic determinants on their cell surfaces in conjunction with MHC Class II surface markers in order to expose responsive B and T lymphocytes in order to activate them.
antigen processing - The part of the process of antigen presentation in which the macrophage has engulfed the foreign material, partially degraded it by enzymatic attack in the phagolysosome, and passed the mix of antigenic determinants to various MHC Class II markers which bind them and transport them to the cell surface of the macrophage so that it can expose responsive B and T lymphocytes in order to activate them.
antigen binding site (on antibody) - The subregion of the variable portion of the antibody molecule which is capable of specific noncovalent (reversible) binding to the antigenic determinant as a result of attraction and fit between the antigen binding site and a portion of he antigenic determinant; recognition and binding is due to compatible size, shape and surface charge characteristics.
antibody heavy chain - The larger longer pair of identical polypeptide chains which are covalently linked to each other and to the corresponding light chains by disulfide bridges; each heavy chain consists of three constant portions and a variable portion; the variable portion, along with the variable portion of the corresponding light chain form the antigen binding site; components of the constant portions determine specific immune functions. e.g., complement fixation, secretion to mucous membranes, opsonization, phagocytosis, and are used in separating antibodies into five classes: IgA, IgD, IgE, IgG, and IgM.
antibody light chain - The smaller shorter pair of identical polypeptide chains which are covalently linked to the corresponding light chains by disulfide bridges; each light chain consists of a constant portion and a variable portion; the variable portion, along with the variable portion of the corresponding heavy chain form the antigen binding site. See the structural model below in which the heavy chains are depicted in red and the light chains in yellow:
antibody constant regions - Those portions of the light and heavy chains of immunoglobulin molecules which are responsible for giving shape to the molecule in regions other than the antigen binding site; these portions of the heavy chain are responsible for determining specific immune functions and are used in separating antibodies into five classes: IgA, IgD, IgE, IgG, and IgM.
antibody variable regions - Those portions of the light and heavy chains of immunoglobulin molecules which are responsible for giving shape, surface charge, and functional (bonding) properties to the antibody molecule in the antigen binding site. See the structural diagram below:
primary (immune) response - The initial response of the immune system to a first encounter with a foreign antigen in which there is a delay of several days (from one to three weeks) before any significant immune defenses are evident; the delay is due to the time required for macrophages to encounter, phagocytize, and process the foreign antigen, followed by the time required for the macrophages to locate suitable antigen-specific T and B lymphocytes for antigen-presentation, and followed by the time required for lymphocytes to become activated and to proliferate into functional clones capable of generating specific responses, e.g., antibody production, against the foreign antigen.
secondary (immune) response - The rapid response of the immune system to a second or subsequent encounter with a foreign antigen in which there is little delay (a few minutes to several hours to a few days before any significant immune defenses are evident; the lack of delay is due to the availability of T and B memory lymphocytes which can respond almost immediately to antigen-presenting macrophages, and the ability of these stimulated memory lymphocytes to become activated and to proliferate into functional clones capable of generating specific responses, e.g., antibody production, against the foreign antigen.
Sketch and label:
1. The structure of an antibody.
|
||
 |
2. The process of antigen processing and display. How does this process
differ for endogenous versus exogenous antigens?
| Endogenous antigen (from virally-infected cells or tumor cells) is processed by the self cell in conjunction with the participation of MHC Class I (HLA or tissue typing) self-cell surface markers. This combination of the MHC Class I marker and the "foreign" antigen helps the immune cells "understand" that a self cell will need to be attacked. A macrophage may not even be involved. |
 |
| Exogenous antigen (foreign antigens, e.g., viruses, microorganisms, venoms, toxins, or drugs, etc.) is processed by a macrophage in conjunction with the participation of MHC Class II self-cell surface markers. MHC Class II markers, which have a limited distribution on macrophages, lymphocytes, and a few other cells, helps the specific immune cells (macrophages, B lymphocytes and T lymphocytes) recognize and cooperate with one another in developing specific defenses against the foreign antigen. |
 |
| Once processed, the endogenous antigen is displayed on the self cell surface in conjunction with the MCH Class I marker in a complex. That complex is recognized by various immune cells, most often by antigen-specific cytotoxic Tc lymphocytes which will then release various immune defensive compounds in an effort to destroy the virally-infected cells or tumor cells. |
 |
| Once processed, the exogenous antigen is displayed on the macrophage surface in conjunction with the MCH Class II marker in a complex. That complex is recognized by various immune cells, most often by antigen-specific helper Th lymphocytes and B lymphocytes. The helper Th lymphocytes will then release various immune regulatory compounds (e.g., interleukins) which will serve to activate and cause proliferation of the antigen-specific cytotoxic Tc lymphocytes and B lymphocytes. The activated cytotoxic Tc lymphocytes will then seek out the foreign cellular antigen (e.g., viruses, microorganisms, parasites) and attempt to kill them. At the same time, the activated B lymphocytes become plasma cells which secrete specific antibodies which will bind with the foreign antigen (e.g., viruses, microorganisms, venoms, toxins, or drugs, etc.) and trigger the variety of antibody-mediated immune defenses against the foreign antigen. |
 |
| How does this process differ for endogenous versus exogenous antigens? The two key differences are (1) endogenous antigen processing does not require the involvement of a macrophage while exogenous antigen processing does require a macrophage; and (2) endogenous antigen processing requires the recognition of specific MHC Class I (HLA or tissue typing) self-cell surface markers which are widely distributed (on most cell types other than erythrocytes) while exogenous antigen processing requires the recognition of specific MHC Class II cell surface markers which are narrowly distributed and found primarily on macrophages and lymphocytes. |
