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Serology. Introduction. The immune responses refer to the ability of the body (self) to recognize specific foreign factors (non self) that threaten its biological integrity. There are two major branches of the immune responses:
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Introduction • The immune responses refer to the ability of the body (self) to recognize specific foreign factors (non self) that threaten its biological integrity. There are two major branches of the immune responses: • Humoral immunity (the production of antibody molecules in response to an antigen; mediated by B-lymphocytes). • cell-mediated immunity (the production of cytotoxic T-lymphocytes and cytokines in response to an antigen; mediated by T-lymphocytes).
An antigen: is macromolecule that can trigger the formation of antibodies or sensitized cells in an immunocompetent host. • Antigen are composed of proteins, carbohydrate, lipid and nucleic acid or combination of any of these. • Immunogen: is any substance that is capable of inducing immune response. • All immunogen are antigen but not vice versa. • Factors involved in immunogenicity • Macromolecular size (MW at least 10.000), Chemical composition (proteins and polysaccharides are the best immunogen), Molecular complexity, Foreignness.
Epitopes or antigenic determinants: The actual portions or fragments of an antigen that react with receptors on B-lymphocytes and T-lymphocytes (Key portion of the immunogen), as well as with free antibody molecules. • The number of epitope per molecular is called valence. • The size of an epitope is generally thought to be equivalent to 5-7 amino acids or 3-4 sugar residues. • Haptens: Are small substances, so the are nonimmunogenic material but, when combine with a carrier, create new antigenic determinants and are then able to stimulate a response.
Antibodies or immunoglobulins: which are synthesized and secreted by plasma cells in response to foreign antigen. • The Fab portions provide specificity for binding an epitope on an antigen. • The bottom part of the "Y" is called the Fc portion and this part is responsible for the biological activity of the antibody.
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There are 5 classes of human antibodies: IgG, IgM, IgA, IgD, and IgE. • IgG: 75-80% of total serum immunoglobulin's, half-life = 23-25 days, is the better at precipitation than agglutination because precipitation involves soluble particles. • IgM: 5-10% of total serum immunoglobulin's, half-life = 10 days and much more efficient at agglutination.
Serology: refers to using antigen-antibody reactions in the laboratory for diagnostic purposes. • Two distinct ways: • Direct serologic testing: to identify unknown antigens such as microorganisms • Indirect serologic testing: to detect antibodies being made against a specific antigen in the patient's serum
Direct serologic testing • This type of serologic testing employs known antiserum (serum containing specific known antibodies). The preparation of known antibodies is prepared in one of two ways: • Preparation of known antisera in animals. • Preparation of known antibodies by monoclonal antibody technique. • Antigen-antibody reactions may be detected in the laboratory by a variety of techniques.
Agglutination • Antigens may be: • On a cell (direct agglutination). • Attached to latex spheres (indirect or passive agglutination).
Precipitation Involve soluble antigens with antibodies
No Ag Ag Patient’s serum Y Y Y Y Y Y Y Y Y Y Complement-fixation • Standard amount of complement is added Ag mixed with test serum to be assayed for Ab • Erythrocytes coated with Abs is added • Amount of erythrocyte lysis is determined Ag Ag
