Quantifying Antigen-Antibody Reactions
1. Active immunity occurs naturally in response to infections or other natural exposure to antigens, and artificially in response to vaccination.
1. Passive immunity occurs naturally during pregnancy and through breast feeding, and artificially by transfer of preformed antibodies, as in immune serum globulin and hyperimmune globulin.
1. A vaccine is a preparation of a disease-causing agent or its products used to induce active immunity. It protects an individual against disease, and can also provide herd immunity. (Table 17.1)
1. An attenuated vaccine is a weakened form of the disease-causing microorganism or virus that can replicate but is generally unable to cause disease.
1. Inactivated vaccines are unable to replicate but they retain the immunogenicity of the infectious agent or toxin. They include inactivated whole agents, toxoids, protein subunits, purified polysaccharides, and polysaccharide-protein conjugates.
2. Adjuvants increase the intensity of the immune response to the antigen in a vaccine.
An Example of Vaccination Strategy-The Campaign to Eliminate Poliomyelitis
1. Both the Sabin and the Salk polio vaccines protect against paralytic poliomyelitis; only the Sabin vaccine induces mucosal immunity.
The Importance of Routine Immunizations for Children (Table 17.3)
1. Routine childhood immunizations have prevented millions of cases of disease and many deaths during the past decades.
1. Progress in vaccination includes enhancement of the immune response to vaccines, development of new or improved vaccines against certain diseases, and development of new types of vaccines. (Table 17.5)
1. Serology uses antibodies, usually in serum or other body fluids, to detect and identify antigens, or conversely, uses known antigens to detect antibodies.
1. The change from negative to positive for specific antibodies during an infection is seroconversion; a rise in titer is characteristic of an active infection.
2. Serial dilution of specimens permits quantification of antibodies in the sample.
1. Precipitation occurs when soluble antigens interact with antibodies in optimal proportions to cause cross-linking into a large insoluble lattice. (Figure 17.3)
1. Precipitation tests are done in gels where the precipitate can be readily seen. (Figures 17.4,17.5)
Immunoelectrophoresis (Figure 17.6)
1. In immunoelectrophoresis, mixtures are separated by electrophoresis before the addition of antibodies to identify the separated antigens.
17.5 Agglutination Reactions
1. Agglutination tests depend on cross-linking of particulate antigen by antibody molecules to form readily visible clumps. (Figure 17.7)
Direct Agglutination Tests
1. Particulate antigen reacts directly with antibodies.
Indirect Agglutination Tests
1. Soluble antigen is coated onto particles to give indirect agglutination.
1. Antibodies interfere with viral agglutination of red blood cells.
17.6 Immunofluorescence Tests
1. Fluorescent dyes are used to visualize antibodies under the fluorescence microscope. (Figure 17.8)
Direct Fluorescent Antibody Test
1. Antibodies tagged with fluorescent dyes react directly with antigen.
1. Antigen and antibody interact, and the resulting complex is detected with fluorescent-labeled antibodies against the immunoglobulin in the complex.
17.7 Radioimmunoassay (RIA), Enzyme-Linked Immunosorbent Assay (ELISA), and Western Blot
1. RIA, ELISA, and Western blot tests are extremely sensitive and efficient.
1. RIA is based on competition for specific antibody in a test sample between known amounts of radioactively labeled antigen and unknown amounts of unlabeled antigen.
2. Concentration of the unknown is determined by comparison with a standard curve.
Enzyme-Linked Immunosorbent Assay (ELISA)
1. Enzymes that give a color reaction are used as labels in the ELISA test. (Figure 17.9)
1. The Western blot technique combines electrophoresis with ELISA to separate and identify protein antigens in a mixture. (Figure 17.11)
17.8 The Complement Fixation Test and Neutralization Tests
1. The complement fixation test measures the binding of complement by an antigen-antibody interaction, using an indicator system. (Figure 17.12)
Review Questions 439
2. Antibodies neutralize viruses or toxins in neutralization tests.
17.9 Tests Used in Cellular Immunology
Identification of Subsets of Lymphocytes
1. Fluorescent-labeled monoclonal antibodies will distinguish subsets, either by microscopy or by separation in a cell sorter.
Lymphocyte Response to Mitogens
1. A variety of substances that stimulate cellular proliferation can distinguish subsets of lymphocytes.
Cytotoxic T-Cell Function
1. Release of radioactive chromate from target cells measures killing by Tc cells.
Cell-Mediated Immunity to Infectious Agents
1. Lymphocyte proliferation in response to specific antigens is measured by incorporation of radioactive thymidine into DNA.
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