Antigens and Antibodies


            Immunity--state of resistance to a specific pathogen

                        Acquired immunity--initial exposure required

                                    Immune system activated by microbes or viruses

                                                animal cells


                                                toxins (toxoids)




Antigen--any substance which provokes an immune response in host


1)      formation of antibodies (humoral immunity)

2)      proliferation of lymphocytes (cell mediated immunity)

Properties of antigens

            Foreign chemicals elicit immune response

            Immunogenic compounds

                        Proteins--more effective in stimulating response

                        Polysaccharides--large complexes:  strong response

                        Haptens--Oligosaccharides, lipids, or nucleic acids combined with


                        Physical characteristics

                                    soluble substances--bacterial toxins, serum proteins

                                    particulate matter--bacterial cell, virion

                                                more immunogenic

                                    M.W.>10000 daltons

            Antigenic determinants--reactive sites--specificity

                        Antigen may have 2 to 200 antigenic determinants

                        Species have unique and common antigenic determinants

                                    Heterophile antigens--elicit antibodies capable of reacting with

tissues of a wide variety of unrelated animals

            Adjuvants--substances which increase antibody production when combined with


                        Alum, aluminum salts, endotoxins, water/oil emulsions

            Naturally occurring antigens

                        Human tissue antigens

                                    ABO blood groups

                                                isoantibodies (same species)

                                    Rh complex blood group antigen system

                                                erythroblastosis fetalis

                                                female--Rh negative:  male--Rh positive

                                    Autoimmune diseases--malfunction

                                    Histocompatibility antigens


                        Bacterial and Viral antigens


                                                Exotoxins and enzymes

                                                Structural components


                                                                        Antigen O--somatic antigen

                                                                                    Gram- :  enteric bacilli

                                                                                    Gram+ :  Lancefield group


                                                Protein capsid (lipoprotein, glycoprotein)

                                    Vaccines--suspension of killed/attenuated microbe

                                                Typhoid fever vaccine--killed Salmonella sp

                                                Salk poliomyelitis vaccine--killed virus

                                                Sabin poliomyelitis vaccine--attenuated

                                                Toxoid vaccines--toxic portion deactivated


Antibodies--specific substances formed in response to antigenic stimulation

            Serum protein--immunoglobulin (Ig)

            Classes of Immunoglobulins

                        Five classes of similar structure

                                    Two light and two heavy polypeptide chains

                                                Disulfide bonds bind polypeptides

                        Unique amino acid sequences--specify type (heavy chain)

                        Light chains--kappa and lambda


                                    IgG--70%;  transplacental;  newborn protection

                                    IgM--6%;  multimeric (J chain);  microbial

                                    IgD--1%;  regulator of synthesis ?

                                    IgA--10%;  dimmers;  body secretions;  1st defense

                                    IgE--.002%;  allergic response;  histamines/HT-5

                        Antigen binding site--terminal end of light and heavy chain determines


            Functional names of antibodies (humoral) specificity

                        Antitoxins--neutralize toxins

                        Agglutinins--clumping of bacterial cells

                        Precipitins--flocculation of bacterial extracts

                        Lysins--bacterial lysis

                        Complement fixing--antibody/antigen/complement complex

                        Opsonins--increase susceptibility to phagocytosis

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