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Antigens and Antibodies

Introduction

            Immunity--state of resistance to a specific pathogen

                        Acquired immunity--initial exposure required

                                    Immune system activated by microbes or viruses

                                                animal cells

                                                viruses

                                                toxins (toxoids)

                                                bacteria

                                                vaccines

 

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

            Responses:

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

protein

                        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

        antigen

                        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

                                    Bacterial

                                                Exotoxins and enzymes

                                                Structural components

                                                            Polysaccharide-phospholipid-protein

                                                                        Antigen O--somatic antigen

                                                                                    Gram- :  enteric bacilli

                                                                                    Gram+ :  Lancefield group

                                    Viral

                                                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

                        Types:

                                    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

specificity

            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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