Antibody-antigen reactions:
A reaction that take place between antigens and antibodies are used as defence mechanisms:
i) Complement fixation and activation
• used primarily against bacteria and mismatched red blood cells (after transfusion)
• after antibodies binding to target/receptor change shape expose complement binding sites complement fixation cell lysis
• also promote phagocytosis due to opsonisation
ii) Neutralisation
• antibodies block specific sites on viruses or bacterial toxins prevent binding to receptor sites prevents tissue damage antibody-antigen complex is eventually phagocytosed
iii) Agglutination
• antigen-antibody complexes can cross link form larger ‘clumps’ (agglutination)
• IgM has 10 antigen binding sites potent agglutinating agent
• occurs when mismatched blood cells are transfused and forms the basis of the test for blood typing
iv) Precipitation
• soluble molecules, after binding with antigen settle out of solution more easily phagocytosed.
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