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Five Classes of Antibodies
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Plasma cells make five classes of antibodies
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Immunoglobulins, or Igs (IgM, IgD, IgG, IgA, and IgE)
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Each type has antigenbinding sites and other sites with special roles
o Secreted Antibodies
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IgG: Main antibody in blood; activates complement,
neutralizes toxins; protects fetus and is secreted in early
milk
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IgA: Abundant in exocrine gland secretions (e.g., tears,
saliva, milk, mucus), where it occurs in the form. Interferes
with binding of pathogens to body cells
o Membrane-bound antibodies
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IgE: Anchored to surface of basophils, mast cells,
eosinophils, and some dendritic cells. IgE binding to
antigen induces anchoring cell to release histamines and
cytokines. Fact in allergies and asthma
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IgD: B cell receptor
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IgM: B cell receptor, as a monomer. Also is secreted as a
pentamer (group of five)
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What is an Antibody-Mediated Immune Response?
o In an antibody-mediated response, antibodies form and bind to
antigens of pathogens and toxins that are outside cells
o The steps that result in an antibody-mediated response produce
plasma cells, which make antibodies, and memory B cells
o Antibodies do not directly kill pathogens. They flag them for
destructions by other defenders
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o Plasma cells secrete five classes of antibodies (immunoglobulins)
that help protect the body against diverse threats.
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