Page 476 - Veterinary Immunology, 10th Edition

in the previous chapter. These receptors are, however, not restricted
VetBooks.ir to the B cell surface. Once a B cell response is triggered, it becomes

a plasma cell and its antigen receptors are produced in huge
amounts and shed into the surrounding fluid where they act as

antibodies. These antibodies bind to foreign antigens and mark
them for destruction or elimination. Antibodies are found in many
body fluids but are present in highest concentrations and are most
easily obtained from blood serum. Antibodies have to defend an

animal against many different types of microbes, including bacteria,
viruses, helminths, and protozoa. They must also act in several
different environments, for example, in blood or milk, or on body
surfaces. It is not surprising, therefore, that multiple

immunoglobulin classes exist. Each class is optimized for action in a
specific environment; for instance, IgA protects body surfaces.
Immunoglobulins may also be optimized for activity against a
specific group of pathogens. For example, IgE is important in the

defense against parasitic worms.

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