Page 251 - Veterinary Immunology, 10th Edition

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FIG. 9.1 The structure of a typical bacterium and the location of its
most important antigens.

Bacterial capsules consist mainly of polysaccharides that are

usually good antigens. The capsules protect bacteria against
phagocytosis and intracellular destruction, whereas anticapsular
antibodies can overcome the effects of the capsule and protect an

infected animal. Capsular antigens are collectively called K
antigens.
Pili and fimbriae are short projections that cover the surfaces of
some Gram-negative bacteria; they are classified as F or K antigens.
Pili bind bacteria together and play a role in bacterial conjugation

and movement. Fimbriae bind bacteria to cell surfaces. Antibodies
to fimbrial proteins may be protective since they can prevent
bacteria from sticking to body surfaces. Bacterial flagella are long

filaments used for bacterial movement. They consist of a single
protein called flagellin. Flagellar antigens are collectively called H
antigens.
Other significant bacterial antigens include the porins, the heat-
shock proteins, and the exotoxins. The porins are proteins that form

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