Page 716 - Veterinary Immunology, 10th Edition

bound, the IgA-antigen complexes will bind to pIgR and be actively
VetBooks.ir transported back across the enterocytes into the intestinal lumen.

IgA can therefore act at three different levels to exclude foreign
antigens: within the submucosa, within enterocytes, and within the

intestinal lumen.

FIG. 22.14 IgA is unique in that it can act in three locations. It can
bind antigen in tissue fluid or in enterocytes as well as in the
intestinal lumen. The bound antigen in tissues or enterocytes is
carried to the intestinal lumen.

Immunoglobulin M

The earliest immunoglobulins found in the intestine of the newborn
are of the IgM class. IgM will also bind to pIgR and is carried
through the enterocyte to the lumen. Because of its structure,
however, secretory IgM is much more susceptible to proteases than
secretory IgA.

Immune Elimination

Immunoglobulin E

Because IgA does not activate complement, it functions by immune
exclusion. There is a second line of defense, however, that destroys

antigen that penetrates the mucosal barrier (immune elimination).

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