Page 707 - Veterinary Immunology, 10th Edition

B cells respond to antigen that penetrates the enterocyte barrier.
VetBooks.ir Some of these responding B cells migrate to regional lymph nodes

and into intestinal lymphatics, from which they reach the thoracic
duct and enter the bloodstream. These circulating IgA-positive B

cells have an affinity for all body surfaces. As a result, they colonize
not only in the intestinal tract but also at the respiratory tract,
urogenital tract, and mammary gland. Thus antigen priming at one
location will permit antibodies to be synthesized and secondary

responses to occur at locations remote from the priming site,
reflecting the existence of a common mucosal immune system (Fig.
22.9). The movement of IgA-positive B cells from the intestine to the
mammary gland is especially important since it provides a route by

which antibodies directed against intestinal pathogens can be
transferred to the newborn through milk. Oral administration of
antigen to a pregnant animal will thus result in the appearance of
IgA antibodies in its milk. In this way, antibodies directed against

intestinal pathogens will flood the intestine of the newborn animal.
T cells originating within the Peyer's patches will also home
specifically to the intestinal mucosa by using specialized vascular
adhesive molecules. For example, mucosal addressin cell-adhesion

molecule-1 (MAdCAM-1) is an adhesion molecule expressed on the
high endothelial venules of Peyer's patches and on venules in
intestinal lamina propria and the mammary gland. Its ligand is the
lymphocyte integrin α4/β7. B and T cells that express this integrin

migrate preferentially to the intestine and the mammary gland.

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