Page 706 - Veterinary Immunology, 10th Edition

enters M cells is not degraded. It may be presented directly to
VetBooks.ir permitted to pass along the intercellular space to the tissue fluid.
intraepithelial lymphocytes within the M cell or, alternatively,

From here, it will be carried to the draining lymph nodes.

Artiodactyls possess gut-associated lymphoid tissues that
develop at the extreme end of the ileum during fetal life. They
contain ~90% B cells with very few T cells and involute within

weeks after birth. A similar lymphoid organ called the sacculus
rotundus develops in rabbits. It was long believed that these
lymphoid organs in the lower hind gut are the primary lymphoid

organs where B cells develop. However, recent studies on piglets
have cast doubt on this. Removal of the piglet ileal Peyer's patch
does not result in a B cell deficiency such as would occur in a
bursectomized bird. There are no differences in B cell diversity,
distribution, or repertoire in piglets where this organ has been

removed. In addition, there is no evidence that B cell diversification
occurs within this organ. Evidence now suggests that in pigs at
least, the ileal Peyer's patch is a secondary mucosal lymphoid organ

that regulates the initial microbial colonization of the lower bowel.
There may be no discrete organ equivalent to the bursa in these
mammals.
Many dietary components have a profound effect on the
organization and maintenance of intestinal immune tissues. For

example, vitamin A metabolites play a role in the differentiation
and functioning of B and T cell subsets. Likewise, dietary vitamin D
alters B and Th responses, inhibiting Th1 and enhancing Th2

activity. Dietary lipids influence prostaglandin and leukotriene
synthesis and so modify inflammatory responses. Collectively,
these and other dietary components play a key role in ensuring that
the intestinal lymphoid tissues function optimally.

Effector Sites

Although Peyer's patches are full of lymphocytes, most IgA is
produced in diffuse lymphoid nodules and in isolated plasma cells

scattered throughout the walls of the intestine, in bronchi, in
salivary glands, and in the gallbladder.

B Cells

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