Page 339 - Veterinary Immunology, 10th Edition

these mammals, the PPs do not develop until 2 to 4 weeks after
VetBooks.ir birth and persist into old age. The development of the PPs in some

group II animals appears to depend entirely on stimulation by the
normal intestinal microbiota, since they remain small and poorly

developed in germ-free animals.

Function

The ileal PPs of some group I species such as sheep function in a
manner similar to the avian bursa. Thus, ileal PPs are sites of rapid
B cell proliferation, although most cells then undergo apoptosis,

and the survivors are released into the circulation. If their ileal PPs
are surgically removed, lambs become B cell deficient and fail to
produce antibodies. The bone marrow of lambs contains many

fewer lymphocytes than the bone marrow of laboratory rodents,
and the ileal PPs are therefore their most significant source of B
cells.

Lymphoglandular Complexes

Lymphoglandular complexes are present in the wall of the large
intestine and cecum in horses, ruminants, dogs, and pigs. They
consist of submucosal masses of lymphoid tissue penetrated by

radially branching extensions of mucosal glands. These glands
penetrate both the submucosa and the lymphoid nodule. They are
lined by intestinal columnar epithelium containing goblet cells,
intraepithelial lymphocytes, and M cells (Chapter 22). Their
function is unknown, but they contain many plasma cells,

suggesting that they are sites of antibody production.

Bone Marrow

The specialized ileal PP is the primary lymphoid organ for B cells

only in group I mammals such as ruminants. In group II mammals
the bone marrow probably serves this function. There is no
exclusive B cell development site in the bone marrow, although it is
suggested that precursor B cells develop at the outer edge of the
marrow and migrate to the center as they mature and multiply.

Negative selection occurs within the bone marrow so that, as in

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