Page 358 - Veterinary Immunology, 10th Edition

Other Secondary Lymphoid Organs
VetBooks.ir Secondary lymphoid organs include not only the spleen and lymph

nodes but also the bone marrow, tonsils, and lymphoid tissues

scattered throughout the body, most notably in the digestive,
respiratory, and urogenital tracts. The lymphoid tissues of the
intestinal tract constitute the largest pool of lymphocytes in the
body, but the bone marrow also contains very large numbers of

lymphocytes. If antigen is given intravenously, much will be
trapped not only in the liver and spleen but also in the bone
marrow. During a primary immune response, antibodies are mainly
produced in the spleen and lymph nodes (Fig. 12.20). Toward the

end of that response, memory cells leave the spleen and colonize
the bone marrow. When a second dose of an antigen is given, the
bone marrow produces very large quantities of antibody and is the
major source of antibodies in adult rodents. Up to 70% of the

antibody to some antigens may be produced by cells in the bone
marrow (Fig. 12.21). Fat-associated lymphoid clusters are small
secondary lymphoid nodules within adipose tissues underlying
serosal membranes such as the mesentery.

FIG. 12.20 Although the primary immune response to
intravenously injected antigen takes place in lymph nodes or
spleen, the antibodies produced in a secondary response are
largely produced in the bone marrow.

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