Composition of the lymphoid cell populations from omental milky spots during the immune response in C57BL/Ka mice

The lymphoid cell composition of milky spots was analyzed in unprimed mice before and after i.p. immunization with sheep red blood cells. Milky spots contained surface immunoglobulin‐positive B lymphocytes, and T cells of the helper and cytotoxic phenotype. After secondary antigen challenge (a) the number of lymphocytes increased up to 40‐fold, (b) B and T cells were found to segregate into distinct areas in situ, and (c) lymphocytes were found to associate with I‐A‐negative stromal cells in vivo. These findings qualify milky spots as a peripheral lymphoid organ exhibiting a remarkable change in number and composition of lymphocytes in response to a local antigen stimulus.