Kinetics of mammary and intestinal IgA-producing cells in the lactating rat.

IgA-producing B lymphocytes in the lactating mouse mammary gland are thought to be derived from lymphoid tissues associated with the small intestine. By contrast, adoptive transfer studies in the rat have failed to confirm a simple entero-mammary migration of IgA plasma cell precursors during lactation. To explain this discrepancy we postulated that recent cIgA+ cell immigrants undergo extensive local proliferation in the rat mammary gland. The present study tested this hypothesis by determining mitotic indices of cIgA+ cells in the gland during lactation. The results did not support this contention and suggest that rat mammary cIgA+ B cells are not derived from the same pool of precursors providing IgA-producing B cells for the small intestine.