The development of immunoglobulin-containing cell populations in intestine, spleen and mesenteric lymphnode of the young rat.

Immunohistological and immunochemical techniques were used to study the absorption, synthesis and secretion of immunoglobulins A, G and M in rats from 0-51 days of age. Intestinal epithelial cell-staining with IgA and IgG occurred during the first two weeks of the suckling period. Immunoglobulin G was detected in serum at all ages studied. IgA was first detected in animals aged one week, the levels rising gradually in succeeding weeks; there was a concomitant increase in the number of IgA-containing cells in the lamina propria of the intestine. No evidence was obtained to indicate the route of intestinal secretion of this class of immunoglobulin. Immunoglobulin M-containing cells were present in only small numbers.