Ontogeny of secretory component in rat liver.

The ontogeny of the expression of secretory component (SC), the receptor for transepithelial transport of polymeric immunoglobulins, in the rat liver was assessed by measuring the SC concentration in liver homogenates of rats killed from birth to 60 days of age, and by quantifying the daily SC secretion of in vitro cultured hepatocytes isolated from rats similarly killed from 2 days before birth to 60 days of age. With both methodologies, only very small amounts of SC were produced by the rat liver up to 20 days of age, whereafter expression of SC markedly increased. The development of SC production in the rat liver was co-ordinate with that previously reported in the rat small intestine, preceding the appearance of large numbers of intestinal IgA plasmacytes. These data further emphasize the importance of the liver contribution, via the bile, to the intestinal secretory IgA system of the rat.