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Secretory component (SC) was found to be synthesized by isolated rat hepatocytes. SC was detected by radioimmunoassay and cultured hepatocytes were found to synthesize 0.078 microgram SC/10(6) hepatocytes in a 48-h period. SC was also present on the surface of hepatocytes as detected by the specific binding of radiolabeled anti-SC antibodies as well as by the detection of specific membrane staining in indirect immunofluorescence tests using specifically purified anti-SC antibodies. Rat SC was detected on hepatocytes and intestinal epithelial cells but not on peripheral blood lymphocytes, unfractionated spleen cells, or erythrocytes. Specific binding of radiolabeled rat dimeric IgA to rat hepatocytes was also observed and evidence was obtained to indicate that such binding was mediated by SC. Thus, prior incubation of hepatocytes with anti-SC prevented binding of radiolabeled IgA. Moreover, prior incubation of radiolabeled IgA with rat SC prevented binding of the IgA to isolated hepatocytes. Cells treated with 0.25% trypsin lost their ability to bind to radiolabeled dimeric IgA.
Socken et al. (Sat,) studied this question.