Identification of secretory component as an IgA receptor on rat hepatocytes.

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Abstract
Secretory component (SC) was synthesized by isolated rat hepatocytes. SC was detected by radioimmunoassay and cultured hepatocytes synthesized 0.078 .mu.g SC/106 hepatocytes in a 48 h period. SC was also present on the surface of hepatocytes as detected by specific binding of radiolabeled anti-SC antibodies as well as by 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 Ig[immunoglobulin]A to rat hepatocytes was also observed and evidence was obtained to indicate that such binding was mediated by SC. Prior incubation of hepatocytes with anti-SC prevented binding of radiolabeled IgA, and 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.