Polymeric IgA is complexed with secretory component (SC) on the surface of human intestinal epithelial cells.

Viable suspensions of columnar cells were obtained from the surface and outer crypt epithelium of human colon mucosa by a combined treatment with citrate and EDTA solutions and mechanical disruption, but without the use of enzymes. A substantial fraction of the isolated cells contained free SC and secretory IgA in a cytoplasmic distribution that corresponded to previously reported immunohistochemical and immunoelectron-microscopical results obtained with tissue sections. On their surface the same cells were shown to bear SC complexed with J-chain-containing polymeric IgA, whereas only occasional traces of free SC were found. IgM was detected in the surface patches which contained the largest concentrations of SC and IgA. These findings demonstrate that in SC-producing epithelial cells SC molecules become exposed on the plasma membrane, thereby being able to bind specifically J-chain-containing IgA and IgM present in the tissue fluid. Such adsorptive complexing is probably a prerequisite for the selective pinocytotic transport of these two Ig classes through glandular epithelium in man.