Secretory component in immmunoglobulin deficiency: and immunoelectron microscopic study of intestinal epithelium.

The ultrastructural sites of secretory component (SC) in the intestinal epithelium of severely immunoglobulin-deficient and immunologically intact persons were compared. SC was found in the same sites in the immunoglobulin-deficient and normal epithelium: perinuclear spaces, rough endoplasmic reticulum, Golgi complexes, external surfaces and endocytic invaginations of the basolateral plasmalemma, and in membranous vesicles throughout the cytoplasm. These observations suggest that the synthesis, external expression and transcellular migration of SC occur independent of the presence of immunoglobulins. The migration of SC from the basolateral cell surfaces to apical surfaces may be an inherent property of epithelial cells and the primary event in the translocation of polymeric immunoglobulins across the cells to external body fluids.