Secretory component-dependent binding of immunoglobulin A in the rat, monkey and human: a comparison of intestine and liver.

The source and significance of immunoglobulin A in bile remains controversial. In the rat, and several other species, immunoglobulin A is transported through hepatocytes by a specific receptor, secretory component. In humans, immunohistochemical methods have indicated a distinct lack of receptors for immunoglobulin A on hepatocytes. Binding assays with 125I-immunoglobulin A and membranes from hepatocytes and intestinal cells of the rat display secretory component-dependent binding. Primate intestinal cells also show secretory component-specific binding of immunoglobulin A. Primate liver, on the other hand, does not show immunoglobulin A binding mediated by the polymeric immunoglobulin receptor.