Studies on J chain and binding site for secretory component in circulating human B cells.

Lymphocyte-enriched mononuclear cell fractions were obtained from the peripheral blood of four healthy young adults. Living B cells with membrane immunoglobulin (Ig) were studied by immunofluorescence to reveal exposed J-chain determinants or surface affinity for the secretory component (SC). Alcohol-fixed cell smears were similarly studied with and without prior denaturation in acid urea. It was concluded that J chain-containing polymeric Ig of endogenous origin is generally not present on the surface of circulating B cells. If occasional cells bear IgM or IgA polymers rather than monomers, their SC-binding site must be concealed to a degree that it is not functional. Affinity for SC is therefore unlikely to be involved in a selective homing of IgM- and IgA-immunocyte precursors from peripheral blood to glandular regions.