Presence of J chain in human immunocytes containing various immunoglobulin classes

Abstract

THE polypeptide J chain is common to dimeric IgA and polymeric IgM1–3. Immunocytes producing such immunoglobulins have been shown to synthesise J chain4–6; its incorporation has therefore been assumed to be an essential step in the intracellular joining of the monomer (H2L2) subunits. But the finding of a monoclonal polymeric IgM lacking J chain7,8, and reassociation of IgM subunits depleted of J chain9, have led to questioning of its role as an initiator of polymerisation. Experiments demonstrating J chain in four murine IgG myeloma cell lines10 prompted me to examine its cellular localisation in human biopsy material. Cytoplasmic J chain was detected in IgD, IgM, IgG, and IgA immunocytes by direct immunofluorescence. This localisation was compared with the cytoplasmic ability to bind “secretory component” (SC) in vitro in a SC-affinity test that has been postulated to distinguish between polymer and monomer producing cells11.