Nucleolus-associated localization of J chains in IgG 1(lambda)-producing myeloma cells.

By using both direct and indirect immunofluorescence technics and the PAP method, the authors observed an unusual immunocytochemical staining pattern in myeloma cells producing IgG 1(lambda). J chains were localized mainly as intranuclear spots, compared with gamma and lambda chains that are diffusely distributed in the cytoplasm with dense perinuclear accumulation. The present findings on the location, size, and number of the intranuclear spots suggest that J chains are nucleolus associated. The authors hypothesize that J chains are synthesized in the cytoplasm and transported into the nucleolus, where they associate with nucleolar proteins, or that they are synthesized within the nucleolus, which participates in biogenesis of ribosomes.