Abstract
The ultrastructural localization of α heavy and κ light chains of immunoglobulin within lymphoblastoid cells of a human long term culture line, RPMI 4666, was studied by a combination of electron microscopy and immunocytochemistry. When cells were treated with peroxidase-conjugated antibodies that were monospecific for α chain or κ chain, and they were revealed cytochemically, the ultrastructural site of immunoglobulin accumulation was demonstrated as conspicuous electrondense precipitates within the cytoplasm of about 30% of the total cells.
In positive cells the κ chain was localized to the ergastoplasm, its membrane, the external layer of the nuclear membrane, and above all to ribosomes lining the ergastoplasmic membrane and the vicinity of the nuclear envelope.
On the other hand, the dominant site of α chain accumulation was in clusters of cytoplasmic polysomes, although α chain was also detected on the external layer of the nuclear envelope and on ribosomes associated with the ergastoplasmic membrane and nuclear envelope. Generalized staining of the cytoplasm suggesting diffusion of synthesized immunoglobulin to the cell surface, as reported with antibody-forming lymphoblasts in hyperimmunized animals, was never demonstrated in the present system.
The differential distribution of heavy and light chains suggests that they are formed separately at different sites and subsequently combined to each complementary chain prior to secretion even in lymphoblastoid cells.
