The synthesis and assembly of immunoglobulins by malignant human plasmacytes. III. Heterogeneity in IgA polymer assembly

The pathways of immunoglobulin synthesis and assembly have been studied in bone marrow cells obtained from 9 patients whose serum contained substantial amounts of homogeneous IgA1 myeloma proteins. Eight of the 9 cell samples synthesized light chains in excess of heavy chains. A variety of assembly intermediates, including αL, α 2 and α 2 L, were also noted. The major intracellular molecule in most cases was α 2 L 2 although larger polymers were noted in the secretions and serum of most of the patients. In only one instance was a large amount of polymer larger than α 2 L 2 found inside the cell. As is the case for the assembly for IgM, the sites of IgA polymer assembly and factors responsible for the observed heterogeneity have not yet been established.