J chain biosynthesis in pre-B cells and other possible precursor B cells.

Abstract

Human cell lines that resemble precursors in the B cell lineage synthesize J (joining) chain. In vivo pulse labeling, together with in vitro translation of total cellular RNA in a wheat germ cell-free system, detected the synthesis of J chain in Ig-secreting cell lines, in a cell line with only surface IgM, and in the pre-B-like cell line Josh 4 and the round cell lines Josh 7 and KLM 2. The primary translation products of J chain from all these cell lines were indistinguishable from one another by serologic criteria, by relative mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, by charge as judged by alkaline-urea gel electrophoresis, and by peptide mapping. The onset of J chain biosynthesis apparently represents a relatively early event in B cell ontogeny, occurring before the development of Ig polymer-secreting cells. Its role may be fundamental to the biosynthesis of all immunoglobulins at different stages of B cell differentiation.