Immunoglobulin production and secretion by variant clones of the MOPC 315 mouse myeloma cell line.

A clone of the IgA-producing MOPC 316 myeloma cell line (clone 25) was used to isolate three populatjons of variant cultures: λ-chain producing and secreting cells (clone 26); λ-chain producing but not secreting cells (clone 37); and non-Ig producing cells (clone 36). The inability of clone 37 to secrete the λ-chains that it produced provided an opportunity to ascertain whether a structural defect in the λ-chains or an aberration in the secretory apparatus of the cell was responsible for absence of secretion. The results obtained were compared with the λ-chain producing and secreting clone 26 cells, while the nonproducing clone 36 cells served as a negative control. It was found by in vivo labeling studies that secreting clone 26 cells produced approximately the same amount of λ-chains as did nonsecreting clone 37 cells. The λ-chains turned over somewhat more rapidly (2 as opposed to 3 hr) in clone 26 cells, but in both cases the λ-chains were localized to them icrosomal fraction of the cell. The presence in nonsecreting clone 37 cells of a markedly dilated rough surfaced endoplasmic reticulum, presumably filled with λ-chains, as determined by transmission electronmicroscopy, was the morphologic counterpart of absence of secretion in these cells. Poly Acontaining RNA prepared from clone 26 and 37 cells both programmed cell-free translation systems prepared from wheat embryo extracts and reticulocyte lysates to produce a λ-chain precursor. Mature λ-chains were produced by these RNA in Xenopus Iaevis oocytes and compartmentalization studies showed that they localized equally well to the microsomal fraction of the oocytes. Poly A-containing RNA from clone 36 did not program the synthesis of any Ig chains. λ-Chains could be demonstrated by the hydrogen peroxide catalyzed lactoperoxidase iodination reaction on the surface of both secreting clone 26 and nonsecreting clone 37 cells. The λ-chains produced by clone 26 cells differed from clone3 7 cells by focusing differently in a pH gradient. These studies showed that both secreting clone 26 and nonsecreting clone 37 cells synthesized and processed λ-chains in a similar fashion but secretion was not observed with clone 37 cells because of a structural alteration in th λ-echains.