Immunoglobulin biosynthesis. I. A myeloma variant secreting light chain only

Cell cycle kinetics of the accumulation of heavy and light chain immunoglobulin proteins in a mouse hybridoma cell line

Rates of accumulation of immunoglobulin proteins have been determined using flow cytometry and population balance equations for exponentially growing murine hybridoma cells in the individual G1, S and G2+M cell cycle phases. A producer cell line that secretes monoclonal antibodies, and a nonproducer clone that synthesizes only kappa-light chains were analyzed. The pattern for the kinetics of total intracellular antibody accumulation during the cell cycle is very similar to the previously described pattern for total protein accumulation (Kromenaker & Srienc 1991). The relative mean rate of heavy chain accumulation during the S phase was approximately half the relative mean rate of light chain accumulation during this cell cycle phase. This indicates an unbalanced synthesis of heavy and light chains that becomes most pronounced during this cell cycle phase. The nonproducer cells have on average an intracellular light chain content that is 42% lower than that of the producer cells. The nonproducer cells in the G1 phase with low light chain content did not have a significantly higher rate of light chain accumulation relative to other G1 phase nonproducer cells. This is in sharp contrast to what was observed for the G1 phase producer cells. In addition, although the relative mean rate of accumulation of light chain was negative for G2+M phase nonproducer cells, the magnitude of this relative mean rate was less than half that observed for the producer cells in this cell cycle phase. This suggests that the mechanisms that regulate the transport of fully assembled antibody molecules through the secretion pathway differ from those which regulate the secretion of free light chains. The results reported here indicate that there is a distinct pattern for the cell cycle dynamics of antibody synthesis and secretion in hybridomas. These results are consistent with a model for the dynamics of secretion which suggests that the rate of accumulation of secreted proteins will be greatest for newborn cells due to an interruption of the secretion pathway during mitosis.

The current status of multiple sclerosis intra-blood-brain-barrier IgG synthesis

The status of the central nervous system as an immunologic organ synthesizing IgG in several neurological diseases has been established convincingly in the past two decades. The measurement of intra-BBB IgG synthesis has been accomplished. It has been demonstrated that this synthesis is a potential marker for an abnormal immunologic process within the CNS which if manipulated may be a quantifiable aspect of disease modulation. Modulation of intra-BBB IgG synthesis is feasible, but there is no evidence yet that modulation of this synthesis is an index of effective disease control in MS. Only ACTH and corticosteroids lead to a significant and lasting depression of intra-BBB IgG synthesis, even though clonal eradication is not achieved. Based on our immunopharmacologic studies in MS we have proposed an immunokinetic model. The qualitative analysis of the specificity of IgG synthesized intra-BBB in MS has not led to the etiology of MS, but utilization of quantitative methods may. Questions raised by this review with suggested experiments to advance further our understanding of intra-BBB IgG synthesis as it relates to the etiopathogenesis of MS are included.

Appearance of a variant of MOPC 104E which does not react with dextran B-1355s

MOPC 104E is a mouse plasmacytoma which produces an IgM (lambda) myeloma protein. This IgM protein has a binding specificity for dextran B-135s. This report describes a variant of the MOPC 104E tumor which secretes a myeloma protein which does not react with the dextran. The apparent variant of MOPC 104E arose spontaneously during routine passage of the MOPC 104E tumors in Balb/C mice and appears to be stable.

Cell-free translation of immunoglobulin messenger RNA from MOPC-315 plasmacytoma and MOPC-315 NR, a variant synthesizing only light chain

Total poly(A)-containing mRNA was isolated from the MOPC-315 and MOPC-315 NR plasmacytomas. The RNA was further fractionated on sodium dodecyl sulfate-sucrose gradients. The MOPC-315 mRNA fractions directed the synthesis of both the heavy chain and light chain precursor of the MOPC-315 IgA protein in a cell-free extract of Ehrlich ascites tumor cells. None of the MOPC-315 NR mRNA fractions tested programmed the synthesis of the heavy chain in this system. Analysis of cell-free products by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and by immunoprecipitation demonstrated that no translatable heavy chain mRNA could be extracted from the MOPC-315 NR variant plasmacytoma.

Mutations in immunoglobulin-producing mouse myeloma cells

Three mouse myeloma cell lines were cloned in soft agar and screened by an antiserum overlay method for variants defective in secretion of the myeloma protein. Variants that had lost the capacity to synthesize heavy chains arose spontaneously at a high rate of about 10(-3) per cell per generation. Such variants lost the capacity to produce light chains at a similarly high rate. After cells were treated with the acridine half mustard ICR-191, variants occurred with an even higher incidence, and some of these synthesized heavy chains differing from that of the parent.

Differentiation of mouse plasmocytomas in vitro: two phenotypically stabilized variants of the same cell

Mouse myelomas from Balb/c and C3H mice were established in tissue culture for more than 200 passages. When allowed to attach to a surface, they differentiated into two stabilized forms, one of which was fibroblast-shaped, grew without contact inhibition, and could be transplanted back to mice. The other had the morphology of epithelial cells, showed contact inhibition, and was not transplantable back to mice. For one strain (MOPC 173) it was demonstrated that both types of cells synthesize molecules with idiotypic determinants of the original myeloma protein. The relationship between the host cells and a leukemia-type virus present in the original tumor cells has been studied during different stages of cellular differentiation.

Leukemia viruses associated with mouse myeloma cells

Myeloma cells derived from BALB/c and C3H mice show evidence of infection by a murine leumemia virus. The immunoglobulin-producing myelomas secrete an RNA-containing virus with a density of 1.20 to 1.22 gm/cm(3). RNA with a sedimentation coefficient of 74 S in 0.1 M sodium sodium chloride has been isolated from secreted virus particles and has a base composition similar to that found for other murine leukemia virus RNA. An intracellular virus particle has been partially purified and has a density of 1.29 to 1.32 gm/cm(3). Both extracellular and intracellular virus particles contain the leukemia virus group-specific antigen.

Synthesis, assembly, and secretion of gamma globulin by mouse myeloma cells. I. Adaptation of the Merwin plasma cell tumor-11 to culture, cloning, and characterization of gamma globulin subunits

MPC-11 myeloma tumor cells were adapted to growth in continuous culture. The cultured cells resembled the parent tumor in that they produced the fully assembled gamma globulin molecules as well as six unassembled molecules. Although cultured and tumor cells synthesized excess light chains, the molar ratio of light (L) to heavy (H) chains was approximately 1.7:1 in the culture, and 3.5:1 in the tumor. The cultured cells also produced fewer half molecules and free light chains than the parent tumor. Peptide column analysis did not reveal differences in the primary structure of the H chains derived from the parent tumor and the culture. The L chains may have differed by a minor peptide. As much as 20% of the newly labeled cytoplasmic proteins and almost 100% of the proteins secreted by the cultured myeloma cells could be precipitated by specific antiserum. The immune precipitates contained seven different gamma globulin molecules, six of which were characterized according to their molecular size and H and L chain content as fully assembled molecules (H(2)L(2)), heavy chain dimers (H(2)), half molecules (HL), H, light chain dimers (L(2)), and L chains. All gamma globulin subunits as well as the complete H(2)L(2) molecule were produced and secreted by splenic clones of the parent MPC-11 tumor, and agar clones of the cultured cells. This indicates that the various gamma globulin subunits were produced by the same cell and did not reflect cellular heterogeneity with respect to gamma globulin synthesis.