The class of immunoglobulin M (IgM) characterized by high molecular weight proteins with a sedimentation coefficient of 19S, includes a smaller molecular form with an S(20,[unk]) of approximately 7. The synthetic origin of the 7S IgM was investigated by biosynthetic studies on bone marrow cells from three patients with macroglobulinemia whose sera contained 7S IgM and 19S IgM. Labeled 7S IgM and 19S IgM were identified in extracellular culture fluids by radioimmunochemical techniques. The separation of the two molecular forms of IgM by density-gradient ultracentrifugation of the culture fluids before radioimmunochemical analyses permitted the identification of both the labeled 7S IgM and 19S IgM. One patient's serum contained two separate and distinct 19S IgM proteins as well as 7S IgM. The use of specific isolated carrier IgM proteins permitted the radioimmunochemical detection of labeled 7S IgM and both 19S IgM proteins. The introduction of cycloheximide into a culture system effects the cessation of protein synthesis. The analyses of culture fluids harvested at timed intervals after the addition of cycloheximide revealed not only the stability of 19S IgM to intracellular proteolysis, but also provided evidence for a possible precursor-product relationship between the 7S IgM and the 19S IgM. The demonstration that the labeled 7S IgM is neither an in vitro breakdown product of 19S IgM nor a resultant of 19S IgM intracellular catabolism substantiated the synthetic origin of 7S IgM in human sera.

Bone Marrow↗

PubMed1969

Bence Jones proteins and light chains of immunoglobulins. II. Immunochemical differentiation and classification of kappa-chains.

Three distinct classes of kappa light polypeptide chains have been detected immunochemically by an antiserum (R185) prepared against a kappa Bence Jones protein with a glutamyl amino terminal residue. This antiserum had specificity for kappa light chains with glutamyl amino terminal residues and differentiated kappa-chains with aspartyl amino terminal residues into two classes: the three kappa-chain classes have been designated as kappa(glu), kappa(aspII), and kappa(aspI). The ability of antiserum R185 to detect these antigenic differences on the intact immunoglobulin molecule, as well as on the isolated light chain or Bence Jones protein, made feasible the direct classification of type K myeloma proteins and M-macroglobulins (Waldenström). The multispecificity of the antiserum permitted the quantitation of type kappa(glu) light chains in normal, hypergammaglobulinemic, and hypogammaglobulinemic sera. Whereas the distribution of myeloma proteins and Bence Jones proteins in the kappa(glu) class correlated with the distribution of kappa(glu) chains in normal and hypergammaglobulinemic sera, the M-macroglobulins in the kappa(glu) class represented 90% of the total M-macroglobulins tested and revealed a marked divergence from the range of 24-31% of kappa(glu) immunoglobulins in normal sera. A preponderance of kappa(glu) chains was detected in the sera from patients with non-sex-linked hypogammaglobulinemia and represented 60-77% of the total type K light chain content. The controlled cleavage of a Bence Jones protein representative of each kappa-chain class into its variant half and constant half made possible the localization on the light polypeptide chain, the reactive sites for which antiserum R185 had specificity. The correlations between immunochemical and structural classification of kappa light chains are discussed.

Bence Jones Protein↗

PubMed1969