Three distinct classes of κ light polypeptide chains have been detected immunochemically by an antiserum (R185) prepared against a κ Bence Jones protein with a glutamyl amino terminal residue. This antiserum had specificity for κ light chains with glutamyl amino terminal residues and differentiated κ-chains with aspartyl amino terminal residues into two classes: the three κ-chain classes have been designated as κglu, κaspII, and κaspI.

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 κglu light chains in normal, hypergammaglobulinemic, and hypogammaglobulinemic sera. Whereas the distribution of myeloma proteins and Bence Jones proteins in the κglu class correlated with the distribution of κglu chains in normal and hypergammaglobulinemic sera, the M-macroglobulins in the κglu class represented 90% of the total M-macroglobulins tested and revealed a marked divergence from the range of 24–31% of κglu immunoglobulins in normal sera. A preponderance of κglu 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 κ-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 κ light chains are discussed.

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