The specificity of chain interactions among immunoglobulins. Combinations of gamma chains with kappa chains of the same subgroup as in the parent immunoglobulin G.

1. The specificity of combination of heavy and light chains from selected human immunoglobulins was examined in the light of greater structural information than in previous studies. Heavy (gamma) chains from immunoglobulin G (kappa) myeloma proteins were allowed to combine with their homologous light (kappa) chains or with other kappa chains of the same variable-region subgroup. The affinity of each such pairing was assessed by having the test kappa chain compete with a standard population of normal light chains. 2. There was a spread of affinities among the heavy-light pairings with the homologous pairings having an average affinity significantly higher than the heterologous pairings. 3. It follows that (a) the preference shown for homologous heavy-light pairings is not explicable simply in terms of the known subdivisions of the variable and constant regions of the chains, and (b) it is unlikely that those residues specifying the subgroups of kappa-chain variable regions have a predominant role in the formation of interchain bonds with the gamma-chain variable regions.