N-terminal analysis of normal immunoglobulin light chains. I. A study of thirteen individual humans

Most kappa immunoglobulin mRNA in human lymphocytes is homologous to a small family of germ-line V genes

The mammalian immune system produces 10(6)-10(8) different antibody-combining sites. It has been established that three factors contribute to the diversity of immunoglobulin variable regions: multiple gene segments in the germ line, somatic recombination of these segments and somatic mutation. However, the relative importance of these components in generating the antibody repertoire is unknown. One way to assess the importance of the germ-line component relative to the somatic components would be to determine the number of germ-line V genes expressed. Here, I report that a family of about 25 human germ-line V genes encodes over 50% of kappa mRNA in spleen or peripheral blood lymphocytes. This observation agrees with gene-counting experiments which indicated that the total number of V kappa genes in the human genome is quite small, about 50 or less. Such a small number of germ-line V kappa sequences implies that somatic mutation is the major source of human kappa-chain diversity.

Light chain sequences of human IgM cold agglutinins (variable-region subgroups amino-acid sequence-kappa light chain-N-terminal)

The amino-terminal amino-acid sequence has been determined for the kappa light chains of nine IgM cold agglutinins with specificity for blood group-related carbohydrate antigens. Six of the nine sequences corresponded to the prototype VK(III) subgroup pattern, two to that of subgroup VK(II), and only one to the VK(I) subgroup. This distribution of kappa subgroups differs markedly from that of normal and myeloma proteins sequenced to date, where the VK(I) subgroup is more prevalent than either VK(II) or VK(III). Evidence is presented that supports the conclusion that the unusual subgroup distribution relates to the antibody property itself and not to some other attribute of these molecules.

Heavy-chain variable regions in normal and pathological immunolobulins

Aminoacid sequence analysis of immunoglobulin G heavy chains from each of 15 normal individuals showed the presence of VHIII subgroup sequences in all individuals, to an extent of about 15-25% of the total. Therefore, different subgroups of the heavy-chain variable region are not products of alleles of a single gene.N-terminal aminoacid sequences were determined for ten heavy chains of myeloma proteins that belonged to the VHIII subgroup. Our results demonstrate the existence of a "hypervariable" region of sequence between positions 30 and 35, homologous to one of the three hypervariable regions of light chains. At several positions, variants of the basic sequence are repeated in different proteins. It is likely that such variants are derived from several recently evolved genes that constitute the VHIII subgroup.