Immunoglobulin lambda light chain evolution: Igl and Igl-like sequences form three major groups

The nucleotide sequences, and the derived protein sequences, of immunoglobulin (Ig) Igl, Igl-like VpreB genes and the protein sequences of Igl-C regions were aligned and compared. A classification of the Igl and Igl-like VpreB sequences into three categories, designated groups I, II, and III, is proposed. Group I contains the human and mouse Igl-like VpreB genes. Group II contains Igl-V genes of the rabbit and the recently described mouse Igl-Vx gene. Group III includes the Igl-V genes, encoding all other known Igl-V region protein sequences, of mouse, rat, human, pig, sheep, and chicken. An evolutionary analysis of the three groups is presented, and suggests that the group III genes are evolving at a faster rate than those of the other groups and that within this group a further subdivision is possible: the V lambda-encoding genes of mouse, rat, and one human subgroup evolve faster than other group III genes. It is suggested that all mammalian species contain Igl-V genes of each group. A similar comparison between the protein sequences encoded by the known Igl-C genes indicates that the duplication of the Igl-J-C gene pairs occurred independently in each species, after mammalian speciation, and that the Igl-V-(J-C)(J-C) gene clusters of the mouse may not have their homologues in other species.