Differentiation of human lambda I variable regions with a monoclonal antibody to a defined, germ-line-encoded idiotope correlates with V lambda Ia chemical structure.

This article describes the characterization of a mouse monoclonal anti-idiotypic antibody (1H7B) prepared against a human monoclonal rheumatoid factor (RFSJ2) whose L chain utilized a V lambda I subgroup gene. The mAb 1H7B reacted with 6 of the tested 12 human V lambda I proteins, as well as with a newly produced lambda mAb whose V lambda gene usage has not as yet been determined. Because six of the 1H7B-positive mAb were heterogeneous with respect to both their VH gene utilization and antigenic specificity, and because mAb 1H7B did not react with any of the tested 43 kappa or 12 lambda proteins belonging to various subgroups other than V lambda I, mAb 1H7B appeared to be a V lambda I subgroup-specific reagent. The L chain specificity of mAb 1H7B was confirmed by Western blotting, and the inhibition of RFSJ2 binding to human Fc gamma by 1H7B provided additional evidence for the V region specificity of mAb 1H7B. The 11 sequenced V lambda I proteins used in this study were assigned to sub-subgroups by comparison with the previously published germ-line V lambda Ia, V lambda Ib, and V lambda Ic sequences. The mAb 1H7B only appeared to recognize V lambda Ia proteins as it reacted with five of the seven V lambda Ia, but not with three V lambda Ib or with one V lambda Ic protein. Because mAb 1H7B reacted with at least one V lambda Ia sequence in germ-line configuration, it appeared to be a marker for V lambda Ia sub-subgroup germ-line gene(s). The idiotope recognized by 1H7B was localized to the first framework region by inhibiting its binding to RFSJ2 with a synthetic peptide to the 11-24 amino acid region of V lambda Ia L chains. Comparison of the V lambda 1-24 region sequence of RFSJ2 with those of the two 1H7B-negative V lambda Ia mAb revealed a single amino acid difference at position 17, suggesting that the idiotope recognized by 1H7B encompassed this position.