Signaling to a B-cell clone by Ek, but not Ak, does not reflect alteration of Ak genes.

The mouse B-cell clone, CH12.LX (Iak, Ly-1+, mu+, delta+), can be induced to differentiate and secrete antibody in an antigen-specific, H-2-restricted manner. Induction requires two signals. One must be provided by the binding of specific antigen to the membrane IgM; the other is delivered by the binding of Ek-specific T-cell hybridomas to the Ek molecules of CH12.LX (Bishop and Haughton 1986). Previous studies demonstrated that Ek-specific monoclonal antibodies (mAbs) could substitute for T cells in delivering the second differentiative signal (Bishop and Haughton 1986). Although CH12.LX cells present Ak to Ak-restricted or alloreactive T-helper cells, neither T cells nor mAbs specific for Ak induce differentiation (Bishop and Haughton 1986). However, since the Akspecific mAbs tested previously were beta-chain-specific and the Ia epitope specificity of the T cells used was unknown, it is possible that the differentiative signal delivered to the CH12.LX class II molecule is chain-specific. Here we report the effects of ten additional Iak-specific mAbs upon the differentiation of CH12.LX. In addition, a cDNA library was prepared from CH12.LX cells, clones corresponding to the alpha and beta chains of the Ak molecule were isolated, and their nucleotide sequences were determined. Finally, the Ak and Ek molecules of CH12.LX and H-2k spleen cells were compared by two-dimensional gel electrophoresis to examine possible post-translational differences in the Iak molecules of CH12.LX.