Signaling to a B-cell clone by E^k, but not A^k, does not reflect alteration of A^k genes

The mouse B-cell clone, CH12.LX (Ia^k, Ly-1⁺, μ⁺, δ⁺), 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 E^k-specific T-cell hybridomas to the E^k molecules of CH12.LX (Bishop and Haughton 1986). Previous studies demonstrated that E^k-specific monoclonal antibodies (mAbs) could substitute for T cells in delivering the second differentiative signal (Bishop and Haughton 1986). Although CH12.LX cells present A^k to A^k-restricted or alloreactive T-helper cells, neither T cells nor mAbs specific for A^k induce differentiation (Bishop and Haughton 1986). However, since the A^kspecifc mAbs tested previously were β-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 11 molecule is chain-specific. Here we report the effects of ten additional Ia^k-specific mAbs upon the differentiation of CH12.LX. In addition, a cl)NA library was prepared from CHI 2.LX cells, clones corresponding to the α and β chains of the A^k molecule were isolated, and their nucleotide sequences were determined. Finally, the A^k and E^k molecules of CH12.LX and H-2^k spleen cells were compared by two-dimensional gel electrophoresis to examine possible post-translational differences in the Ia^k molecules of CH12.LX.