Haplotype-specific differences in signaling by transfected class II molecules to a Ly-1⁺ B-cell clone

CH12.LX B cells are responsive to antigen-dependent differentiative signals transmitted through their surface E(k) molecules. Although CH12.LX cells express surface A(k) molecules with normal protein sequence, the A(k) molecules do not deliver differentiative signals to these B cells. To determine whether introduction of a new A molecule into CH12.LX cells would correct this deficiency, CH12.LX cells were transfected with the genes encoding new a(α) and/or A(β) molecules. It was found that transfected cells responded to antigen-specific signals delivered via the E(α)(k)E(β)(k), A(α)^bA(β)^b, or A(α)(k)A(β)^b molecule. However, the B cells did not respond to signals generated by the molecule A(α)(k)A(β)(k), A(α)^bA(β)(k), A(α)(k)A(β)(d), or A(α)(k)A(β)(u). Comparison of these sequences suggests that two A(β) residues, His-47 and Trp-197, are important to the transmission of differentiative signals to B cells.