Syngeneic antiidiotypic monoclonal antibodies to the murine anti-HLA-DR,DP monoclonal antibody CR11-462

Two out of 625 hybridomas constructed with splenocytes from a Balblc mouse immunized with the murine anti-HLA-DR, DP monoclonal antibody CR11-462 secrete antiidiotypic antibodies. Binding assays with a panel of 12 anti-HLA class I, 14 anti-HLA class II, and 9 anti-human melanoma-associated antigen MoAbs showed that the idiotopes recognized by MoAb F3-C25 and F3-B6 are not expressed by any of the tested antibodies, even those which inhibit the binding of MoAb CR11-462 to cultured B lymphoid cells. Crossblocking experiments showed that the two idiotypes are distinct and spatially distant. Both idiotopes require the association of heavy and light chain of MoAb CR11-462 for their expression. The idiotope recognized by MoAb F3-B6 is an idiotope, since it is located outside the antigen combining site of MoAb CR11-462. The idiotope recognized by MoAb F3-C25 is a γ idiotope, since it is antigen inhibitable but does not posses an internal image of the antigen. Interestingly the MoAb F3-C25 displays a differential inhibitory effect on the binding of MoAb CR11-462 to lymphoid cells that express different HLA phenotypes or share the HLA-DRw6 allospecificity. These results suggest that antiidiotypic antibodies may sharpen our ability to dissect the heterogeneity of HLA class II antigens.