Idiotypic analysis of anti-I-Ak monoclonal antibodies. I. Production and characterization of syngeneic anti-idiotypic mAb against an anti-I-Ak mAb.

To analyze the idiotype (Id) of anti-Ia antibodies elicited during alloimmune responses, we produced syngeneic mouse anti-Id monoclonal antibodies (mAb) reactive with the Id of the 11-5.2.1.9 (11-5) mouse anti-I-Ak (BALB/c anti-CKB) mAb. Two such anti-Id mAb, IA2 (IgG2a) and IIID1 (IgG1), detect structurally related idiotopes located within the binding site of 11-5 for I-Ak antigens. A third anti-Id mAb, VC6 (IgG1), detects an idiotope located either inside or outside of, but presumably proximal to, the 11-5 antigen-binding site, because its expression correlates with the antigenic specificity of 11-5. None of the idiotopes detectable by these three anti-Id mAb are accessible when the binding site of 11-5 is occupied by an I-Ak molecule. The association constants of these anti-Id mAb for their cognate Fab-linked Id range from 2 X 10(9) to 1 X 10(10) M-1. The three anti-Id-producing hybridomas were found with a frequency of 0.008% among growing hybrid colonies. Even though these anti-Id mAb detect public idiotopes (IdX) on 11-5, they do not detect the presence of such IdX markers in the sera of five syngeneic BALB/c mice hyperimmunized with C3H (I-Ak) spleen cells. This suggests that 11-5 represents a BALB/c idiotype infrequently expressed by serum immunoglobulins. The 11-5 idiotopes detectable by IA2, IIID1, and VC6 seem to be conformationally determined by the interaction of 11-5 H and L chains and are not confined to one or the other of these subunit polypeptides. Thus, the expression of the 11-5 Id may be regulated by both VH and VL genes.