IMMUNOGENICITY OF 2 IDIOTOPES WITH A DIFFERENT IMMUNOGLOBULIN-CHAIN DISTRIBUTION EXPRESSED ON THE SAME ANTI-CD4-MAB

We have analyzed Ig chain location and immunogenicity of two distinct and spatially distant idiotopes (ids) expressed on the mouse anti- hum an CD4 mAb HP2/6 (Ab1). Western blot experiments indicated that id 14 (defined by the anti-idiotypic mAb F16-14D6) is conformational, as the association of the two HP2/6-chains is required for its full expressi on. id 23 (defined by the anti-idiotypic mAb F11-2302) is likely to be ''sequence dependent'', since it is also expressed on SDS- and reduci ng reagent-treated separated heavy and, to a lower extent, light chain s of HP2/6. Both ids were not detected, even as ''hidden idiotopes'', on a panel of anti-CD4 mAbs or polyclonal mouse Ig Abs. Functional stu dies suggested that id 23 displayed a markedly lower immunogenicity th an 14, as determined by the ability of sera from serial bleedings from 2 BALB/c mice immunized with mAb HP2/6 to inhibit the binding of mAb F11-2302 and F1614D6, respectively, to HP2/6. The results suggest that differences in the Ig-chains distribution of ids may markedly influen ce their immunogenicity, and that id 23 does not appear to behave as a regulatory id, because it is private and less immunogenic than the co nformational id 14. Thus, our data reinforce previous evidence that id 23 has none of the regulatory properties explored and, in contrast to previous findings, the simultaneous expression of an id on separated SDS- and reducing reagent-treated heavy and light chains of an antibod y molecule could not be related to its regulatory role.