Immunogenicity of two idiotypes 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 idi° topes (ids) expressed on the mouse anti- human CD4 mAb HP2/6 (Abl ). 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 expression. id 23 (defined by the anti-idiotypic mAb F11-2302) is likely to be "sequence dependent", since it is also expressed on SDS- and reducing reagent-treated separated heavy and, to a lower extent, light chains 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 studies suggested that id 23 displayed a markedly lower immunogenicity than 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 F16- 14D6, respectively, to HP2/6. The results suggest that differences in the Ig-chains distribution of ids may markedly influence their immunogenicity, and that id 23 does not appear to behave as a regulatory id, because it is private and less immunogenic than the conformational 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 antibody molecule could not be related to its regulatory role.