MOLECULAR HETEROGENEITY OF ANTIGEN-INDUCED OR IDIOTYPE-INDUCED ANTITHYROGLOBULIN MONOCLONAL AUTOANTIBODIES

To define the molecular basis of the cognitive interaction in experime ntal autoimmune thyroiditis (EAT), we sequenced the variable regions o f monoclonal autoantibodies to thyroglobulin (Tg), specific or not for the F40D peptide, a Tg peptide capable of inducing EAT in CBA/J mice. Three MoAbs were obtained by immunization with syngeneic Tg of CBA/J (3B8G9, 2F6F2) or C57B1/6 (4D11F4) mice. 3B8G9 was specific for F40D p eptide, whereas 2F6F2 and 4D11F4 were not. Two others were raised in C BA/J mice by manipulation of idiotypic pathways: B12 resulted from the immunization with one Ab2 beta, bearing the internal image of one F40 D epitope, and TA2 from the immunization with F40D-specific cytotoxic HTC2 T cells. B12 and TA2 were both specific for F40D. All hybridomas expressed different members of the J558 V-H family, except 3B8G9 which expressed a Q52 V-H gene segment. These data led us to hypothesize th at regulatory anti-id autoantibodies used members of one V-H family lo cated in the 5'-end of the V-H locus, whereas EAT-associated autoantib odies used a member of one of the most D-proximal V-H family. As expec ted, no homologies were found when anti-F40D monoclonal autoantibodies were compared with two other monoclonal autoantibodies displaying a d ifferent epitopic specificity. Among the anti-F40D monoclonal autoanti bodies, one histidine residue located in position 35 of the CDR1 regio n was constantly found. Moreover, TA2 and B12 exhibited two common ani mo acids in their CDR3 regions, one glycine and one tyrosine, in posit ions 98 and 99, respectively. Striking homologies were found between T A2 and one anti-polyGAT MoAb, and between 3B8G9 and some anti-phenylox azolone (phOx) monoclonal autoantibodies. Lastly, the VK sequence from 4D11F4 was identical at the amino acid level to the VK sequence from another monoclonal autoantibody, 81B1, which was previously raised tow ards syngeneic Tg in CBA/J mice. Our data imply that anti-idiotypic re gulatory circuits in EAT might be generated by a heterogeneous populat ion of B cells rather than obtained by a single dominant B cell popula tion.