The molecular origin of regulatory idiotypes.

A complete immunochemical and molecular profile was generated for a group of hybridoma and myeloma antibodies bearing the A48 regulatory idiotype (RI). These A48 RI+ antibodies were derived from normal or idiotypically manipulated mice and were selected either for utilization of a VHX24 VH gene or expression of the A48 RI. Among the hybridomas selected for VHX24 VH utilization a variety of antibody specificities were seen with the fructosan specificity occurring least frequently and the N-acetylglucosamine specificity occurring most frequently. A variety of Vk families were used with a bias for the Vk1 family by the antibodies deriving from untreated mice. The A48RI was expressed by only 3 of these antibodies, none of which were fructan specific. Two used the canonical VHX24-Vk10 combination utilized by the A48 and UPC 10 prototypes, and one used the VHX24-Vkl combination. This demonstration of A48 RI expression ny non-fructan specific, non-VHX24+Vk10+ antibodies was extended by showing expression of this Id by two monoclonal antibodies specific for the Sm self-antigen, one rheumatoid factor and two monoclonal antibodies specific for influenza virus hemagglutinin molecule. They used different VH-VL combinations. Among the monoclonal antibodies selected for A48 RI expression all exhibited fructan binding activity and the vast majority used the VHX24-Vk10 association. A collective analysis of the VH and VL sequences of all these A48RI+ antibodies showed idiotype expression was not associated with any particular germline VH or VL gene. D, Jk or JH sequence. Three positions on the light chain and one on the heavy chain were identified which could represent the structural correlates for the A48 regulatory idiotype.