Shuzo Matsushita

Induction of antibodies (Abs) against the conformational CD4‐induced (CD4i) epitope is frequent in HIV‐1 infection. However, the mechanism of development of anti‐CD4i Abs is unclear. We used anti‐idiotypic (aID) monoclonal Abs (mAbs) of anti‐CD4i mAbs to isolate anti‐CD4i mAbs from infected subjects and track the causative antigens. One anti‐aID mAb sorted from infected subjects by aID mAbs had the characteristics of anti‐CD4i Abs, including IGHV1‐69 usage and ability to bind to HIV‐1 Env enhanced by sCD4. Critical amino acid sequences for the binding of six anti‐aID mAbs, with shared idiotope to anti‐CD4i mAbs, were analysed by phage display. The identified amino acid sequences showed similarity to proteins from human microbiota and infectious agents. Peptides synthesized from Caudoviricetes sp and Vibrio vulnificus based on the identified sequences were reactive to most anti‐aID and some anti‐CD4i mAbs. These results suggest that anti‐CD4i Abs may evolve from B cells primed by microorganisms.