Major antigenic region on the integrase (IN) protein of human immunodeficiency virus type 1 determined by reactivity of human sera and a monoclonal antibody to IN protein.

The gene encoding the integrase (IN) protein of human immunodeficiency virus type 1 (HIV-1) was expressed in vaccinia virus and Escherichia coli, and sera from 55 HIV-1-infected individuals were examined for immunoreactivity to the recombinant IN proteins by Western immunoblot. Approximately 98% (54 of 55) of the HIV-1-infected individuals showed reactivity to both the full-length IN protein of 32 kDa (IN32 protein) and the carboxy-terminal portion of the IN protein (IN17 protein). Serum samples from only 6 of the 54 antibody-positive individuals and a monoclonal antibody against the IN protein, 6F4, reacted with the amino-terminal portion of the IN protein (IN15 protein). The eight AIDS patients tested were seronegative to IN15 protein. The magnitude of reactivity to the recombinant IN proteins decreased slightly in the progression of the course of HIV-1 infection. These results suggest that a B-cell immunodominant epitope(s) on the IN protein is located on the C-terminal IN17 portion and that a minor epitope(s) recognizable by 6F4 and by rare patients is on the N-terminal IN15 portion.