Longitudinal study of homosexual couples discordant for HIV-1 antibodies in the Baltimore MACS Study.

Thirty-six sexually active couples serologically discordant for human immunodeficiency virus, type 1 (HIV-1), within the Baltimore Multicenter AIDS Cohort Study (MACS) were assessed to determine whether evidence of HIV-1 infection could be detected in the HIV-1-antibody-negative partners and whether factors associated with lack of transmission of HIV from the seropositive to the seronegative partner could be ascertained. Six HIV-1 seropositive couples and 18 seronegative couples were followed concurrently for comparison. None of the seropositive subjects had an AIDS-defining illness at entry into the study, and all subjects were followed for 1 year. A separate evaluation of unprotected anal receptive and insertive intercourse between discordant couples indicated high-risk activities for a median of 40 months, as reported by the HIV seropositive partner. Despite this finding, none of the HIV-1 seronegative men in discordant couples had evidence of HIV-1 infection by viral culture, p24 antigen testing, or polymerase chain reaction for HIV-1 DNA. Discordant seronegatives and seropositives did not differ from concordant seronegatives and seropositives in numbers of circulating CD4, CD8, and natural killer lymphocytes or in prevalence of antibodies to herpes simplex virus, type 1, Epstein-Barr virus, or cytomegalovirus, except that discordant seronegative men were less likely than their seropositive partners to have antibodies to herpes simplex virus, type 2. The reason for the apparent lack of HIV-1 infection in seronegative discordant individuals remains unexplained and did not appear to be associated with type of sexual activity, T-lymphocyte subsets or natural killer cells, or early stage of HIV-1 disease.