T lymphocytes and macrophages, but not motile spermatozoa, are a significant source of human immunodeficiency virus in semen.

The cellular fraction of semen contains spermatozoa, immature germ cells, leukocytes, and epithelial cells. Recent evidence implicates seminal cells as a major source of sexually transmitted human immunodeficiency virus (HIV) in semen, but the identity and infectious potential of infected cells remains poorly understood. HIV provirus was found in 75% of viable semen cell samples by polymerase chain reaction and in 88% of paired blood cell samples from HIV-seropositive men. When semen cell subpopulations were isolated by an immunomagnetic bead technique, T cells were found to be most commonly HIV-infected (75% of samples), followed by macrophages (38% of samples). Viral DNA was never detected in motile spermatozoa or immature germ cell populations. Semen leukocytes proliferated in response to mitogenic and antigenic challenge and produced p24 following stimulation with irradiated allogeneic cells. These data provide evidence that both T cells and macrophages, but not germ cells, are cellular vectors of HIV transmission in semen.