Sperm Cells, in Addition to Semen, May Play a Role in Sexual Transmission of HIV

It is well known that semen can transmit HIV during sexual activity, but sperm cells themselves appear able to capture and transport the virus to vulnerable dendritic cells, according to study results published in the November 23, 2009 Journal of Experimental Medicine.

Semen, which is the major route of HIV transmission worldwide, contains 3 major sources of infectious virus: free virions (virus particles), infected leukocytes (white blood cells), and spermatozoa-associated virions, Ana Ceballos from the Universidad de Buenos Aires in Argentina and colleagues noted as background.

The investigators focused on the interaction of HIV-1 with human spermatozoa (individual sperm cells) and dendritic cells, a type of immune system cell that captures invading pathogens and presents them for recognition by T-cells.

The authors reported that heparan sulfate is expressed on spermatozoa and plays an important role in enabling the HIV envelope to attach to the sperm cell surface. This spermatozoa-attached virus can then be efficiently transmitted to dendritic cells, macrophages, and T-cells. CD4 and DC-SIGN receptors on dendritic cells were required for transmission, suggesting that the cells capture the virus by binding to sperm, rather than by engulfing or ingesting them.

Interaction of spermatozoa with dendritic cells not only leads to the transmission of HIV and the internalization of the spermatozoa, they continued, but also results in the maturation of dendritic cells and production of interleukin 10 (IL-10), a cytokine that plays a role in suppressing inflammation, which might help the virus to spread.

The researchers determined that the binding of HIV to spermatozoa and the subsequent transmission of virus to dendritic cells was strongly enhanced at low (acidic) extracellular pH values similar to those found in the vagina after sexual intercourse.

"Our observations support the notion that far from being a passive carrier, spermatozoa acting in concert with dendritic cells might affect the early course of sexual transmission of HIV-1 infection," the investigators concluded.

Centro Nacional de Referencia para el SIDA, Facultad de Medicina, Universidad de Buenos Aires, Buenos Aires, Argentina; Instituto de Investigaciones Hematológicas, Academia Nacional de Medicina, Buenos Aires, Argentina; Instituto Médico Halitus, Buenos Aires, Argentina; Instituto de Biología y Medicina Experimental, Buenos Aires, Argentina; Institut National de la Sante et de la Recherche Medicale, Immunite et Cancer, Institut Curie, Paris, France.

12/15/09

Reference

A Ceballos, F Remes Lenicov, J Sabatté, and others. Spermatozoa capture HIV-1 through heparan sulfate and efficiently transmit the virus to dendritic cells. Journal of Experimental Medicine 206(12): 2717-2733 (Abstract). November 23, 2009.