A new study has shown that HIV can be transmitted by sperm and not just semen.
It is well known that during sexual intercourse, HIV-infected men transmit HIV through their semen, which carries free-floating virus as well as HIV-infected leukocytes.
However, lead researcher Ana Ceballos at the University of Buenos Aires in Argentina claims that sperm can also transmit HIV to macrophages, T cells, and dendritic cells (DCs).
Ceballos et al. showed that HIV attaches to the surface of sperm and that these HIV carriers pass on the virus to DCs and other HIV targets.
Sperm express molecules known to interact with HIV's envelope, such as heparan sulfate and mannose receptors.
The authors show that HIV relies on heparan sulfate to attach to sperm, but not mannose receptors as previously predicted.
Once attached, the virus was transmitted from sperm to DCs in culture. The DC receptors CD4 and DC-SIGN were required for transmission, suggesting that DCs pick up the virus by binding to sperm rather than by ingesting them.
DCs matured after interacting with the sperm, producing tolerance-promoting cytokines like interleukin-10. The authors speculate that this immune-suppressing profile, versus an inflammatory profile, might also help the virus spread.
The authors suggest that sperm might reach DCs by passing through microabrasions in the vaginal or anal lining that often form during intercourse.
The study appears in Journal of Experimental Medicine.