Sperm as activating cofactors in HIV sexual transmission

Researchers at the University of California at Los Angeles and at the National Institute for Immunology in New Delhi, India conducted parallel laboratory studies which indicate that sperm may augment HIV infectivity. The studies showed that HIV binds easily to sperm. Further, sperm infects target peripheral blood leukocytes (PBLs) proficiently. In addition, sperm binds to HLA-DR molecules which can transduce signals. Similar to what happens when an immobilized anti HLA-DR antibody binds with the surface of HLA-DR which in turn activates HLA-DR expressing cells, sperm binding with HLA-DR also activates HLA-Dr expressing cells. The sperm/HLA-DR binding serves to transduce receptor coupled signals and expands and divides target cells. Target cell activation increases HIV entry and initiates latency. Furthermore new virus replication needs activation. If indeed sperm can activate HLA-DR bearing cells, this may explain both sperm increased HIV infectivity observed for PBLs in vitro and the efficiency of semen for transmitting HIV in vivo. Besides, HLA-DR bearing cells exist in great numbers in the female reproductive tract. In fact, some even express the HIV receptor CD4. These results suggest that sperm play an important role in the microenvironment leading to HIV infection. They also emphasize the significance of spermicide use with condoms to protect against HIV transmission.