Osmond J. D'Cruz, Ph.D

Section of Reproductive Endocrinology and Infertility, Department of Obstetrics and Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73190

6. SPERM-OOCYTE FUSION AND TRANSMISSION OF HIV

Sperm-oocyte fusion may serve as a vehicle for transfer of dormant viruses to oocytes. This transmission occurs by two different pathways to the ovulated ova. Viral entry may occur directly via fertilizing sperm. Alternately, virus entry into the oocyte may take place by viruses released from other sperm during acrosome reaction. Recent evidence suggests that sexual transmission of human immunodeficiency virus (HIV) can be mediated via sperm-oocyte fusion (105). HIV particles have been detected on and around organelles in mature sperm either ejaculated by AIDS patients or incubated in vitro with HIV. In the first case, the nucleoid of the virus can be devoid of an envelope or is enveloped by a membrane-like coat. These viral particles bud from the plasma membrane. In the in vitro infected sperm, only membrane enveloped nucleoids are present. Baccetti and co-workers suggest that HIV particles penetrate sperm from AIDS patients in various stages of development. During different stages of sperm development, viral particles replicate and bud through the plasma membrane. In contrast, in vitro infected sperm, only display penetrated viral particles and do not exhibit buddings and membrane-free nucleoids. Baccetti and co-workers using immunoelectron microscopy, in situ hybridization, and polymerase chain reaction technique, showed that HIV-1 binds and enters normal sperm (106). Presence of viral particles, their antigens, and nucleic acid were shown in sperm of HIV-1 infected men. These sperm could transfer HIV-1 like particles to normal human oocytes (106). It was suggested that galactosylceramide-like compound on the sperm membrane could function as a receptor for HIV (106).

Scofield and co-workers demonstrated that sperm/leukocyte-mediated cell interactions are dependent on HLA class II molecules expressed on leukocytes (107). Sperm receptor activity requires presence of sulfated carbohydrates as carriers for HLA-DR binding ligands. Scofield and associates demonstrated that sperm can bind HIV through the mechanism related to class II MHC-CD4 molecules (106-111). A CD4-binding glycoprotein (17.5 kDa) has been purified from human seminal plasma (110). This glycoprotein may act on the sperm as a receptor for the HIV-1.