Do chemokines play a role in HIV-1 heterosexual transmission? Susceptibility to HIV infection.

The probability of HIV transmission depends on the infectiousness of the infected partner, the susceptibility of the healthy partner, and the biological characteristics of HIV strains. A substantial role is attributable to the individual HIV susceptibility, which is affected by immunological and genetic factors. Among genetic factors, the chemokine receptor CCR5 has been thoroughly studied. CCR5 is a co-receptor for fusion and entry of macrophage-tropic variants of HIV-1, which are involved in sexual transmission. Consistent evidence shows that the absence of cell-surface expression of the HIV co-receptor CCR5, due to a homozygous 32 base pair deletion, renders individuals highly resistant to infection by macrophage-tropic HIV strains. Therefore, knowledge of this and of other genetic and immunologic factors that affect HIV-1 transmission is essential in understanding HIV-1 entry into cells, developing strategies for combating HIV-1 transmission and spread, and implementing new models for HIV-1 therapies and, hopefully, vaccines.