The impact of sex work on the susceptibility to HIV infection among HIV resistant sex workers

Abstract

Background: Commercial sex workers are at high risk of HIV acquisition especially in countries with high HIV prevalence. In Kenya, over 10% of all new HIV infections have been attributed to sex workers and their clients. Unprotected sex results in exposure of the female genital tract to sex- derived antigens present in semen. Studies have reported a post-coital inflammatory response to these antigens in animals and humans.In vivo, such inflammatory response leads to recruitment of activated leukocytes including T cells from the peripheral circulation to the genital mucosa where they can be infected by HIV. There is need to explore the impact of sex work on the activation of the immune system and its role in the transmission of HIV.HIV-exposed seronegative (HESN) female sex workers have been shown to have lower peripheral and mucosal immune activation than their HIV- positive counterparts or HIV- uninfected low risk women. This reduced immune activation state is thought to be protective against HI V infection. It is, therefore, thought that HESN sex workers are able to down regulate sex- work- induced immune activation by a yet unknown mechanism. Hypothesis: This study hypothesized that sex work results in exposure to very strong immune stimulants which can drive systemic immune activation and that HESN women are able to down regulate this sex work- driven immune activation more efficiently than HIV susceptible controls. Objective: The study was designed to characterize the impact of sex work on activation and phenotype of peripheral T cells, among female sex workers at the Pumwani Clinic, Nairobi. Methods: Thirty female sex workers were recruited; 10 in each arm of HESN, HIV- positive, and New Negatives. Blood samples were obtained from them when in active sex work, during a sex break and upon return to sex work. PBMCs were extracted from the blood and stained with a 10-colour monoclonal antibody panel for phenotypic (CD3, CD4, CD8, CD45RA, CD161), trafficking (CCR7, CCR5) and activation markers (CD69, HLA-DR, CD95) of T cells. Expression of these markers was then evaluated by flow cytometry. Statistical analyses were done to compare the expression of T cell activation markers and memory phenotypes within each group during sex work, sex break and upon return to sex work. The difference in response to interruption of sex work was also assessed across groups. Results: A reduction in CCR5 expression on CD8+ T cells in HIV- positive sex workers was observed upon taking a break from sex work. A trend toward increase dexpression of CD161 on 10 CD4+ T cells was also observed in the HIV-positive. In New Negatives, we observed a trend towards decreased naïve CD8+ T cells during the sex break and upon return to sex work. It was also observed that there is no difference in the pattern of response to the interruption of sex work between HESN female sex workers and their HIV- positive and New Negative counterparts. Overall, HIV- positive women had higher frequency of effector memory T cells and CD95 express in g CD8+ T cells and a lower frequency of naïve CD8+ T cells than HESN and New Negatives. Conclusion: Sex work had a subtle effect on the expression of T cell activation markers and memory phenotypes in the peripheral compartment. Interruption of commercial sexual activity had a greater impact on T cell activation in HIV-positives. In HESN and New Negatives, sex work had no discernible effect on peripheral immune activation. No apparent difference in the way HESN, HIV- positive and New Negative sex workers respond to interruption of sex work was observed, which may be due to various limitations of this study. Therefore, the impact of sex work could be confined to the FGT mucosa and not be reflected in the peripheral compartment