Background Cross-sectional studies have found a high prevalence of syphilis and HIV infection among men who have sex with men (MSM) in China. Methods A total of 218 HIV-negative MSM participated in this prospective cohort study. Interviewer-administered questionnaires were completed, and blood samples were obtained for HIV and syphilis testing, both upon enrollment and at 12-month follow-up. Results Of enrolled participants, 56% (122) were retained for the full 12-month follow-up period. The cohort had an HIV incidence density of 5.4 (95% CI: 2.0–11.3)/100 person-year (PY) and a syphilis incidence density of 38.5(95% CI: 27.7–50.2)/100 PY. Having syphilis (odds ratio [OR]: 11.4, 95% CI: 1.2–104.7) and more than 5 male sexual partners within the past 12 months (OR: 6.5, 95% CI: 1.1–39.8) were independent risk factors for HIV seroconversion (each P < 0.05). Being married (OR: 3.5, 95% CI: 1.4–8.2) and having more than 5 male sexual partners within the past 12 months (OR: 4.7, 95% CI: 2.0–6.2) were risk factors for syphilis seroconversion, while age ≥30 (OR 2.1, 95% CI 0.7–9.5) and having recently engaged in unprotected receptive anal sex (OR: 2.4, 95% CI: 0.7–13.1) were marginally associated with syphilis seroconversion. Conclusion The high incidence rates of HIV and syphilis in the Shenyang MSM community are significant cause for concern. The seroconversion rate for syphilis, in particular, indicates the high prevalence of high-risk sexual behaviors and the potential for increased HIV transmission. Appropriate interventions that address MSM-specific issues, including stigma, pressures from traditional society, and bisexual behavior, need to be tailored to inform and empower MSM in order to prevent HIV and syphilis in this community.

Natural killer (NK) cells are important for maintenance of innate immune system stability and serve as a first line of defense against tumors and virus infections; they can act either directly or indirectly and are regulated via co-operation between inhibitory and stimulatory surface receptors. The recently reported inhibitory receptor, TIGIT, can be expressed on the NK cell surface; however, the expression level and function of TIGIT on NK cells during HIV infection is unknown. In this study, for the first time, we investigated the expression and function of TIGIT in NK cells from HIV-infected individuals. Our data demonstrate that the level of TIGIT is higher on NK cells from patients infected with human immunodeficiency virus (HIV) compared with HIV-negative healthy controls. TIGIT expression is inversely correlated with CD4+ T cell counts and positively correlated with plasma viral loads. Additionally, levels of the TIGIT ligand, CD155, were higher on CD4+ T cells from HIV-infected individuals compared with those from healthy controls; however, there was no difference in the level of the activating receptor, CD226, which recognizes the same ligands as TIGIT. Furthermore, TIGIT was found to specifically up-regulated on CD226+ NK cells in HIV-infected individuals, and either rIL-10, or rIL-12 + rIL-15, could induce TIGIT expression on these cells. In addition, high TIGIT expression inhibited the production of interferon-gamma (IFN-γ) by NK cells, while TIGIT inhibition restored IFN-γ production. Overall, these results highlight the important role of TIGIT in NK cell function and suggest a potential new avenue for the development of therapeutic strategies toward a functional cure for HIV.