Although more experimental data are needed to

resolve this question, epidemiological data documenting resistance in HESN sex workers suggests that repeated mucosal exposure and the associated cell infiltrates do not result in higher infectivity, but rather a sustained resistance against HIV-1 infection [1]. Further research utilizing animal models of SIV mucosal exposure would be helpful in elucidating if pathogen-induced DC activation at the site of exposure is associated with recruitment of NK cell activity and protection from HIV-1 infection in spite of the recruitment of CD4+ T cell targets. Most anti-viral mechanisms are expected to act both at preventing infection during exposure and in reducing viral replication after infection. However, adaptive Proteasome inhibitor T cell responses may be more effective at control of viral replication after infection, as memory responses are probably amplified as CD8 T cell effectors only after infection is established. In contrast, NK cells remain an immune cell type associated with both resistance

to HIV-1 infection in HESN subjects and control over viral replication following infection. The case for the anti-viral capacity of NK subsets during infection is suggested by its loss of function in chronic infection. Progressive HIV disease is associated clearly with increasingly DNA Damage inhibitor impaired NK responses and the selective depletion of CD56dim Tobramycin NK cells during chronic HIV-1 infection [112–115]. The loss of CD56dim NK cells, the main circulating NK subset that mediates cytotoxicity, results in the enrichment of CD56null NK cells with decreased function [113,116–118]. HIV-1 replication also results in the altered expression of inhibitory and activating receptors on NK cells further impairing the lytic potential of the remaining NK pool [119–121]. Defects in the NK cell compartment have been hypothesized to

be part of the profound immunodeficiency observed during chronic HIV-1 infection and host susceptibility to opportunistic infections [122]. In contrast, NK frequency and IFN-γ production have been shown to be retained in HIV-1 long-term non-progressors [123]. HIV-1-infected elite controllers that suppress viral replication in the absence of anti-retroviral therapy also exhibit NK activity that is comparable to uninfected control donors [124]. Together, these results correlate an increasingly dysfunctional NK cell compartment after infection with loss in control over HIV-1 replication during chronic infection. Genetic studies of the KIR3DL1 locus in disease progression studies indicate that inheritance of KIR3DS1 and KIR3DL1high receptor alleles in conjunction with their HLA ligands can delay disease progression [87,125]. These genotypes are the same as those observed to be over-represented in a high-risk cohort of HESN i.v. drug users and HESN partners of HIV-1-infected subjects [17,28].