Lactoferrin, a component of

breast milk and genital secretions, has also been shown to inhibit HIV-1 Sirolimus replication and transmission from dendritic cells (DCs) to T cells in vitro[70–72]. Nevertheless, cervicovaginal levels of lactoferrin, RANTES and SLP1 were tested in HIV-1 seronegative women at a high risk of heterosexual acquisition of HIV infection and were found to be associated with bacterial vaginosis and inflammation rather than exposure to HIV-1 [73]. In contrast, elafin/trappin-2 was found to be elevated in the female genital tract of HESN Kenyan sex workers and was associated with protection against HIV-1 acquisition [74]. Defensins represent a family of small cationic peptides expressed in the mucosal epithelium with broad anti-microbial properties against HIV-1 and other sexually transmitted diseases relevant to HIV-1 transmission [75]. Both α-defensins and Bioactive Compound Library β-defensins have been associated repeatedly with

protection in several independent studies of HESN subjects [76–80]. This includes the description of alpha-defensins in the prevention of HIV transmission among breastfed infants [76] and the identification of elevated levels of both alpha and beta-defensins in sexually HIV-1 exposed but uninfected individuals [79,80]. Despite potent HIV inhibitory activity, however, cervicovaginal levels of α-defensins have also been associated with increased HIV acquisition due to their association with bacterial sexually transmitted infections [81]. The role of α-defensins in HIV-1 vertical transmission remains contentious, with one study showing no association between α-defensin concentration in breast milk and risk of HIV-1 transmission [82] while another study showed the opposite [76]. Overall, the varied secreted proteins identified in the mucosa of HESN subjects (summarized in Table 2) may represent true factors associated with reducing

mucosal transmission of HIV-1 infection. Rather, they may reflect the innate immune response to genital tract inflammation due to ongoing bacterial infections or sexually transmitted diseases, which may be endemic in the case of sex worker mafosfamide cohorts. Taking the data as a whole, we interpret that soluble innate factors are likely to modulate the infectivity threshold for HIV-1 upon exposure. However, secreted anti-viral factors alone are unlikely to render a complete barrier to infection, and innate immune cells such as natural killer (NK) cells and DCs may also bolster the threshold to infection that HIV-1 must overcome. NK cells represent a critical component of the host innate immune response against viral infection and serve as a front-line defence against a diverse array of pathogens.