Semen itself is clearly more than a vector for HIV-1. Seminal factors facilitating or inhibiting viral infection include cationic peptides with antiviral activity, cytotoxic MK-2206 in vivo molecules, amyloid fibrils derived from seminal phosphatases, complement fragments and prostaglandin E2 (PGE2) and bioactive peptides responsible for inducing mucosal inflammatory reactions (Table I). All of these interacting processes need to be considered to better understand HIV-1 mucosal transmission

and devise strategies for prevention. The effect of semen and seminal plasma (SP) warrants further investigation into in vitro and in vivo models of sexual transmission of HIV-1 to elucidate Daporinad their role, relevance, and mechanisms of action. It is thought that the oxidation of SP polyamines by diamine oxidase,21 augmented by peroxidases present in a healthy vaginal environment, produces radicals that inactivate HIV-1. The virus, in particular the lipids contained in its envelope, is highly sensitive to oxygen radicals.22 Semen produces reactive oxygen species,23 which can alter the infectivity of HIV. A normal healthy vagina also contains lactobacilli-produced hydrogen peroxide (H2O2), which maintains a low level of virucidal activity.24In vitro studies demonstrate that at concentrations

where H2O2-producing lactobacilli levels are not virucidal, the addition of peroxidase, such as myeloperoxidase or eosinophil peroxidase and a halide (chloride, iodide, bromide, thiocyanate), can restore anti-HIV-1 activity.25 Data from the 1970s also support that several viruses are inactivated by polyamine oxidation products.26–29

Cationic antimicrobial polypeptides, such as secretory leukoprotease inhibitor, defensins and lactoferrin, produced by mucosal surfaces from the oral and CV tracts, have been identified and found to have varying levels of antibacterial and anti-HIV-1 activity.30 O’Connor et al.31 demonstrated in vitro that semen, and specifically SP, had antiviral activity against HIV-1. Semen showed consistent activity against HIV-1, and the inhibitory concentration was between 35- and 50-fold lower than the cytotoxic concentration.31 In Bumetanide further experiments, Martellini et al.32 demonstrated that SP contained 52 individual cationic polypeptides, which contributed to its aggregate anti-HIV-1 activity, and that SP maintained anti-HIV-1 activity, even when diluted 3200-fold. However, this phenomenon was transient, as whole SP incubated for over 24 hr exhibited a reduction in anti-HIV-1 activity. In order for a male-to-female HIV-1 exposure to become a productive infection, the virus must cross an epithelial surface to interact with T lymphocytes, macrophages, and DCs, which are the main targets of infection.