Previous studies have shown that the frequency and absolute numbers of NK cells are decreased in chronic HIV infection and the function of remaining NK cells is impaired.32,33 In the current study, increased numbers of NK cells correlated GSK1120212 cost with increased NK cell function, and we found greater numbers of CD107+ NK cells in HSV-2 co-infected subjects. Of greatest interest is that the number of NK cells expressing the receptors NKp30, NKp46 and low-level KIR3D was strongly and inversely correlated with viral load in HIV-1-infected subjects. This suggests that increased numbers

of functional NK cells negatively impact HIV-1 viral load, and that NK cells might mediate some level of control of HIV-1, although this will require further study to determine causality and potential mechanisms. Conversely, in the context of HSV-2 co-infection, there are greater numbers of functional NK cells, yet this increase in NK cell functional capacity has no impact on HIV-1 viral load, as the correlation with the numbers of NK cells expressing activating receptors is lost. These data suggest a model whereby HSV-2 co-infection results in an increased number of functional BGJ398 NK cells, but this increased function is possibly directed towards HSV-2 at the expense of HIV-1 recognition and control. In this model, prophylactic control of HSV-2 infection may allow

NK cells to resume effective control of HIV-1 viraemia, resulting in reduced HIV-1 viral load. Importantly, however, we have not formally demonstrated either HIV-1 or HSV-2 specificity of NK cell function, leaving our results open to other interpretations. In previous studies Uroporphyrinogen III synthase of HSV-2 co-infection in HIV-1-positive subjects, reactivation of HSV-2 was associated with increased HIV-1 viral load, and was more common in subjects with lower CD4+ T-cell counts.21,34 Conversely, no significant correlation was observed between HIV-1 viral load and HSV-2 infection

in the absence of HSV-2 lesions. Subjects infected with HSV-2 are at greater risk for HIV-1 acquisition,35 providing the impetus for the study of HSV-2 prophylaxis in preventing HIV-1 infection. However, treatment with acyclovir has not been demonstrated to be effective in preventing HIV-1 acquisition in HSV-2-positive subjects,36 but was effective in reducing HIV-1 viral load in co-infected women.37 More recent evidence has shown that acyclovir itself strongly inhibits HIV-1 reverse transcriptase, and may account for the reduced HIV-1 viral load observed in response to HSV-2 prophylaxis.38 In the previous study evaluating CD4+ T-cell numbers in co-infected subjects by Barbour et al.,20 it was noted that subjects who had acquired HSV-2 prior to HIV-1 infection had elevated numbers of CD4+ T cells; however, this was not the case in subjects who acquired HSV-2 subsequent to HIV-1 infection.