HIV-specific IL-10+ CD8+ T cells were present at low frequencies in the peripheral blood in our study cohort (median 0.01% in ART-naïve individuals), whereas the dual IL-10-/IFN-γ-secreting CD4+ Tr1-like cells described by Haringer et al. [19] comprised approximately 1% of antigen-experienced (CD45RAneg) CD4+ T cells. The size of this population reflected its composition of many different antigen specificities, whereas the population we identified was specific for a single HIV-1 antigen and its frequency was expressed as a percentage of the entire CD8+ T-cell subset (as opposed to antigen-experienced cells only). Furthermore, the expression of beta-7 integrin and CXCR3 would

endow this population with the capacity GSK1120212 purchase to home to GALT and other sites of inflammation. This suggests JAK inhibitor that they could play a role in limiting virus-driven immune activation, as GALT is a major site of HIV-1 replication throughout infection [29]. It should also be noted that the contribution of HIV-specific CD8+ T cells to overall IL-10 production is considerable, despite a recent report finding that CD14+

monocytes were the major source of spontaneous IL-10 production in uncontrolled HIV-1 infection [8], as the data reported by Kwon et al. did not take into account the greater (typically approximately fivefold) absolute numbers of lymphocytes than monocytes in the peripheral blood. The capacity NADPH-cytochrome-c2 reductase to secrete IL-10 suggested that HIV-specific CD8+ T cells may have an immunoregulatory role. Conventionally, this is demonstrated by the capacity to inhibit the proliferation or cytokine secretion of other T-cell populations in vitro. However, such assays typically employ non-physiological suppressor/responder ratios. An alternative approach that has been used previously is to deplete the putative

regulatory population and examine the effects of its removal on responder cells [30, 31]. In view of the low frequencies of HIV-specific IL-10+ CD8+ T cells, we considered the latter approach to be more physiological. The enhanced proinflammatory responses by monocytes that were revealed by selective depletion of HIV-specific IL-10+ CD8+ T cells suggested that IL-10 production by HIV-specific CD8+ T cells could constitute an adaptive response to virus-driven monocyte activation. The simultaneous upregulation of CD38 and increased IL-6 production is intriguing and may reflect induction of IL-6 in monocytes as a direct result of CD38-mediated signalling, possibly triggered by a viral ligand [32]. Recently, Andrade and colleagues [33] demonstrated that antibody blockade of IL-10 signalling in PBMCs from HIV-infected individuals resulted in increased expression of IL-6 following stimulation with HIV-1 envelope protein peptides. Our data extend these findings by suggesting that a specific population of HIV-specific CD8+ T cells may have the capacity to alter IL-6 expression in this way.