Chronically HIV-1 Infected Patients Exhibit Low Frequencies of CD25+ Regulatory T Cells

The characterization of regulatory T cells (Treg) during HIV infection has become of particular interest considering their potential role in the pathogenesis of the acquired immunodeficiency syndrome. Different reports on Tregs in HIV-infected patients vary greatly, depending on the state of disease progression, anatomical compartment, and the phenotypic markers used to define this cell subpopulation. To determine the frequency of Tregs we included paired samples from peripheral blood and rectal biopsies from controls and chronic HIV patients with or without detectable viral load. Tregs were determined by flow cytometry using three different protocols: CD4(+)Foxp3(+); CD4(+)Foxp3(+)CD127(Low/-), and CD4(+)CD25(+)CD127(Low/-). In addition, and with the purpose to compare the different protocols we also characterized Tregs in peripheral blood of HIV negative individuals with influenza like symptoms. Here, we report that Treg characterization in HIV-infected patients as CD4(+)Foxp3(+) and CD4(+)Foxp3(+)CD127(Low/-) cells was similar, indicating that both protocols represent a suitable method to determine the frequency of Tregs in peripheral blood mononuclear cells (PBMC) and gut associated lymphoid tissue (GALT). In contrast, in HIV but not in flu-like patients, detection of Tregs as CD4(+)CD25(+)CD127(Low/- )cells resulted in a significantly lower percentage of these cells. In both, HIV patients and controls the frequency of Treg was significantly higher in GALT compared to PBMC. The frequency of Tregs in PBMC and GALT using CD4(+)Foxp3(+) and CD4(+)Foxp3(+)CD127(Low/-) was higher in HIV patients than in controls. Similarly, the frequency of Treg using any protocol was higher in flu-like patients compared to controls. The results suggest that relying on the expression of CD25 could be unsuitable to characterize Tregs in PBMC and GALT samples from a chronic infection such as HIV.