Background:  Many evidences support the role of T regulatory cells (Treg) in the pathogenesis of HIV infection and in the progress of tuberculosis disease (TB). In our survey we prospectively analyse Treg dynamics in HIV⁺ patients affected by TB at disease diagnosis and during therapeutic follow-up.

Methods:  We enrolled 20 patients and subdivided in 4 groups:  HIV/TB co-infected, HIV⁺; HIV^– affected by TB and HIV^– PPD⁺ health controls. Peripheral lymphocytes were stained with FITC conjugated anti-CD4 and PE conjugated anti CD25 and the percentage of CD4⁺CD25^bright was analysed by flow cytometry. The CD4⁺CD25^bright, CD4⁺CD25^dim and CD4⁺CD25^– populations were purified by cell sorting. Total RNA was extracted from different CD4⁺ sorted populations, retrotranscripted in cDNA and used for FOXP3, interleukin (IL) -10, and TGF-b gene expression analysis using real-time polymerase chain reaction. Different subpopulations were assessed for their proliferative capacity  in response to polyclonal and to MTB specific stimulations.

Results:  CD4⁺CD25^bright Tcells isolated were characterized by a higher expression of FOXP3 mRNA respect to CD25^dim and CD25^–CD4⁺Tcells. Analysis of CD4⁺CD25^bright percentage on CD4Tcells at baseline showed a lower level of Treg in HIV/TB co-infected patients (median 1%, IQR 1 to 1.3) with respect to HIV⁺ patients, TB patients, and HIV^– health donors (median, respectively, 2.3%, IQR 2 to 4); 2.1%, IQR 1.8 to 6.6; 1.9%, IQR 1.5 to 2.2). During therapy (anti-TB/HAART) HIV/TB-co-infected patients showed a median increase of 2.2 (IQR 0.65 to 3.45) in Treg percentage, while HIV^– patients affected by TB showed a median decrease of –0.2 (IQR–5 to 1.8). After 6 months HIV⁺ patients reached a significant higher frequency of Treg with respect to HIV^– patients (median percentage, respectively, 7.0%, IQR 5.0 to 8.3 and 2.0%, IQR 1.5 to 2.5; p = 0.0056). Proliferation assay in patients affected by TB showed an increase of MTB-specific proliferative response in CD4⁺CD25^bright depleted subpopulation respect to polyclonal proliferative response, supporting a strong MTB specific suppressor effect of CD4⁺CD25^brightT cells.

Conclusions:  TB in HIV⁺ patients is associated with a reduction in peripheral Treg followed by a subsequent increase during specific therapy. This trend differs from HIV^– patients affected by TB and suggests a possible role of Treg compartment in the pathogenesis of TB and in the more rapid HIV progression in co-infected patients.