CD4(+)CD25(High) Treg cells in HIV/HTLV co-infected patients with neuropathy: high expression of Alpha4 integrin and lower expression of Foxp3 transcription factor

Abstract

Background: Regulatory CD4 T cells (Tregs) are critical in maintaining the homeostasis of the immune system. Quantitative or phenotypic alterations and functional impairment of Tregs have been associated with the development of pathologies including those of the central nervous system. Individuals with HIV-1/HTLV-1 co-infection are more prone to develop neurological complications. The aim of this study was to characterize phenotypically Treg cells in HIV-1/HTLV-1 co-infected Mozambican individuals presenting neurological symptoms.

Methods: A cross-sectional study was conducted among HIV-infected individuals presentingneurological symptoms, with and without HTLV co-infection, and blood donors. Peripheral bloodmononuclear cells were stained with monoclonal antibodies conjugated with fluorochromes to quantifyTregs and activated T cells by four colors flow cytometry.

Results: Higher Treg cell frequency (10.6%) was noted in HIV-1/HTLV-1 co-infected group with neurological symptoms when compared to HIV-1 mono-infected group with neurological symptoms (0.38%, p = 0.003) and control group (0.9%, p = 0.0105). An inverse correlation between Foxp3 and CD49d expression was observed in all study groups (rh = -0.71, p = 0.001). In addition, increased levels of Treg cells in co-infected patients were strongly associated with total activated CD4 T cells (rh = 0.8, p = 0.01).

Conclusion: Treg cells in co-infected patients present phenotypic alterations and might have dysfunction marked by low expression of Foxp3 and increased expression of molecules not frequently seen on Treg cells, such as CD49d. These alterations may be related to (1) changes in Treg cell trafficking and migration, possibly making those cells susceptible to HIV infection, and (2) inability to control the activation and proliferation of effector T lymphocytes.

Fig. 1

Expression of CD25 in CD4⁺ lymphocytes and representative analysis of FoxP3. In (a) dot plot representing the regions, CD4⁺CD25^Low and CD4⁺CD25^High. In (b) graphics representing the same regions in “a” in the different study groups control, HIV Neur and HIV/HTLV Neur. For each group we show the median of CD4⁺CD25^High cells, in relation to the total number of lymphocytes. In (c) histograms representatives of FoxP3 expression within the CD4⁺CD25^High region in the study groups. Control (n = 5): healthy individuals; HIV Neur (n = 8): HIV mono-infected group presenting neuropathy; HIV/HTLV Neur (n = 8): group co-infected by HIV-1 and HTLV-1 presenting neuropathy

Fig. 2

Frequency of Treg cells. Median of Treg cells (CD4⁺CD25^HighFoxp3⁺), expressed as percentage in relation of total number of lymphocytes, are shown for each group. Control (n = 4); HIV Neur (n = 7); HIV/HTLV Neur (n = 6). **p < 0.005

Fig. 3

Density of FoxP3 in CD4⁺CD25^High cells and their correlation with frequency of CD49d. In (a) median fluorescence intensity of CD4⁺CD25^High and CD4⁺CD25^Low cells from individuals of control (n = 4), HIV Neur (n = 7) and HIV/HTLV Neur (n = 6) groups. †, ‡ and ₣, difference statistically significant in relation to CD4⁺CD25^Low cells from control group, HIV Neur and HIV/HTLV Neur, respectively. Note that there is a significant difference in the density of Foxp3 expression between CD4⁺CD25^High and CD4⁺CD25^Low cells in the same group. In (b) frequency of CD49d in Treg cells. *p < 0.05, **p < 0.001. In (c) correlation between CD49d and density of FoxP3 expression in CD4⁺CD25^High cells, obtained as the median fluorescence intensity (MFI)

Fig. 4

Correlation between the frequency of Treg cells and CD4+ activated lymphocytes. In a, b and c, correlation between the frequency of Treg cells and CD4 activated cells (CD4⁺HLA-DR⁺) in control HIV Neur and HIV/HTLV Neur groups. Only in co-infected group a positive correlation was seen