Proliferation and foxp3 expression in virus-specific memory CD8+ T lymphocytes

Histone Modulation Blocks Treg-Induced Foxp3 Binding to the IL-2 Promoter of Virus-Specific CD8⁺ T Cells from Feline Immunodeficiency Virus-Infected Cats

CD8⁺ T cells are critical for controlling HIV infection. During the chronic phase of lentiviral infection, CD8⁺ T cells lose their proliferative capacity and exhibit impaired antiviral function. This loss of CD8⁺ T cell function is due, in part, to CD4⁺CD25⁺ T regulatory (Treg) cell-mediated suppression. Our research group has demonstrated that lentivirus-activated CD4⁺CD25⁺ Treg cells induce the repressive transcription factor forkhead box P3 (Foxp3) in autologous CD8⁺ T cells following co-culture. We have recently reported that Treg-induced Foxp3 binds the interleukin-2 (IL-2), interferon-γ (IFN- γ), and tumor necrosis factor-α (TNF-α) promoters in virus-specific CD8⁺ T cells. These data suggest an important role of Foxp3-mediated CD8⁺ T cell dysfunction in lentiviral infection. To elucidate the mechanism of this suppression, we previously reported that decreased methylation facilitates Foxp3 binding in mitogen-activated CD8⁺ T cells from feline immunodeficiency virus (FIV)-infected cats. We demonstrated the reduced binding of Foxp3 to the IL-2 promoter by increasing methylation of CD8⁺ T cells. In the studies presented here, we ask if another form of epigenetic modulation might alleviate Foxp3-mediated suppression in CD8⁺ T cells. We hypothesized that decreasing histone acetylation in virus-specific CD8⁺ T cells would decrease Treg-induced Foxp3 binding to the IL-2 promoter. Indeed, using anacardic acid (AA), a known histone acetyl transferase (HAT) inhibitor, we demonstrate a reduction in Foxp3 binding to the IL-2 promoter in virus-specific CD8⁺ T cells co-cultured with autologous Treg cells. These data identify a novel mechanism of Foxp3-mediated CD8⁺ T cell dysfunction during lentiviral infection.

T Regulatory Cell Induced Foxp3 Binds the IL2, IFNγ, and TNFα Promoters in Virus-Specific CD8+ T Cells from Feline Immunodeficiency Virus Infected Cats

Polyfunctional CD8⁺ T cells play a critical role in controlling viremia during AIDS lentiviral infections. However, for most HIV-infected individuals, virus-specific CD8⁺ T cells exhibit loss of polyfunctionality, including loss of IL2, TNFα, and IFNγ. Using the feline immunodeficiency virus (FIV) model for AIDS lentiviral persistence, our laboratory has demonstrated that FIV-activated Treg cells target CD8⁺ T cells, leading to a reduction in IL2 and IFNγ production. Furthermore, we have demonstrated that Treg cells induce expression of the repressive transcription factor, Foxp3, in CD8⁺ T cells. Based upon these findings, we asked if Treg-induced Foxp3 could bind to the IL2, TNFα, and IFNγ promoter regions in virus-specific CD8⁺ T cells. Following coculture with autologous Treg cells, we demonstrated decreased mRNA levels of IL2 and IFNγ at weeks 4 and 8 postinfection and decreased TNFα at week 4 postinfection in virus-specific CD8⁺ T cells. We also clearly demonstrated Treg cell-induced Foxp3 expression in virus-specific CD8⁺ T cells at weeks 1, 4, and 8 postinfection. Finally, we documented Foxp3 binding to the IL2, TNFα, and IFNγ promoters at 8 weeks and 6 months postinfection in virus-specific CD8⁺ T cells following Treg cell coculture. In summary, the results here clearly demonstrate that Foxp3 inhibits IL2, TNFα, and IFNγ transcription by binding to their promoter regions in lentivirus-specific CD8⁺ T cells. We believe this is the first description of this process during the course of AIDS lentiviral infection.

Modulating DNA methylation in activated CD8+ T cells inhibits regulatory T cell-induced binding of Foxp3 to the CD8+ T Cell IL-2 promoter

We have previously demonstrated that CD4(+)CD25(+) regulatory T cells (Tregs) activated during the course of feline immunodeficiency virus (FIV) infection suppress CD8(+) CTL function in a TGF-β-dependent fashion, inhibiting IFN-γ and IL-2 production and inducing G1 cell-cycle arrest. In this article, we describe the molecular events occurring at the IL-2 promoter leading to suppression of IL-2 production. These experiments demonstrate that Foxp3 induced by lentivirus-activated Tregs in the CD8(+) target cells binds to the IL-2 promoter, actively repressing IL-2 transcription. We further demonstrate that the chronic activation of CD8(+) T cells during FIV infection results in chromatin remodeling at the IL-2 promoter, specifically, demethylation of CpG residues. These DNA modifications occur during active transcription and translation of IL-2; however, these changes render the IL-2 promoter permissive to Foxp3-induced transcriptional repression. These data help explain, in part, the seemingly paradoxical observations that CD8(+) T cells displaying an activation phenotype exhibit altered antiviral function. Further, we demonstrate that blocking demethylation of CpG residues at the IL-2 promoter inhibits Foxp3 binding, suggesting a potential mechanism for rescue and/or reactivation of CD8(+) T cells. Using the FIV model for lentiviral persistence, these studies provide a framework for understanding how immune activation combined with Treg-mediated suppression may affect CD8(+) T cell IL-2 transcription, maturation, and antiviral function.

Deregulation from CD4+ memory T cells to regulatory cells in patients with chronic renal failure: a pilot study

BACKGROUND

The aim of this study was to elucidate whether the CD4+ memory T (Tm) cells differentiation to regulatory T cells (Tregs) play a role in the immunological defects in patients with chronic kidney disease (CKD), and if the oxidized low-density lipoprotein (oxLDL) had affect on on CD4+ Tm cells and Tregs apoptosis in these subjects.

METHODS

CD4+ Tm cells and Tregs were detected by flow cytometry in each group of ten subjects. Apoptosis was measured by flow cytometry and confirmed by Western blotting.

RESULTS

The oxLDL concentration was significantly higher in CKD stage 4 (CKD4) patients than in controls, particularly in hemodialysis (HD) subjects (P < 0.001, respectively). In total, 100 μg/ml oxLDL significantly inhibited the CD4+ Tm cell proliferation. oxLDL-induced Tm generated Tregs apoptosis in controls and CKD4 patients, especially in HD patients (P < 0.001, respectively).

CONCLUSION

Dysregulation of CD4+ Tm cells converting into Tregs played a role in the immune defects of CKD patients, and oxLDL induced the apoptosis of Tm generating Tregs in these subjects. Larger size of sample should be investigated to confirm the findings in further studies.

Immunophenotype of skin lymphocytic infiltrate in patients co-infected with Mycobacterium leprae and human immunodeficiency virus: a scenario dependent on CD8+ and/or CD20+ cells

BACKGROUND

Leprosy occurs rarely in human immunodeficiency virus (HIV)-positive patients. In contrast to tuberculosis, there has been no report to date of an increase in HIV prevalence among patients with leprosy or of differences in leprosy's clinical spectrum. While several studies describe the systemic immune response profile in patients co-infected with HIV and leprosy, the local immune skin response has been evaluated in only a small number of case reports and limited series of patients.

OBJECTIVE

To investigate the interaction between Mycobacterium leprae and HIV infection in the skin.

METHODS

We investigated the presence and frequency of cells positive for CD4, CD8, CD20, TIA-1, FOXP3 and CD123 in lymphocytic infiltrates from 16 skin biopsies taken from 15 patients with HIV-leprosy co-infection.

RESULTS

CD4+ cells were absent in infiltrates from 6 (38%) skin biopsies and present in 10 (62%) cases at low levels (<1·16%) of the lymphocytic infiltrate. CD8+ was the predominant phenotype in the infiltrate (99·4%), followed by TIA-1, expressed by >75% of CD8+ cells. FOXP3+ cells were also present, representing 3·4% of the lymphocytic infiltrate. CD20+ cells were detected in 75% of the cases; however, in two cases (12%) these cells represented 25-50% of the infiltrate, while in the other 10 cases (62%) they were present only focally (<25% of the infiltrate). CD123+ cells were not observed in any of the studied specimens.

CONCLUSIONS

Data presented here suggest that cell-mediated immune responses to M. leprae are preserved at the site of disease and that in the absence of CD4+ cells, CD8+FOXP3+ and CD20+ cells may be involved in granuloma formation.

FOXP3 expression is upregulated in CD4T cells in progressive HIV-1 infection and is a marker of disease severity

Background

Understanding the role of different classes of T cells during HIV infection is critical to determining which responses correlate with protective immunity. To date, it is unclear whether alterations in regulatory T cell (Treg) function are contributory to progression of HIV infection.

Methodology

FOXP3 expression was measured by both qRT-PCR and by flow cytometry in HIV-infected individuals and uninfected controls together with expression of CD25, GITR and CTLA-4. Cultured peripheral blood mononuclear cells were stimulated with anti-CD3 and cell proliferation was assessed by CFSE dilution.

Principal Findings

HIV infected individuals had significantly higher frequencies of CD4⁺FOXP3⁺ T cells (median of 8.11%; range 1.33%–26.27%) than healthy controls (median 3.72%; range 1.3–7.5%; P = 0.002), despite having lower absolute counts of CD4⁺FOXP3⁺ T cells. There was a significant positive correlation between the frequency of CD4⁺FOXP3⁺ T cells and viral load (rho = 0.593 P = 0.003) and a significant negative correlation with CD4 count (rho = −0.423 P = 0.044). 48% of our patients had CD4 counts below 200 cells/µl and these patients showed a marked elevation of FOXP3 percentage (median 10% range 4.07%–26.27%). Assessing the mechanism of increased FOXP3 frequency, we found that the high FOXP3 levels noted in HIV infected individuals dropped rapidly in unstimulated culture conditions but could be restimulated by T cell receptor stimulation. This suggests that the high FOXP3 expression in HIV infected patients is likely due to FOXP3 upregulation by individual CD4⁺ T cells following antigenic or other stimulation.

Conclusions/Significance

FOXP3 expression in the CD4⁺ T cell population is a marker of severity of HIV infection and a potential prognostic marker of disease progression.

Increased peripheral blood leukocyte subsets with regulatory phenotype in clinically stable long-term HIV-infected hemophilia patients on HAART may be beneficial and contribute to a decrease in autoimmunity

After initiation of highly-active antiretroviral therapy (HAART), long-term HIV-infected hemophilia patients have been shown to lose autoantibodies against CD4(+) peripheral blood leukocytes (PBL), suggesting that HAART induces autoimmunity-blocking mechanisms. We compared cytokine levels and subpopulations of lymphocytes and dendritic cells (DC) in the blood of 40 long-term HIV(+) patients with those of 13 long-term HIV(-) hemophilia patients; 23 HIV(+) patients had a detectable retroviral load. Cell subsets were determined using flow cytometry and cytokine levels were measured using ELISA. HIV(+) patients showed higher proportions of DC subpopulations with immunostimulatory phenotypes (p < 0.01), CD8(+) PBL (p < 0.001), and IL-2 (p < 0.001) and sIL-2R plasma levels (p = 0.002) than HIV(-) patients. They also exhibited increased proportions of T PBL with immunosuppressive phenotypes such as CD3(+)CD4(+)CD25(+)Foxp3(+) (p = 0.001), and CD3(+)CD8(+)CD28(-)Foxp3(+) PBL (p < 0.001), and a decreased IL-7R expression on CD3(+)CD8(+) PBL (p = 0.001) compared to HIV(-) patients. Frequencies of CD3(+)CD4(+)CD25(+) PBL producing IL-2, IL-4, IL-10, IL-12, and/or IFN-gamma, and of CD3(+)CD4(+)CD28(-) PBL secreting IL-2 and/or IL-4 were lower in HIV(+) than in HIV(-) patients (p <or= 0.02). Proportions of CD4(+) PBL coated with IgG, IgM, and C3d were similar in HIV(+) and HIV(-) patients (p = n.s.). However, the proportion of CD4(+)gp120(+) PBL was higher in HIV(+) patients (p = 0.002), and associated with low CD3(+)CD4(+)CD25(+)Foxp3(+) PBL (p = 0.012). We conclude that long-term HIV-infected hemophilia patients on HAART show an adaptive immune response, presumably against HIV, in the presence of upregulated immunosuppressive T PBL, downregulated cytokine-producing CD4(+) PBL, and downregulated IL-7R expression on CD8(+) PBL. Increased immunoregulatory T PBL might decrease autoimmunity, thereby contributing to immunological reconstitution and stabilization of long-term HIV-infected hemophilia patients on HAART.

CD4+ and CD8+ T cells expressing FoxP3 in HIV-infected patients are phenotypically distinct and influenced by disease severity and antiretroviral therapy

OBJECTIVES

Forkhead box P3 (FoxP3) is critical for the development of CD4 regulatory T (Treg) cells and is a useful marker to identify this population. Recently, expression of FoxP3 was reported in human CD8 T cells from the blood of untreated HIV-infected individuals. We assessed whether FoxP3 expression in CD8 T cells is associated with suppressive potential and/or with HIV-associated immune activation.

METHODS

FoxP3CD8 T cells in non-HIV donors and in untreated and treated HIV-infected patients were identified by flow cytometry, then examined for coexpression of other Treg cell-associated markers [cytotoxic T lymphocyte-associated antigen (CTLA)-4, GITR, and CD45RO], markers of activation [HLA-DR, Ki-67, and programmed death (PD)-1], and markers of senescence (CD57 without CD28).

RESULTS

Similar proportions of FoxP3-expressing CD4 and CD8 T cells coexpressed HLA-DR and Ki-67. However, compared with FoxP3CD4 cells, FoxP3CD8 cells expressed less CTLA-4, CD28, and CD45RO but more PD-1 and CD57. FoxP3-expressing CD4 and CD8 cells from untreated patients exhibited higher expression of HLA-DR, Ki-67, and PD-1 compared with non-HIV donors and treated patients.

CONCLUSIONS

FoxP3CD8 T cells are phenotypically distinct from FoxP3CD4 and FoxP3CD8 T cells. Expression of FoxP3 is associated with cellular activation in both CD4 and CD8 T cells.

Regulatory T cells in the control of host-microorganism interactions (*)

Each microenvironment requires a specific set of regulatory elements that are finely and constantly tuned to maintain local homeostasis. Various populations of regulatory T cells contribute to the maintenance of this equilibrium and establishment of controlled immune responses. In particular, regulatory T cells limit the magnitude of effector responses, which may result in failure to adequately control infection. However, regulatory T cells also help limit collateral tissue damage caused by vigorous antimicrobial immune responses against pathogenic microbes as well as commensals. In this review, we describe various situations in which the balance between regulatory T cells and effector immune functions influence the outcome of host-microorganism coexistence and discuss current hypotheses and points of polemic associated with the origin, target, and antigen specificity of both endogenous and induced regulatory T cells during these interactions.