Program death-1 regulates peripheral T cell tolerance via an anergy-independent mechanism

Program death-1 (PD-1) has been documented to negatively regulate immune responses. However, the cellular and molecular mechanisms for PD-1-mediated immune suppression have not been fully elucidated. In this study, we show that loss of PD-1 does not lead to defective induction of CD4(+) T cell anergy in vitro and in vivo. Rather, the absence of PD-1 inhibits the development of inducible CD4(+)Foxp3(+) regulatory T cells (iTregs) induced by TGF-β in vitro. In support of this finding, PD-1 deficiency impairs the generation of iTregs in vivo and leads to development of severe T cell-transfer-induced colitis. Mechanistically, defective iTreg generation in the absence of PD-1 was attributed to the heightened phosphorylation of Akt. Therefore, we first demonstrate that PD-1 controls peripheral T cell tolerance via an anergy-independent but iTreg-dependent mechanism.     

Role of antigen persistence and dose for CD4+ T-cell exhaustion and recovery

It is currently not understood how some chronic infections exhaust antigen-specific T cells over time and which pathogen components contribute to exhaustion. Here, we dissected the behavior of primed CD4(+) T cells exposed to persistent antigen using an inducible transgenic mouse system that allowed us to control antigen presentation as the only experimental variable, independent of the persistent inflammation and disease progression that complicate infectious models. Moreover, this system restricted antigen presentation to dendritic cells (DCs) and avoided confounding B, CD8(+) T, or innate cell responses. When antigen presentation was extended beyond the expansion phase, primed CD4(+) T cells survived, but exhibited reduced memory functionality in terms of their proliferative capacity and cytokine expression potential. The effect was antigen dose and time dependent, not associated with increased PD-1 expression or reduced calcium influx, but impaired Jun phosphorylation in response to TCR engagement. Upon antigen removal, the cells regained the ability to proliferate, but remained unable to produce high levels of IL-2 and TNF-α. These data show that persistent antigen by itself rapidly induces a dysfunctional state in CD4(+) T cells that is only partially reversible upon antigen removal. These findings have implications for vaccine optimization and for the possible reinvigoration of CD4(+) T cells during chronic infection.     

Modulatory effect of insulin on T cell receptor mediated calcium signaling is blunted in long lasting type 1 diabetes mellitus

Insulin significantly influences Ca(2+) signals evoked by various stimulants. In type 1 recent onset diabetes mellitus the proliferative response of T cells is significantly decreased. The number of clinical trials exploring the role of anti-CD3 monoclonal antibodies (mAb) as a therapeutic agent in recent onset diabetes mellitus type 1 is increasing last years. Therefore, a better understanding of the interplay between T cell receptor (TCR) dependent Ca(2+) increase, and insulin is of vital clinical significance. The aim of the study was to assess the effect of insulin on TCR evoked Ca(2+) responses in T lymphocytes obtained from healthy volunteers and patients suffering from long lasting diabetes mellitus type 1. Analysis was performed with use of the flow cytometer. We demonstrated that T cells ability to mobilize Ca(2+) was significantly reduced in long lasting diabetes mellitus type 1. Ca(2+) decrease achieved by the long term incubation with anti-CD3 mAb in T cells from healthy volunteers was restored by insulin. Strong interrelationship between baseline Ca(2+) level and plateau phase response to TCR stimulation was observed in the cytoplasm of cells pre-incubated with insulin from both healthy subjects and diabetic patients (r = 0.95, p < 0.0001 and r = 0.94, p < 0.0001, respectively). We postulate the existence of the interplay between TCR mediated activation and insulin. The TCR-insulin interplay is blunted in long lasting diabetes mellitus type 1. These observations may have an important implication for future therapeutic options in diabetes.     

Verotoxin A Subunit Protects Lymphocytes and T Cell Lines against X4 HIV Infection in Vitro

Our previous genetic, pharmacological and analogue protection studies identified the glycosphingolipid, Gb₃ (globotriaosylceramide, P^k blood group antigen) as a natural resistance factor for HIV infection. Gb₃ is a B cell marker (CD77), but a fraction of activated peripheral blood mononuclear cells (PBMCs) can also express Gb₃. Activated PBMCs predominantly comprise CD4⁺ T-cells, the primary HIV infection target. Gb₃ is the sole receptor for Escherichia coli verotoxins (VTs, Shiga toxins). VT1 contains a ribosome inactivating A subunit (VT1A) non-covalently associated with five smaller receptor-binding B subunits. The effect of VT on PHA/IL2-activated PBMC HIV susceptibility was determined. Following VT1 (or VT2) PBMC treatment during IL2/PHA activation, the small Gb₃⁺/CD4⁺ T-cell subset was eliminated but, surprisingly, remaining CD4⁺ T-cell HIV-1_IIIB (and HIV-1_Ba-L) susceptibility was significantly reduced. The Gb₃^-Jurkat T-cell line was similarly protected by brief VT exposure prior to HIV-1_IIIB infection. The efficacy of the VT1A subunit alone confirmed receptor independent protection. VT1 showed no binding or obvious Jurkat cell/PBMC effect. Protective VT1 concentrations reduced PBMC (but not Jurkat cell) proliferation by 50%. This may relate to the mechanism of action since HIV replication requires primary T-cell proliferation. Microarray analysis of VT1A-treated PBMCs indicated up regulation of 30 genes. Three of the top four were histone genes, suggesting HIV protection via reduced gene activation. VT blocked HDAC inhibitor enhancement of HIV infection, consistent with a histone-mediated mechanism. We speculate that VT1A may provide a benign approach to reduction of (X4 or R5) HIV cell susceptibility.