CD4+CD25+ Regulatory T Cells Can Mediate Suppressor Function in the Absence of Transforming Growth Factor β1 Production and Responsiveness

Abstract

CD4+CD25+ regulatory T cells inhibit organ-specific autoimmune diseases induced by CD4+CD25−T cells and are potent suppressors of T cell activation in vitro. Their mechanism of suppression remains unknown, but most in vitro studies suggest that it is cell contact–dependent and cytokine independent. The role of TGF-β1 in CD4+CD25+ suppressor function remains unclear. While most studies have failed to reverse suppression with anti–transforming growth factor (TGF)-β1 in vitro, one recent study has reported that CD4+CD25+ T cells express cell surface TGF-β1 and that suppression can be completely abrogated by high concentrations of anti–TGF-β suggesting that cell-associated TGF-β1 was the primary effector of CD4+CD25+-mediated suppression. Here, we have reevaluated the role of TGF-β1 in CD4+CD25+-mediated suppression. Neutralization of TGF-β1 with either monoclonal antibody (mAb) or soluble TGF-βRII-Fc did not reverse in vitro suppression mediated by resting or activated CD4+CD25+ T cells. Responder T cells from Smad3−/− or dominant-negative TGF-β type RII transgenic (DNRIITg) mice, that are both unresponsive to TGF-β1–induced growth arrest, were as susceptible to CD4+CD25+-mediated suppression as T cells from wild-type mice. Furthermore, CD4+CD25+ T cells from neonatal TGF-β1−/− mice were as suppressive as CD4+CD25+ from TGF-β1+/+ mice. Collectively, these results demonstrate that CD4+CD25+ suppressor function can occur independently of TGF-β1.

TGF‐β regulates pathology but not tissue CD8+ T cell dysfunction during experimental Trypanosoma cruzi infection

“…One source of TGF-b is regulatory T cells (Tregs), and while the exact relationship between Tregs and TGF-b is still unclear [22,23], there is a large body of data demonstrating that Tregs exert their regulatory effects at least in part through TGF-b [24][25][26][27][28]. Our recent studies failed to define a role for regulatory T cells in regulating CD8 + T cell function in muscle of T. cruzi-infected mice as determined by depletion (or functional inactivation [29]) of Tregs using PC61 anti-CD25 Ab [30].…”

TGF‐β1 production by CD4+CD25+ regulatory T cells is not essential for suppression of intestinal inflammation

“…Although CD4 + CD25 + T cells from Smad3 -/-mice appeared to function as efficiently as WT CD4 + CD25 + T cells in our colitis model, it remains possible that TGF-b could play a stimulatory role in the induction of CD4 + CD25 + suppressor activity, perhaps in a Smad3-independent fashion [16].…”

“…Thus, it is possible that the very slight increase in intestinal inflammation observed in groups receiving TGF-b1 -/-compared to WT Treg cells is not exclusively due to contaminating effector T cells, but instead result at least in part from a lack of TGF-b1 signaling in Treg cells and consequential fading of CD4 + CD25 + Treg cell function over time. Although CD4 + CD25 + T cells from Smad3 -/-mice appeared to function as efficiently as WT CD4 + CD25 + T cells in our colitis model, it remains possible that TGF-b could play a stimulatory role in the induction of CD4 + CD25 + suppressor activity, perhaps in a Smad3-independent fashion [16].To assess CD4 + CD25 + Treg cell function in TGF-b1 -/-mice, it is essential to isolate these cells from neonatal asymptomatic mice, as TGF-b1 -/-animals develop a multi-organ autoimmune phenotype by 3-5 wk of age [11,12]. In this study, TGF-b1 -/-CD4 + CD25 + T cells from 3-to 10-day-old neonatal mice were functionally comparable to WT mice, and the expression of activation markers on total CD4 + CD25 + T cells from these two strains was comparable (data not shown), confirming our previous observation [16].…”

Intravenous apoptotic spleen cell infusion induces a TGF-β-dependent regulatory T-cell expansion

“…Membrane TGF neutralization with mAb is indeed not easy to perform. 7 Human and murine Treg generated in the periphery from naive CD25 À CD4 þ T cells can exert suppression trough a cell-tocell contact-dependent and cytokine-independent mecha nism. [45][46][47] Such findings suggest that apoptotic cell-induced Treg that exert cell-to-cell suppression are generated peripherally from CD4 þ T cells in the presence of TGF-b.…”

“…4 Thus, CD4 þ CD25 þ Treg cells have been shown to prevent acute graft-versus-host disease (GvHD), 5,6 a frequent complication of allogeneic hematopoietic cell (HC) transplantation. Expression of CD25 is shared by different CD4 þ Treg subsets including CD4 þ CD25 þ 'suppressive' T cells, which act by cell contact-dependent mechanisms, 3,7 IL-10-producing T regulatory type 1 (Tr1) cells 8 and TGF-b-producing Th3 cells. 9 Other Treg-associated molecules such as CD62L or CTLA-4 (CD152) are commonly used to identify CD4 þ Treg cells.…”