Regulatory T Cells Dynamically Regulate Selectin Ligand Function during Multiple Challenge Contact Hypersensitivity

Abstract

Regulatory T cells (Tregs) play critical roles in restricting T cell–mediated inflammation. In the skin, this is dependent on expression of selectin ligands required for leukocyte rolling in dermal microvessels. However, whether there are differences in the molecules used by Tregs and proinflammatory T cells to undergo rolling in the skin remains unclear. In this study, we used spinning disk confocal microscopy in Foxp3-GFP mice to visualize rolling of endogenous Tregs in dermal postcapillary venules. Tregs underwent consistent but low-frequency rolling interactions under resting and inflamed conditions. At the early stage of the response, Treg adhesion was minimal. However, at the peak of inflammation, Tregs made up 40% of the adherent CD4+ T cell population. In a multiple challenge model of contact hypersensitivity, rolling of Tregs and conventional CD4+ T cells was mostly dependent on overlapping contributions of P- and E-selectin. However, after a second challenge, rolling of Tregs but not conventional CD4+ T cells became P-selectin independent, and Tregs showed reduced capacity to bind P-selectin. Moreover, inhibition of E-selectin at this time point resulted in exacerbation of inflammation. These findings demonstrate that in this multiple challenge model of inflammation, Treg selectin binding capacity and the molecular basis of Treg rolling can be regulated dynamically.

T-lymphocyte homing: an underappreciated yet critical hurdle for successful cancer immunotherapy

“…182,183 Expression of E/P-selectin ligands have also been detected on T regs within inflamed tissues, and might help steer T regs into inflamed tumor sites. 184 Differentiation and expansion of T regs is promoted by TGF-β expressed by tumor or dendritic cells. 185 T regs inhibit immune responses to cancer via multiple mechanisms, including through expression of immunosuppressive IL-10 and/or by reduction of CD4 + and CD8 + T cell proliferation, cytotoxicity, effector functions, and IL-2 production.…”

PSGL-1: A New Player in the Immune Checkpoint Landscape

“…However, it is clear that selectin binding on T cells can be dynamically regulated. For example, in a model of contact sensitivity, Tregs were also found to engage P-selectin on inflamed endothelium via PSGL-1 but this capacity was lost upon subsequent challenge [81]. Although CD4 + and CD8 + T cell effectors acquire selectin binding capacity permitting PSGL-1 engagement and recruitment to inflammatory sites [82], they can then lose glycosylation enzymatic activity as a response resolves, suggesting that inflammatory processes can control selectin-binding by PSGL-1 on T cells (Figure 4B).…”

Viewing immune regulation as it happens: in vivo imaging for investigation of regulatory T‐cell function

“…To understand Treg homing to the periphery in more detail, we used confocal intravital microscopy in a model of skin contact sensitivity to examine the intravascular interactions of Tregs in the dermal microvasculature 27 , 28 . Tregs were observed to undergo constitutive but low frequency rolling in dermal microvessels.…”

“…A subsequent second challenge displayed a further change in the selectin requirement for Treg rolling in that rolling of Tregs, but not T conv , became independent of P‐selectin, relying solely on E‐selectin. This was attributed to a reduction in the capacity of circulating Tregs to bind P‐selectin following a second antigen challenge 28 . The same approach was used to examine Treg adhesion.…”