Suppression of Tumorigenicity 2 (ST2) signaling is required for regulatory T cell control of Graft-vs. Host Disease

Abstract

Abstract How IL-33-mediated signals impact on ST2-expressing regulatory T cell (Treg) expansion and regulatory functions is poorly understood. To establish the importance of direct IL-33 stimulation of Treg for control of alloimmune responses, we utilized a rodent model of graft-vs. host disease (GVHD) where C57BL/6 mice were irradiated and given a BALB/c bone marrow transplant (BMT) along with BALB/c CD4+ CD25+ Treg from st2+/+ or st2−/− mice at a 1:2 ratio with WT BALB/c CD3+ effector T cells. As expected, WT st2+/+ CD4+ CD25+ cells promoted full protection against GVHD with 90% of recipients receiving st2+/+ CD4+ CD25+ free of GVHD at Day 100 post-BMT. However, only 10% of mice that received st2−/− Treg achieved long-term survival (p=0.0017, st2+/+ v. st2−/−). Associated mechanistic studies revealed that Treg frequency was significantly reduced in recipients receiving st2−/− Treg compared to those receiving st2+/+ Treg. To define the signaling patterns IL-33 generates in Treg, fluorescence activated cell sorting was used to obtain ST2− or ST2+ Treg cells from the splenocytes of Foxp3 reporter mice and IL33 activated signaling downstream of ST2 was quantitated by phosphoflow cytometry. This analysis revealed that IL-33 signaling via ST2 on Treg activates both NF-κB and p38 MAPK. Yet, only IL-33-stimulated p38 MAPK, but not NF-kB, signaling was required for ST2+ Treg expansion. Our studies make two important observations regarding how IL-33 stimulation of Treg supports immune regulation. First, we demonstrate that IL-33 activates p38 MAPK to drive selective ST2+ Treg expansion. Second, we show that IL-33-mediated signals are critical to the capacity of Treg to control the alloimmune responses leading to GVHD.