The “Type 2” Cytokine, Interlukin-33, Generates Potent CD4 + ST2 + Tbet + Th1 Responses Independently of IL-12 under Lymphopenic Conditions

Abstract

Introduction: The stromal-derived cytokine interleukin (IL)-33 is described as a promoter of CD4+ T helper type 2 (Th2) and regulatory T cells (Treg) responses. Yet, recipient conditioning before allogeneic hematopoietic cell transplantation (alloHCT) releases IL-33 to promote type 1 alloimmunity and graft-versus-host disease (GVHD). Conditioning causes lymphopenia and releases self and bacteria materials that promote myeloid cell secretion of IL-12, a type 1 immune response driver. IL-12 drives T cell expression of Tbet, which induces the IL-33 receptor, ST2, on T cells. While it is known that IL-33-mediated GVHD immunopathology involves direct stimulation of donor T cells, −the precise mechanisms mediating IL-33 support of GVHD are unclear. Herein we tested the hypothesis that neutralizing IL-12 post alloHCT would block IL-33-support of CD4+ T helper type 1 (Th1) response and limit GVHD by favoring Th2 or Treg responses. Methods: B6 Rag2−/−γc−/− mice were used to test the impact of IL-33 on CD4+ T cells in lymphopenic condition. These mice were infused with 5x104 CD90.1+CD4+ST2+Treg and 4.5x105 CD90.2+CD4+Foxp3−CD44loST2lo T cells and recieved PBS or IL-33 on day (d)1-8. Splenocytes were assessed by flow cytometry on d9. To establish the role of IL-12 in IL-33-mediated GVHD responses, irradiated BALB/c recipients were given 1x107 B6 alloHCT with 2x106 B6 T cells. Some cohorts also received IL-12p40 neutralizing Ab or control Ab alone, or with IL-33 (d3-7). Survival was determined. Splenocytes from additional mice were assessed at d7. Results: Therapeutic doses of anti-IL-12p40 did not rescue mice from IL-33-mediated acceleration of GVHD (Fig. 1A). Post-alloHCT, IL-33 worked with IL-12 to expand ST2+Tbet+ Th1 cells (Fig. 1B). Surprisingly, only neutralization of IL-12, but not delivery of IL-33, increased Gata-3+ Th2 cells (Fig. 1C) or Treg. During lymphopenia, proliferating Foxp3−CD4+ T cells display ST2 and IL-33 favored the expansion of these non-Treg cells over ST2+ Treg (Fig 2).FigureConclusion: We provide insights into how IL-33 contributes to GVHD. Specifically, donor CD4+ T cells transferred into the lymphopenic environments rapidly upregulate ST2 and are expanded by IL-33. Our data also suggest that after alloHCT, IL-33 does not provide faciliate ST2+ Treg- or ST2+Gata-3+ Th2 expansion, but works with IL-12 to supports a ST2+Tbet+ Th1 responses. This work was supported by funding from the NIH (R21AI12198: HRT).Figure