Alarmins, sequestered self-molecules containing damage-associated molecular patterns, are released during tissue injury to drive innate immune cell pro-inflammatory responses. Whether endogenous negative regulators controlling early immune responses are also released at the site of injury is poorly understood. Herein, we establish that the stromal cell-derived alarmin interleukin-33 (IL-33) is a local factor that directly restricts the pro-inflammatory capacity of graft infiltrating macrophages early after transplantation. By assessing heart transplant recipient samples and using a mouse heart transplant model, we establish that IL-33 is upregulated in allografts to limit chronic rejection. Mouse cardiac transplants lacking IL-33 displayed dramatically accelerated vascular occlusion and subsequent fibrosis, which was not due to altered systemic immune responses. Instead, a lack of graft IL-33 caused local augmentation of pro-inflammatory iNOS+ macrophages that accelerated graft loss. IL-33 facilitated a metabolic program in macrophages associated with reparative and regulatory functions, and local delivery of IL-33 prevented the chronic rejection of IL-33-deficient cardiac transplants. Therefore, IL-33 represents a novel regulatory alarmin in transplantation that limits chronic rejection by restraining the local activation of pro-inflammatory macrophages. The local delivery of IL-33 in extracellular matrix based-based materials may be a promising biologic for chronic rejection prophylaxis.
Tengfang Li, Zhongqiang Zhang, Joseph Guido Bartolacci, Gaelen K. Dwyer, Quan Liu, Lisa Mathews, Murugesan Velayutham, Anna Roessing, Yoojin C. Lee, Helong Dai, Sruti Shiva, Martin H. Oberbarnscheidt, Jenna L. Dziki, Steven J. Mullett, Stacy G. Wendell, James D. Wilkinson, .Steven A Webber, Michelle A. Wood-Trageser, Simon C. Watkins, Anthony J. Demetris, George S. Hussey, Stephen F. Badylak, Heth R. Turnquist