Ablation of interaction between IL-33 and ST2 + regulatory T cells increases immune cell-mediated hepatitis and activated NK cell liver infiltration Gregory Noel, 1,2,3 * Muhammad Imran Arshad, 1,2,3 * Aveline Filliol, 1,2,3 Valentine Genet, 1,2,3 Michel Rauch, 1,2,3 Catherine Lucas-Clerc, 2,4 Agnès Lehuen, 5 Jean-Philippe Girard, 6 Claire Piquet-Pellorce, 1,2,3 and Michel Samson 1,2,3 1 Institut National de la Santé et de la Recherche Médicale (Inserm), Institut de Recherche Santé Environnement & Travail (IRSET), Rennes, France; 2 Université de Rennes 1, Rennes, France; 3 Structure Fédérative BioSit UMS 3480 CNRS-US18 Inserm, Rennes, France; 4 Service de Biochimie CHU Rennes, Université de Rennes 1; Rennes, France; 5 Inserm UMRS 1016-CNRS UMR 8104, Institut Cochin, Université Paris, Descartes, France; and 6 Institut de Pharmacologie et de Biologie Structurale, Centre National de la Recherche Scientifique (IPBS-CNRS), Université de Toulouse, Toulouse, France Submitted 9 March 2016; accepted in final form 30 May 2016 Noel G, Arshad MI, Filliol A, Genet V, Rauch M, Lucas-Clerc C, Lehuen A, Girard J-P, Piquet-Pellorce C, Samson M. Ablation of interaction between IL-33 and ST2 + regulatory T cells increases immune cell-mediated hepatitis and activated NK cell liver infiltra- tion. Am J Physiol Gastrointest Liver Physiol 311: G313–G323, 2016. First published June 23, 2016; doi:10.1152/ajpgi.00097.2016.—The IL-33/ST2 axis plays a protective role in T-cell-mediated hepatitis, but little is known about the functional impact of endogenous IL-33 on liver immunopathology. We used IL-33-deficient mice to investigate the functional effect of endogenous IL-33 in concanavalin A (Con A)-hepatitis. IL-33 -/- mice displayed more severe Con A liver injury than wild-type (WT) mice, consistent with a hepatoprotective effect of IL-33. The more severe hepatic injury in IL-33 -/- mice was associ- ated with significantly higher levels of TNF- and IL-1 and a larger number of NK cells infiltrating the liver. The expression of Th2 cytokines (IL-4, IL-10) and IL-17 was not significantly varied be- tween WT and IL-33 -/- mice following Con A-hepatitis. The per- centage of CD25 + NK cells was significantly higher in the livers of IL-33 -/- mice than in WT mice in association with upregulated expression of CXCR3 in the liver. Regulatory T cells (Treg cells) strongly infiltrated the liver in both WT and IL-33 -/- mice, but Con A treatment increased their membrane expression of ST2 and CD25 only in WT mice. In vitro, IL-33 had a significant survival effect, increasing the total number of splenocytes, including B cells, CD4 + and CD8 + T cells, and the frequency of ST2 + Treg cells. In conclu- sion, IL-33 acts as a potent immune modulator protecting the liver through activation of ST2 + Treg cells and control of NK cells. concanavalin A-hepatitis; immune cells; liver; interleukin-33-defi- cient mice; ST2 receptor; regulatory T cells INTERLEUKIN-33 (IL-33), a member of the IL-1 family, drives immune responses by interacting with its specific receptor, ST2, and IL-RAcP (1, 39). IL-33 is mostly produced in the nucleus of cells in barrier tissues, such as epithelial and endothelial cells (primarily in the lung, skin, and brain) (29, 39), but it is also produced by hematopoietic cells such as macrophages or mast cells following stimulation in vitro (31). ST2 is produced by various immune cells, including mast cells, granulocytes, dendritic cells, NK/NKT cells, and Th2 lympho- cytes (28), and this receptor has also recently been detected on regulatory T cells (Treg cells) (27). Treg cells form a hetero- geneous population of CD4 + CD25 + Foxp3 + cells. They are involved in both the normal physiological and pathological suppression of immune reactivity. Treg cells play an important role in many diseases, including autoimmune diseases, inflam- matory disorders, transplant rejection, tumorigenesis, and in- fections (41). The role of the IL-33/ST2 axis remains unclear. IL-33 drives innate immune responses in various inflammatory conditions in vivo (30) and has been shown to induce anti-helminth and antiviral responses (10, 35). These findings indicate a role for the IL-33/ST2 axis in mediating adaptive immune responses. Indeed, IL-33 acts as a central mediator, driving Th2 differen- tiation by inducing the production of IL-5 and IL-13 (32, 34). Moreover, IL-33 suppresses protective Th1 differentiation in protozoan infections (36) but promotes Th1 differentiation in a mouse model of viral infection (7, 8). The IL-33/ST2 axis may therefore orchestrate both Th1 and Th2 immune responses, depending on the type of activated cell/tissue involved and the microenvironment and cytokine network in damaged tissues. IL-33 has been implicated in many diseases. It has protective effects against obesity, atherosclerosis, and helminth infection but exacerbates asthma, arthritis, experimental autoimmune encephalomyelitis, and dermatitis (22). Finally, by interacting with ST2 + Treg cells, IL-33 seems to control the immune system in various pathological conditions, including heart transplantation (43), breast cancer growth or metastases (20), and experimental colitis (14, 38). Liver endothelial cells constitutively express IL-33, and we have shown IL-33 to be overexpressed in hepatocytes during necrotic NKT-TRAIL-mediated hepatic cell death (4, 5) and viral hepatitis (2). IL-33 is also produced by the hepatic stellate cells in hepatic fibrosis (26). Thus, during liver inflammation, IL-33 is released after liver cell death (4), and it was consid- ered to act as an “alarmin,” like high-motility group box protein 1 and IL-1 (18). However, the effects of endogenous IL-33 during liver inflammation remain obscure, and the ST2 + liver immune cells and the effects of IL-33 on these target cells have yet to be characterized. In this study, we aimed to decipher the role of endogenous IL-33 and its target immune cell populations during liver inflammation induced by concanavalin A (Con A) in mice. Liver inflammation rapidly leads to the production of copious amounts of IL-33 by hepatocytes and liver endothelial cells (5). The Con A-induced hepatitis model is representative of auto- * G. Noel and M. Arshad contributed equally to this work and shared first coauthorship. Address for reprint requests and other correspondence: M. Samson, INSERM- U1085, IRSET, Université de Rennes 1, 2, Ave. du Professeur Léon Bernard, 35043 RENNES Cedex, France (e-mail: michel.samson@univ-rennes1.fr) Am J Physiol Gastrointest Liver Physiol 311: G313–G323, 2016. First published June 23, 2016; doi:10.1152/ajpgi.00097.2016. 0193-1857/16 Copyright © 2016 the American Physiological Society http://www.ajpgi.org G313 Downloaded from journals.physiology.org/journal/ajpgi (034.228.024.229) on June 16, 2020.