The RNA-Binding Protein RBM3 Negatively Regulates Group 2 Innate Lymphoid Cells (ILC2s) and Lung Eosinophilia

The role of RNA-binding proteins (RBPs) in the regulation of Group 2 Innate Lymphoid Cell (ILC2) activation and type 2 innate inflammation is completely unknown. Our studies assessing ILC2 transcript levels by RNA-seq identified RNA-binding motif 3 (RBM3) as highly expressed in ILC2s. RNA-seq was performed on FACS sorted Lineage-Thy1.2+ lymphocytes from Alternaria challenged WT mice. WT and rbm3-/- mice were intranasally challenged with Alternaria extract or 10 ng IL-33. Bronchoalveolar lavage (BAL) and lungs were collected and processed for flow cytometry, histology, and ELISA studies. ILC2s were sorted from rbm3-/- and wild-type mice and stimulated in vitro with IL-33 and leukotriene D4. After profiling 207 RBPs through RNA-seq, we observed that RBM3, an RBP known to enhance mRNA stability and translation, is one of the most highly expressed RBPs in ILC2s. In wild-type ILC2s, RBM3 expression was upregulated with Alternaria challenge. In several Alternaria challenge models, rbm3-/- mice exhibited significant increases in lung eosinophils, BAL Th2 cytokines, and airway inflammation compared with WT mice. Further, Th2 cytokine-producing and proliferating (Ki-67+) ILC2s were also increased in rbm3-/- mice over WT mice. Airway challenges with IL-33 in rbm3-/- mice also demonstrated increases in lung eosinophilia, and in vitro stimulated ILC2s sorted from rbm3-/- mice had greater Th2 cytokine production than wild-type ILC2s. Our data suggest that RBM3 negatively regulates ILC2 activation. This is the first report to our knowledge to identify a clear role for a highly expressed RNA-binding protein in ILC2 function.