CXCL1 and inflammatory bowel disease: Similar to the previous work showing that NRG1 (a nonspecific ligand that can bind both ErbB3 and ErbB4 and activate any of the ErbBs depending on context) limits cytokine production in monocytes (14, 15), we found that acute NRG4 treatment led to a significant reduction in Tnf, Cxcl1, and Il1b. Though the magnitude of these changes was moderate, a sustained moderate shift in cytokine production from macrophages may contribute to disease development in IBD (48).