CX3CR1 and colitis: Since macrophage CX3CR1 plays such an important role in gut tolerance, we also determined its mRNA expression in mouse colon (Fig. 3d) and observed a modest but significant reduction of CX3CR1 expression in Nur77-KO colon lysates, which may indicate a decreased macrophage tolerance possibly making Nur77-KO mice more prone to develop colitis.