Impaired resolution of DSS-induced colitis in mice lacking the glucocorticoid receptor in myeloid cells

Inflammatory bowel disease (IBD) is a highly prevalent intestinal disorder for which no cure exists. Currently, the standard first-line treatment of IBD consists of systemic glucocorticoid (GC) application, even though therapy can be complicated by unresponsiveness or adverse effects. In view of the importance of macrophages and neutrophils for the pathogenesis of IBD we set out to define the relevance of these cell types as targets of GC using the mouse model of DSS-induced colitis. We found that the disease did not resolve in GR(lysM) mice lacking the GC receptor (GR) in myeloid cells after removal of the chemical insult. While clinical symptoms and tissue damage in the colon ameliorated again in GR(flox) mice, the disease further aggravated in GR(lysM) littermates. The observed difference coincided with an increased abundance of macrophages in inflammatory infiltrates in the colon of mutant mice whereas neutrophil and T cell numbers were similar. Concomitantly, systemic IL-6 secretion and mRNA levels of pro-inflammatory cytokines in the colon were elevated in GR(lysM) mice and gene expression of scavenger receptors and IL-10 was diminished. Taken together, our results reveal an important role of myeloid cells as targets of GC in DSS-induced colitis and probably in IBD in humans as well.