Abstract
BACKGROUND: Ulcerative colitis, an inflammatory bowel disease, is associated with the massive infiltration of neutrophils. Although the initial infiltration of neutrophils is beneficial for killing bacteria, it is presumed that persistent infiltration causes tissue damage by releasing antibacterial products as well as inflammatory cytokines. A murine C-type lectin receptor, dendritic cell immunoreceptor 1 (Dcir1), is expressed on CD11b(+) myeloid cells, such as macrophages, dendritic cells and neutrophils. It was reported that Dcir1 is required to maintain homeostasis of the immune system to prevent autoimmunity, but it is also involved in the development of infectious disease resulting in the enhanced severity of cerebral malaria. However, the role of Dcir1 in intestinal immune responses during colitis remains unclear. In this study, we investigated the role of Dcir1 in intestinal inflammation using an experimental colitis model induced with dextran sodium sulfate (DSS). RESULTS: In contrast to wild type (WT) mice, Dcir1 (-/-) mice exhibited mild body weight loss during the course of DSS colitis accompanied by reduced colonic inflammation. Dcir1 deficiency caused a reduced accumulation of neutrophils in the inflamed colon on day 5 of DSS colitis compared with WT mice. Consistently, the production of a neutrophil-attracting chemokine, MIP-2, was also decreased in the Dcir1 (-/-) colon compared with the WT colon on day 5. There were fewer myeloperoxidase-positive neutrophils in the inflamed colon of Dcir1 (-/-) mice than in that of WT mice. Moreover, bone marrow neutrophils from Dcir1 (-/-) mice produced less reactive oxygen species (ROS) by lipopolysaccharide stimulation than those from WT mice. This suggests that Dcir1 deficiency decreases the accumulation of tissue destructive neutrophils during DSS colitis. CONCLUSION: Dcir1 enhances the pathogenesis of DSS colitis by altering neutrophil recruitment and their functions.