Immunoregulatory function of PIR-A/B+ DCs in the inflammatory responses of dextran sodium sulfate-induced colitis

Background Dendritic cells (DCs) may play an important role in forms of inflammatory bowel disease (IBD), such as Crohn's disease and ulcerative colitis. DCs are generally recognized as initiators of acquired immunity and also serve as regulators of both innate and acquired immunity. We used the animal model of colitis induced by dextran sodium sulfate (DSS), and examined whether DCs prepared from the colon show immunoregulatory roles in the termination of DSS-induced colitis. Methods C57BL/6 mice exposed to DSS for 5 days developed acute colitis. DCs were isolated from the large intestinal lamina propria, and then analyzed for phenotypical, functional, and genetic data. Results Only PIR-A/B-low conventional DCs (cDCs) were detected in the steady state. However, after the treatment of DSS, PIR-A/B-high cDCs appeared and gradually increased from day 5 to day 7, at which time the DSS-induced colitis was terminated. Then, allogeneic mixed leukocyte reaction (MLR) was performed. The stimulatory activity of PIR-A/B-high cDCs obtained on day 7 was very low, and the addition of PIR-A/B-high cDCs suppressed the T cell proliferation in MLR, indicating the immunoregulatory role of PIR-A/B-high cDCs. The immunoregulatory role of PIR-A/B-high cDCs was confirmed by the in vivo transfer experiment, showing their therapeutic effect on DSS-induced colitis. The message level of TGF beta i was significantly higher in PIR-A/B-high cDCs, while that of IFN-gamma was highly upregulated in PIR-A/B-low cDCs, being well in accordance with the fact that PIR-A/B-high cDCs showed a suppressive function against activated T cells. Conclusion PIR-A/B-high cDCs showed a suppressive function against activated T cells by producing inhibitory cytokines.