Correlation of neutrophil and monocyte derived interleukin-1 receptor antagonist and interleukin-8 with colitis severity in the rabbit

Activated neutrophils and monocytes produce interleukin (IL)-8, a pro-inflammatory chemokine, but also IL-1 receptor antagonist (IL-1ra), which is an anti-inflammatory cytokine. We were interested to see the profiles of IL-8 and IL-1ra in the colonic tissue and in the peripheral blood leukocytes (PBL) during the development of immune complex induced colitis in rabbits. IL-1ra and IL-8 in PBL were measured in 26 rabbits at time 0 h, 24 h, and 48 h after induction of colitis. The colons were removed at 48 h for measuring myeloperoxidase (MPO), ulcer area, IL-1ra and IL-8. Epithelial damage, crypt abscess formation and leukocyte infiltration of the colonic tissue were major features of this colitis model. During the development of colitis, there was an increase in circulating neutrophils and monocytes (P < 0.0001), but not lymphocytes. Likewise, elevated amounts of IL-1ra (P = 0.0001) and IL-8 (P = 0.0219) production by PBL were observed following induction of colitis. Flow cytometry revealed major source of IL-1ra was monocytes, while the main sources of IL-8 were neutrophils and monocytes. There was correlation between MPO and ulcer area (R_s = 0.6327, P < 0.0001). At 24 h, PBL from MPO^High group (n = 11) showed increased IL-1ra (P = 0.027) and IL-8 (P = 0.0128) levels vs MPO^Low group (n = 15). IL-8 production by PBL showed correlation with tissue MPO (R_s = 0.4273, P = 0.0295). The colitis in this model was associated with an increase in circulating monocytes and neutrophils, which released increased amounts of IL-8 and IL-1ra. Further, IL-8 and IL-1ra showed correlation with the severity of colitis. These observations should significantly further understandings on the role of neutrophils and monocytes in the immunopathogenesis of ulcerative colitis.