Relationship among circulating leukocytes, platelets, and microvascular responses during induction of chronic colitis

The mechanisms by which microvascular alterations contribute to the pathogenesis of the inflammatory bowel diseases (IBDs; Crohn's disease, ulcerative colitis) have not been clearly delineated. The purpose of the current study was to characterize the inflammatory events, microvascular alterations, and blood cell changes that occur in a mouse model of IBD. In this model, CD4+ T-lymphocytes obtained from interleukin-10-deficient mice were injected intraperitoneally into lymphopenic, recombinase-activating gene-1 deficient (RAG−/−) mice. Two groups of control mice were also included: RAG−/− mice and C57BL/6 mice that were injected with phosphate-buffered saline but did not receive the T-cells. Four weeks later, the RAG−/− mice that had received the T-cell transfer showed significant signs of colonic inflammation, but without significant decreases in either body weight or mean arterial blood pressure. T-cell transfer increased the volume % of circulating platelets, while decreasing the number of circulating red blood cells. Additionally, the T-cell transfer tended to increase the circulating numbers of both lymphocytes and neutrophils when compared to unmanipulated RAG−/− mice. First-order colonic arterioles and venules tended to dilate in the colitic mice; however, the dilation was considerably more substantial with higher numbers of circulating leukocytes. The possibility that circulating inflammatory cells initiate the microvascular alterations in colitis warrants further investigation.