Splenic erythroid progenitors decrease TNF-α production by macrophages and reduce systemic inflammation in a mouse...

In inflammatory bowel disease (IBD), inflammation can occur beyond the intestine and spread systemically causing complications such as arthritis, cachexia, and anemia. Here, we determine the impact of CD45, a pan-leukocyte marker and tyrosine phosphatase, on IBD. Using a mouse model of T cell transfer colitis, CD25^- CD45RB^high CD4⁺ T cells were transferred into Rag1-deficient mice (RAGKO) and CD45-deficient RAGKO mice (CD45RAGKO). Weight loss and systemic wasting syndrome were delayed in CD45RAGKO mice compared to RAGKO mice, despite equivalent inflammation in the colon. CD45RAGKO mice had reduced serum levels of TNF-α, and reduced TNF-α production by splenic myeloid cells. CD45RAGKO mice also had increased numbers of erythroid progenitors in the spleen, which had previously been shown to be immunosuppressive. Adoptive transfer of these erythroid progenitors into RAGKO mice reduced their weight loss and TNF-α expression by splenic red pulp macrophages. In vitro, erythroid cells suppressed TNF-α expression in red pulp macrophages in a phagocytosis-dependent manner. These findings show a novel role for erythroid progenitors in suppressing the pro-inflammatory function of splenic macrophages and cachexia associated with IBD.