These findings indicate that Secreted Thrombospondin-1 Regulates Macrophage Interleukin-1 Production and Activation through CD47. and caspase-1 mRNAs. These data demonstrate that thrombospondin-1 exerts CD47-dependent and -independent pro-and anti-inflammatory effects on the IL-1 pathway. Therefore, thrombospondin-1 and its receptor CD47 may be useful targets for limiting the pro-inflammatory effects of lipopolysaccharide and for treating endotoxemia. Therapeutics that modulate immune responses have potential applications ranging from enhancing anti-tumor immunity Rabbit polyclonal to AKR1D1 to preventing the excessive inflammatory responses associated with autoimmunity and septic shock1. Therapeutic antibodies that block specific immune inhibitory pathways such as that mediated by PD1 binding to PD-L1 have yielded durable remissions of several cancers2. The interaction between CD47 and its counter-receptor signal regulatory protein- (SIRP) controls another major inhibitory pathway that limits innate and adaptive tumor immunity3,4. Two antibodies that block the interaction of CD47 on tumor cells with SIRP on macrophages have entered Phase 1 human clinical trials (“type”:”clinical-trial”,”attrs”:”text”:”NCT02216409″,”term_id”:”NCT02216409″NCT02216409, “type”:”clinical-trial”,”attrs”:”text”:”NCT02367196″,”term_id”:”NCT02367196″NCT02367196, NCT02488811). These CD47 antibodies enhance phagocytosis of tumor cells by macrophages and promote clearance of human tumor xenografts in mice that express a mutant SIRP capable of binding human CD47 with high affinity3,5,6. To assess the potential utility of CD47-targeted therapeutics in cancer, one must consider additional physiological and pathophysiological functions of CD47 that could result in detrimental side effects7. Based on the known role of CD47 in limiting phagocytic clearance of red blood cells, anemia is one expected side effect and has been observed in primates8,9,10. Mice lacking CD47 are also known to be more susceptible to some microbial pathogens11, and we recently reported increased susceptibility of CD47-deficient mice to in by macrophages was unchanged. This deficit in macrophage recruitment may result from loss of SIRP signaling in macrophages13. In addition to engaging SIRP and SIRP as a counter-receptor, CD47 is high affinity signaling receptor for thrombospondin-1 (TSP1)7,14. TSP1 circulates at low levels in plasma and is expressed by many cell types including innate immune cells in response to injury or stress15,16,17,18. The absence of TSP1 or CD47 confers increased resistance of cells and tissues to a variety of stresses, and TSP1 signaling through CD47 limits cellular responses to stress through regulation of metabolism, protective autophagy, nitric oxide, and c-Myc signaling7,19,20. Previous studies indicate that TSP1 has context-specific pro- and anti-inflammatory functions21,22,23. Endogenous TSP1 enhances the pathogenesis of systemic infections in mice despite enhancing macrophage activation MC-VC-PABC-DNA31 and PMN recruitment24. The presence of TSP1 also exacerbates surgical and non-surgical peritonitis, but in this context, decreases MC-VC-PABC-DNA31 phagocytic killing, thereby increasing bacterial load during infection25. Ligation of the TSP1 receptor CD47 with a synthetic TSP1 peptide or blocking antibody to TSP1, in the presence of Cowan I protein, significantly inhibited dendritic cells maturation and cytokine production, including the amount of secreted IL-12 and TNF26. The complex TSP1 effects on inflammation are consistent with the existence of multiple TSP1 receptors and binding partners (reviewed in27). Macrophages express at least three known TSP1 receptors, and each mediates distinct functions. Binding of the N-terminal domain of TSP1 to 61 integrin promotes M1 macrophage differentiation or recruitment into tumors and enhances phorbol ester-induced superoxide production and target tumor cell killing by macrophages28. Interaction of the central thrombospondin type 1 repeats of TSP1 with the receptor CD36 stimulates macrophage IL-10 expression29 and contributes to activation of TLR4 signaling30. TSP1 binding to CD47 inhibits macrophage release of IL-1231 and may promote macrophage recruitment MC-VC-PABC-DNA31 into injured vascular tissue17. Ligation with a CD47-blocking antibody, in the presence of infectious overcame inhibitory TSP1 signaling that prevented the maturation of immature dendritic cells into mature DCs that produce inflammatory cytokines32. This inhibitory CD47 signal was not affected by knockdown of SIRP. However, treatment of monocytes and dendritic cells with a CD47-binding peptide also induced cell death33. Infiltration of CD68+ macrophages into liver tissue after ischemia/reperfusion injury was similarly reduced in null mice to be reprogrammed into Mac2+ macrophages in the presence of M-CSF was increased35. Based on MC-VC-PABC-DNA31 prior reports that CD47 associates with lipid rafts containing CD1436 and that TSP1 binding dissociates CD47 from its lateral associations.