Thrombospondin-1, CD47, and SIRPa display cell-specific molecular signaturesin human islets and pancreata

Thrombospondin-1 (TSP1) is a secreted protein minimally expressed in health but increased in disease and age. TSP1 binds tothe cell membrane receptor CD47, which itself engages signal regulatory protein a (SIRPa), and the latter creates a checkpointfor immune activation. Individuals with cancer administered checkpoint-blocking molecules developed insulin-dependent diabe-tes. Relevant to this, CD47 blocking antibodies and SIRPa fusion proteins are in clinical trials. We characterized the molecularsignature of TSP1, CD47, and SIRPa in human islets and pancreata. Fresh islets and pancreatic tissue from nondiabetic individu-als were obtained. The expression of THBS1, CD47, and SIRPA was determined using single-cell mRNA sequencing, immunofluo-rescence microscopy, Western blot, and flow cytometry. Islets were exposed to diabetes-affiliated inflammatory cytokines andchanges in protein expression were determined. CD47 mRNA was expressed in all islet cell types. THBS1 mRNA was restrictedprimarily to endothelial and mesenchymal cells, whereas SIRPA mRNA was found mostly in macrophages. Immunofluorescencestaining showed CD47 protein expressed by b cells and present in the exocrine pancreas. TSP1 and SIRPa proteins were notseen in islets or the exocrine pancreas. Western blot and flow cytometry confirmed immunofluorescent expression patterns.Importantly, human islets produced substantial quantities of secreted TSP1. Human pancreatic exocrine and endocrine tissueexpressed CD47, whereas fresh islets displayed cell surface CD47 and secreted TSP1 at baseline and in inflammation. Thesefindings suggest unexpected effects on islets from agents that intersect TSP1-CD47-SIRPa