Figure 5.

Human islets secrete soluble TSP1 and express cell surface CD47, which is maintained under inflammatory stress. Human islets (500 IEQ) from donors without diabetes (n = 4, Hu 1229, Hu 1236, Hu 1237, and Hu 1238) were incubated in islet culture medium with or without IL-1β (50 U/mL), IFN-γ (1,000 U/mL), and TNF-α (1,000 U/mL) for 24 h. Islet lysates were prepared, protein separated by gel electrophoresis and expression of CD47, TSP1, SIRPα, and PD-L1 characterized by Western blot. Representative Western blot showing protein expression (A). Densitometry analysis of expression relative to β-actin (B). Conditioned medium from freshly gathered human islets at baseline and following exposure to inflammatory cytokines for 24 h (n = 4 four donor preparations) was assayed for secreted soluble TSP1 (C). Each dot represents one donor. Significance was determined using paired t test. ns, P >0.05, ***P < 0.001. SIRPα, signal regulatory protein α; TSP1, thrombospondin-1.