In vivo UC-MSC infusion led to more M2 macrophages in pancreatic islets and therefore alleviated islet dysfunction in T2D mice, and inhibition of IL6 production in MSCs resulted in fewer intraislet M2 macrophages and attenuated islet restoration, indicating that M2 macrophages play an important role in MSC-induced islet restoration. Here, IL6 is linked to type 2 diabetes mellitus.