Objective:To investigate the effect and regulation of umbilical cord-derived mesenchymal stem cells (UC-MSCs) on islets function and NOD-like receptor family, pyrin domain containing 3 (NLRP3) and autophagy in type 2 diabetic mellitus (T2DM) mice.Methods:Experimental study. Twenty, 8-week-old, male C57BL/6J mice were selected and divided into a normal control group ( n=5) and a high-fat feeding modeling group ( n=15). The model of T2DM was established by high-fat feeding combined with intraperitoneal injection of low-dose streptozotocin. After successful modeling, those mice were divided into a diabetes group ( n=7) and a UC-MSCs treatment group ( n=7). The UC-MSCs treatment group was given UC-MSCs (1×10 6/0.2 ml phosphate buffer solution) by tail vein infusion once a week for a total of 4 weeks; the diabetes group was injected with the same amount of normal saline, and the normal control group was not treated. One week after the treatment, mice underwent intraperitoneal glucose tolerance tests and intraperitoneal insulin tolerance tests, and then the mice were sacrificed to obtain pancreatic tissue to detect the expressions of interleukin-1β (IL-1β) and pancreatic and duodenal homeobox 1 (PDX-1) by immunofluorescence. The bone marrow-derived macrophages were stimulated with lipopolysaccharide and adenosine triphosphate (experimental group) in vitro, then co-cultured with UC-MSCs for 24 h (treatment group). After the culture, enzyme-linked immunosorbent assay was used to detect the secretion level of IL-1β in the supernatant, and immunofluorescence staining was used to detect the expression of NLRP3 inflammasome, and related autophagy proteins. Statistical analysis was performed using unpaired one-way analysis of variance, repeated measure analysis of variance. Results:In vivo experiments showed that compared with the diabetes group, the UC-MSCs treatment group partially repaired islet structure, improved glucose tolerance and insulin sensitivity (all P<0.05), and the expression of PDX-1 increased and IL-1β decreased in islets under confocal microscopy. In vitro experiments showed that compared with the experimental group, the level of IL-1β secreted by macrophages in the treatment group was decreased [(85.9±74.6) pg/ml vs. (883.4±446.2) pg/ml, P=0.001], the expression of NLRP3 inflammasome and autophagy-related protein P62 was decreased, and the expressions of microtubule-associated protein 1 light chain 3β (LC3) and autophagy effector Beclin-1 were increased under confocal microscopy. Conclusions:UC-MSCs can reduce the level of pancreatic inflammation in T2DM mice, preserving pancreatic function. This might be associated with the ability of UC-MSCs to inhibit the activity of NLRP3 inflammasomes in macrophages and enhance autophagy levels.