Mesenchymal stromal cells (MSCs) exhibit beneficial anti-inflammatory effects against Parkinson's disease (PD) via immunomodulatory actions. However, the underlying molecular mechanism remains unclear. This study aimed to investigate the potential neuroprotective effects of MSCs and the possible mechanisms involved by infusing human umbilical cord MSCs (hMSCs) in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mature male C57BL/6 mice. Subsequently, the striatal content of dopamine (DA) and its metabolites, tyrosine hydroxylase (TH)-positive neurons and activated microglia, circulating inflammatory cytokines, gene expression of cytokines, and NOD-like receptor protein 3 (NLRP3) inflammasome molecules were measured using high-performance liquid chromatography, flow cytometry, immunohistochemistry, immunofluorescent staining, and real-time polymerase chain reaction assays, respectively. Infused hMSCs markedly ameliorated the reduction in striatal DA and loss of TH-positive neurons in the substantia nigra of PD mice. The MPTP-induced activation of microglia and increase in tumor necrosis factor-α and interleukin-1β mRNA expression in the striatum were also attenuated by hMSCs. Furthermore, hMSCs completely reversed the elevated pro-inflammatory cytokine levels in the serum and mRNA expression of cytokines in the peripheral organs of PD mice. Moreover, hMSCs significantly inhibited the expression of caspase-1 and NLRP3 of the NLRP3 inflammasome in both the central and peripheral organs at mRNA level. These data suggest that hMSCs protect dopaminergic neurons in PD mice by suppressing both the central and peripheral inflammatory responses, probably by inhibiting the NLRP3 inflammasome. However, the animals in our study only received several MSC infusions, and the effects of infused MSCs over extended periods on the NLRP3 inflammasome need to be investigated in future studies.Copyright © 2022 The Authors. Published by Elsevier Masson SAS.. All rights reserved.