Introduction: We previously found that mesenchymal stem cells (MSCs) injected intravenously could attenuate
peritoneal adhesion by secreting tumor necrosis alpha-stimulating gene (TSG)-6, while MSCs injected
intraperitoneally could not. However, the underlying mechanism remains unclear. This study was designed to
investigate the means by which MSCs exert their effects.
Methods: Rat bone marrow-derived MSCs/red fluorescent protein (RFP) were injected either intraperitoneally or
intravenously into Sprague-Dawley (SD) rats at different time points after peritoneal scraping. Peritoneal adhesions
were evaluated macroscopically at day 14 after scraping. The distribution of MSCs injected intraperitoneally or
intravenously was traced by two-photon fluorescence confocal imaging and immunofluorescence microscopy. The
co-localization of MSCs and macrophages in the lung and the spleen, and the expression of TSG-6 in MSCs
trapped in the lung or the spleen were evaluated by immunofluorescence microscopy. The concentration of TSG-6
in serum was evaluated by ELISA. After intravenous injection of TSG-6- small interfering (si) RNA-MSCs, the
expression of TSG-6 in MSCs and the concentration of TSG-6 in serum were reevaluated, and peritoneal adhesions
were evaluated macroscopically and histologically.
Results: MSCs injected intraperitoneally failed to reduce peritoneal adhesion, and MSCs injected intravenously
markedly improved peritoneal adhesion. Two-photon fluorescence confocal imaging showed that MSCs injected
intravenously accumulated mainly in the lung, where they remained for seven days, and immunofluorescence
microscopy showed few MSCs phagocytosed by macrophages. In contrast, large numbers of MSCs accumulated in the
spleen with obvious phagocytosis by macrophages even at 4 hours after intraperitoneal injection. Immunofluorescence
microscopy showed that MSCs that accumulated in the lung after intravenous injection could express TSG-6 within 12
hours, but TSG-6-siRNA-MSCs or MSCs accumulated in the spleen after intraperitoneal injection did not. ELISA showed
that the concentration of TSG-6 in serum was increased at 4 hours after intravenous injection of MSCs, while there was
no increase after injection of TSG-6-siRNA-MSCs or after intraperitoneal injection of MSCs. Moreover, intravenous
injection of TSG-6-siRNA-MSCs failed to attenuate peritoneal adhesion.