TNF and acute respiratory distress syndrome: In line with these findings, further studies revealed that the stimulation of MSCs with different insults and inflammatory cytokines, including lipopolysaccharide (LPS), tumor necrosis factor alpha (TNF-α), IL-1β, interferon gamma (IFN-γ), and serum from ARDS patients can induce the secretion of a variety of anti-inflammatory mediators, such as TNF-stimulating gene 6 protein (TSG-6), prostaglandin E2 (PGE2), indoleamine 2,3-dioxygenase (IDO), IL-10, and IL-1 receptor antagonist (IL-1ra) [39, 42–44].