Figure 8

Mesenchymal stem cells release nitric oxide after infection with M. tuberculosis and inhibition of NO increases viability of intracellular organisms. BM-MSCs or human THP-1 macrophages were infected with Mtb (MOI = 1) and tested for the release of oxidants by using DCFDA (5-(and-6)-Carboxy-2′, 7′-Dichlorofluorescein Diacetate) for the detection of reactive oxygen species (ROS) and DAF2-DA (Diaminoflurescein diacetate) for nitric oxide with a fluorometer in three similar experiments. (a) MSCs secreted limited levels of ROS with or without infection. (b) Mtb infected MSCs secreted elevated levels of NO compared with similarly infected THP-1 macrophages (**p < 0.05, t test). (c) MSCs were incubated in 100 µM N (G)-monomethyl-L-arginine (L-NMMA) after infection with Mtb, and cell lysates were plated for CFUs over time. Blockade of NO synthesis enhanced intracellular survival of Mtb (**p < 0.009, t test).