Equine bone marrow mesenchymal stromal cells inhibit reactive oxygen species production by neutrophils without affecting other important microbicidal functions

Abstract

Abstract Neutrophils (PMN) are the largest leukocyte population in the blood of most mammals including horses, playing an important defensive role in many infectious diseases. However, the mechanisms that increase PMN as one of the main cellular subsets in the defense against pathogens, could also be involved in the pathophysiology of dysregulated inflammatory conditions. Mesenchymal stem/stromal cells (MSCs) are a heterogeneous population with a modulatory potential on the inflammatory response, and are known to interact with nearly all cells of the immune system including PMN. In this study, we investigate the in vitro modulation of equine bone marrow-derived MSCs on phagocytosis, ROS production, and NETs generation from equine PMN. We found that in co-culture with MSCs, unstimulated PMN produces less ROS (2.88% ± 1.43) than PMN in single culture (5.89% ± 2.63); interestingly, co-cultured PMN remains conditioned to produce fewer ROS after PMA stimulation in comparison to PMN not cultured with MSCs. We also found that inhibition of ROS production by co-cultured PMN occurred not only after prolonged PMN-MSC co-incubation (4 hours), but also when MSC were present in the culture at the moment of adding the stimuli (30% less than control), suggesting that MSCs don’t only modulate PMN functions prior to their arrival to the inflammatory site, but also at the inflammatory niche itself. Additionally, we found that incubation with MSC supernatant strongly inhibited ROS production (83% ± 6.35 less than control) without affecting phagocytosis or capacity for NETosis. These results support the potential use of MSCs in equine inflammatory conditions where neutrophils are the main effector inflammatory cells