Background: Bone marrow mesenchymal stem cells (BM-MSCs), as multipotent cells with self-renewal and plastic-adherent properties, have immunomodulatory effects on immune cells, including neutrophils. These cells are in close proximity in bone marrow (BM) sinusoids with non-multiplicative immature neutrophils. BM-MSCs exert their immunomodulatory effects on adjacent cells both directly (cell-to-cell contact) and indirectly (secretion of soluble factors) . Objectives: The aim of this study was to evaluate the effect of equine bone marrow mesenchymal stem cells (BM-MSCs) on the expression of some pro- and anti-apoptotic genes (p53, survivin and Bcl2) in neutrophils co-cultured with BM-MSCs. Methods: For this purpose, peripheral blood neutrophils were isolated and separately co-cultured for 12 hours with both BM-MSCs and the BM-MSCs΄ supernatant. Four groups were included: neutrophils with only culture media (as control), neutrophils co-cultured with BM-MScs, neutrophils cultured with BM-MSCs’supernatant and neutrophils cultured with lipopolysaccharide (LPS, as positive control). Then, the expression of mentioned genes (p53, survivin and Bcl2) was evaluated by quantitative polymerase chain reaction (qPCR). Results: Compared with control neutrophils, in neutrophils co-cultured with both BM-MSCs and BM-MSCs’ supernatant the mRNA expression levels of p53, as pro-apoptotic gene, and survivin and Bcl2, as anti-apoptotic genes, were remarkably increased and decreased (P<0.05), respectively. Conclusions: These data revealed the notion that the direct contact of BM-MSCs is not obligatory for their effects on the apoptotic status of neutrophils and they affect neutrophils via soluble secreted factors, which is promising for clinical implications in equine medicine.

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