Probiotic strain <i>Bacillus subtilis</i> TO-A modulates the formation of neutrophil extracellular traps

Neutrophil extracellular traps (NETs) have important innate immune functions that prevent pathogenic infections. In the intestinal tract, NET formation contributes to the prevention of the systemic spread of commensal bacteria associated with mucosal barrier dysfunction, and exacerbates inflammation in various chronic enteritis conditions. Therefore, NETs in the intestinal tract are bilateral and appropriate control methods based on the host's condition are required. In this study, we found that the probiotic bacterial strain Bacillus subtilis TO-A (BSTOA), used in both human and veterinary medicine, modulates NET formation in a bidirectional manner. Co-culture of neutrophil-like HL-60 (nHL-60) cells with BSTOA at a low ratio of 0.1:1 (BSTOA:nHL-60 cells) promoted subsequent NET formation. Conversely, co-culture of nHL-60 cells with BSTOA at a high ratio of 10:1 suppressed NET formation. Furthermore, transcriptome analysis demonstrated that BSTOA affects cellular processes through pathways such as peptidyl-prolyl isomerization, regulation of cyclin-dependent protein serine/threonine kinase activity, and chromatin remodeling to exert its function in nHL-60 cells. This is the first report of a single bacterial strain with the ability to regulate NET formation in a bidirectional manner, suggesting that BSTOA has potential utility as a preventive or therapeutic agent for NET-related diseases.