Light stimuli attenuates inflammatory activation in primary bone marrow-derived macrophages

Abstract Bone repair depends on a regulated macrophage-driven inflammatory response. Non-activated macrophages (M0) differentiate into pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes in response to microenvironmental signals. This study evaluated, in vitro, the effects of photobiomodulation (PBM) on bone marrow-derived macrophage polarisation. Monocytes were isolated, differentiated into macrophages (M0), and induced to acquire M1- or M2-associated characteristics. Cells were irradiated using a PBM protocol for bone regeneration (equivalent dose of 2.1 E). Cells were analysed according to morphology, expression of M1 ( iNOS , Tnf-α ) or M2 markers ( Arg1 , Cd206 ), protein expression (iNOS and ARG1), and nitric oxide (NO) and reactive oxygen species (ROS) production. Data were analysed using 1-way analysis of variance or Student’s t -test ( p ≤ 0.05). PBM promoted selective and transient modulation of inflammatory and metabolic markers in M0, M1, and M2 macrophages. Compared to non-PBM-treated cells, M1 PBM cells had reduced NO levels, increased early ROS levels, and decreased gene and protein expression. In M2 PBM cells, transient changes in NO and ROS production were detected, with reduced Cd206 expression and similar Arg1 expression, although increased ARG1 protein expression was detected compared to non-irradiated controls. In M0 PBM cells, NO levels remained unchanged, while early ROS levels increased, accompanied by reduced iNos and Arg-1 , and increased Cd206 expression. Under the selected parameters, PBM modulated macrophage inflammatory behaviour, but was insufficient to induce classical macrophage polarisation towards a specific phenotype. These findings suggest that modulation of macrophage-mediated inflammatory responses may contribute to the effects of this PBM protocol during bone repair. Graphical abstract Illustrations were generated using the Illustrae AI-assisted illustration platform.