Photobiomodulation Triggers M1/M2 Macrophage Polarization in Zymosan-Induced Acute Arthritis in Mice.

OBJECTIVE

To investigate whether photobiomodulation (PBM) modulates macrophage polarization in zymosan-induced acute joint inflammation, promoting an M1 to M2 phenotype shift.

METHODS

Mice received intra-articular zymosan and PBM (830 nm, 10 mW) at 3 and 30 J/cm2. Euthanasia occurred at 24, 48, and 72 h. Polarization was assessed via mRNA levels and protein expression.

RESULTS

At 24 h, both fluences downregulated iNOS and Arg-1 mRNA. The 30 J/cm2 dose sustained steady-state mRNA levels through 72 h. Immunohistochemistry showed that 3 J/cm2 reduced M1 cells at 24 h, while 30 J/cm2 was more effective in promoting M2 polarization at 48 and 72 h. Predominance of M2 over M1 macrophages was observed in all treated groups.

CONCLUSION

PBM may modulate acute joint inflammation by driving a phenotypic switch from M1 to M2 macrophages. These regulatory effects depend on irradiation conditions, with higher fluence (30 J/cm2) sustaining a durable pro-resolutive cellular profile.