Photobiomodulation in acute rejection of fetal intestinal grafts: morphological aspects and lymphocyte activation.

Acute rejection remains a significant challenge in organ transplantation. Photobiomodulation (PBM) has demonstrated anti-inflammatory and regenerative properties, suggesting potential benefits in modulating immune responses. This study aimed to evaluate the effects of PBM on fetal intestinal transplantation in mice.​ The study was conducted in two phases. In the first phase, 77 mice were utilized to assess histological outcomes. Fetal intestines from pregnant C57BL/6 mice were transplanted into BALB/c recipients, forming allogeneic groups (ALLO-GTx) with or without PBM (ALLO-GTxPBM), and syngeneic controls (RG). PBM was applied transcutaneous at the graft site immediately post-surgery (660 nm, 40 J/cm², 1.5 J). Grafts were collected on postoperative days 3, 5, and 7 for hematoxylin-eosin staining and evaluated using Aubert's criteria. In the second phase, spleens from 30 transplanted mice were analyzed on day 7 via flow cytometry for lymphocyte activation markers (CD4+, CD8+, CD44, CD69, CD54, CD62L).​ PBM significantly reduced rejection scores on days 5 (3.5 [3-9] vs. 12 [10-13.8]; p = 0.0006) and 7 (p = 0.0096), and enhanced graft development (p = 0.0079). Flow cytometry revealed decreased activation of CD4 + CD44+CD69+ (9.08% to 3.15%) and CD8 + CD44+CD69+ (1.53% to 0.90%) T cells in PBM-treated animals. Additionally, lower expression levels of CD62L + and CD54 were observed, indicating immunomodulatory effects. PBM improved graft viability and mitigated acute rejection in fetal intestinal transplantation in mice. These findings support further investigation into PBM as a therapeutic strategy to modulate immune responses in transplantation.