The role of mast cells in non-ablative laser resurfacing with 1,320 nm neodymium:yttrium-aluminium-garnet laser

The aim of this study was to investigate the role of mast cells in mechanisms of collagen remodelling induced by non-ablative laser treatment. The dorsal skin of Kunming (KM) mice was exposed to 1,320 nm neodymium-yttrium-aluminium garnet (Nd:YAG) laser weekly for four consecutive weeks. Biopsies were taken 1 h after irradiation and 1 day, 7 days, 14 days, 30 days and 60 days after the first treatment. Skin samples were studied for mast cells, fibroblasts, and type I and III collagen, by toluidine blue, haematoxylin-eosin (HE) and immunohistochemical staining, respectively. The total number of mast cells in the skin of experimental group was significantly greater than that in the control at 1 h, 1 day, 21 days and 60 days after the first treatment (P < 0.05, respectively). At any of the time points studied, the number of degranulated mast cells in the experimental group was significantly higher than in the control (P < 0.01, P < 0.01, P < 0.05, P < 0.01, P < 0.05, P < 0.05, respectively).The number of fibroblasts in the experimental group exhibited a significant increase in comparison with those in control skin at days 7, 21, 30 and 60 after irradiation (P < 0.05, P < 0.01, P < 0.01, P < 0.05, respectively). The amount of type I collagen was significantly higher than in the control from day 21 to day 60 (P < 0.05, P < 0.01, P < 0.01, respectively), and type III collagen showed a marked increase between day 7 and day 60, compared with the control (P < 0.01, P < 0.05, P < 0.01, P < 0.01, respectively). There was a significant positive correlation between the number of fibroblasts and granulated mast cells (r = 0.549, P < 0.01). The amount of type I and III collagen also showed significant positive correlations with the number of degranulated mast cells (r = 0.555, P < 0.01 and r = 0.579, P < 0.01, respectively). The results suggested that dermal mast cells might be involved in the inflammatory response, fibroblast proliferation and collagen remodelling induced by non-ablative laser treatment.