Ultraviolet A1 (UVA1) phototherapy implications for systemic sclerosis still remain area of research. The wide spectral waveband of UVA1 could react with many chromophores in the skin, leading to different effects of the immune system. 1 In accordance with the physical properties of UVA1 and the optical features of the skin, the narrowband UVA1 would influence collagen metabolism with a reduced chance of side effects. None of the previously conducted studies evaluated the effectiveness of

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... band UVA1 on dermal fibrosis. Objectives: The main objective of the present study was to define the impact of high-dose of 365±5 nm UVA1 on the dermal thickness in pre-established, bleomycin-induced mouse model of scleroderma. Methods: Forty two DBA/2 line mice were randomly divided into the following 6 groups (7 animals in each): group I-mice injected with sodium chloride (NaCl) for 3 weeks; group IImice injected with bleomycin (Bleo) for 3 weeks; group IIImice injected with NaCl for 8 weeks; group IVmice injected with Bleo for 3 weeks and then with NaCl for 5 weeks; group Vmice injected with Bleo for 8 weeks; group VImice injected with Bleo for 8 weeks and parallel treated with average cumulative dose of 1200 J/cm 2 of UVA1 for the last 5 weeks (the treatment group). Light source emitting a narrow band UVA1 of 365±5 nm and 21 mW/cm 2 ; power density was used in the study. Histological analysis was performed for the evaluation of dermal thickness. The Mann -Whitney U test was used for statistical analysis. Results: After bleomycin injections that spanned a period of 3 and 8 weeks, the dermal thicknesses were significantly (p=0.002) higher (group II -433.69 ±54.37 mm and group V -497.43±57.83 mm, respectively) as compared to that of the healthy controls (group I -166.04±25.29 mm and group III -178.18 ±42.35 mm, respectively). The 3 weeks of bleomycin injections and the following 5 weeks of NaCl did not cause any spontaneous regression of dermal fibrosis (group IV -443.87±41.77 mm; group II -433.69±54.38 mm; p=0.482). Dermal thickness in mice injected with bleomycin for 8 weeks and irradiated with UVA1 for the last 5 weeks was significantly lower than that in mice challenged only with bleomycin for 8 weeks (group VI -253.96±31.83 mm and group V -497.43 ±57.83 mm, respectively; p=0.002). Furthermore, treatment with 1200 J/cm 2 of UVA1 in parallel with profibrotic stimulus of bleomycin resulted in a lower dermal thickness as compared with pre-existing fibrotic changes in the group IV observed after 3 weeks of bleomycin injections (group VI -253.96±31.83 mm and group IV -443.87±41.77 mm; p=0.002) (figure 1). Abstract AB0186 - Figure 1