Comparison of broadband UVB, narrowband UVB, broadband UVA and UVA1 on activation of apoptotic pathways in human peripheral blood mononuclear cells

Background/purpose: Ultraviolet (UV) radiation is an important therapy for immune-mediated cutaneous diseases. Activation of early apoptotic pathways may play a role in the clinical effectiveness. Different UV wavelengths have different efficacy for various diseases, but it remains unclear whether the ability to induce apoptosis differs with respect to the wavelength, and whether they induce apoptosis through the same mechanism. The aim of this study is to analyze the effects of different UV wavelengths that are used clinically on normal human peripheral blood mononuclear cells (PBMCs). Methods: PBMCs were treated with UV-light sources broadband UVB, narrowband UVB, broadband UVA and UVA1. Initiation of apoptosis was assessed by flow cytometry by staining-treated cells for activated caspases. Immunoblots were performed to measure for cleaved caspase-3, -8, -9, cytochrome c, Bcl 2-interacting domain and poly-(ADP ribose) polymerase cleavage. Results: We demonstrate that all the UV radiation sources induced caspase activation in a dose-and time-dependent manner. Components of both the extrinsic and intrinsic pathways of apoptosis were activated by all of the UV wavelengths tested, but differed in the level of energy needed for activation. Conclusion: The greater effectiveness of UVB on initiation of apoptotic pathway suggests that apoptosis may play a role in the clinical efficacy of UVB-responsive inflammatory cutaneous diseases.