UVA exposure affects UVB and cis-urocanic acid-induced systemic suppression of immune responses in Listeria monocytogenes-infected balb/c mice

Ultraviolet radiation can inhibit immune responses locally as well as syste mically, Such effects have been measured in animals and humans exposed to u ltraviolet B (wavelength 280-315 nm) (UVB) and ultraviolet A (315-400 nm) ( UVA), The precise wavelength dependence is important for the identification of possible molecular targets and for assessments of risk of different art ificial UV sources and solar UV. In such analyses, it is commonly assumed t hat radiation energy from each wavelength contributes to the effect indepen dent of the other wavelengths. Mere we show that this assumption does not h old good. In the present study, it was investigated whether exposure to bro adband UVA or longwave ultraviolet A I (340-400 nm) (UVA 1) prior to the st andard immunosuppressive UVB protocol might modulate the immunosuppressive effects induced by UVB. Preexposure to broadband UVA or longwave UVA 1, 1 d ay prior to the standard immunosuppressive UVB protocol, inhibited the UVB- induced suppression of delayed type hypersensitivity (DTH) to Listeria mono cytogenes significantly, This effect was not associated with restoring the number of interleukin (IL-12)-positive cells in the spleen. Since isomeriza tion of trans-urocanic acid (UCA) into the immunosuppressive cis-UCA isomer plays a crucial role in UVB-induced immunomodulation, in a second set of e xperiments it was investigated whether immunosuppression induced by cis-UCA might also be downregulated by preexposure to UVA, Animals were exposed to broadband UVA or longwave UVA 1 prior to application of an immunosuppressi ve dose of cis- or trans-UCA as a control. Both UVA and UVA 1 appear to inh ibit the cis-UCA-induced systemic immunosuppression (DTH and IL-12) to L, m onocytogenes, These studies clearly show that UVA radiation modulates both UVB and cis-UCA-induced immunomodulation, In general, our studies indicate that bath broadband UVA and longwave UVA 1 could induce modulation of UVB a nd cis-UCA-induced immunomodulation, As sunlight contains both UVA and UVB radiation the balance between these two radiations apparently determines th e net immunomodulatory effect.