DERMAL MAST-CELLS DETERMINE SUSCEPTIBILITY TO ULTRAVIOLET B-INDUCED SYSTEMIC SUPPRESSION OF CONTACT HYPERSENSITIVITY RESPONSES IN MICE

Different strains of mice have varying susceptibilities to ultraviolet radiation (UV) of wave length 280-320 nm (UVB) for 50% suppression of systemic contact hypersensitivity (CHS) responses. Prevalence of hist amine-staining dermal mast cells in different strains of mice (C57BL/6 J, DBA/2, BALB/c) correlated directly with their susceptibility to UVB -induced systemic immunosuppression. BALB/c mice carrying Uvs1, a majo r locus for susceptibility to UV-induced immunosuppression, contained greater numbers of dermal mast cells than BALB/c mice of the same pare ntal origin. Strains of mice that were differentiated on their suscept ibility to UVB-induced downregulation of systemic CHS responses were s imilar in their susceptibility to histamine-induced immunomodulation. Histamine, but not UVB irradiation. decreased systemic CHS responses i n mast cell-depleted mice (W-f/W-f). Reconstitution of the dorsal skin of W-f/W-f mice with bone marrow-derived mast cell precursors from no nmutant mice rendered the mice susceptible to UVB irradiation for syst emic suppression of CHS responses. UVB irradiation did not suppress de layed type hypersensitivity responses to allogeneic spleen cells in W- f/W-f`mice. In contrast, W irradiation suppressed CHS responses in W-f /W-f mice when hapten was applied to the irradiated site. This study d emonstrates that dermal mast cells are necessary for the induction of systemic suppression of CHS responses by UVB radiation, and suggests t hat mast cell-derived histamine is one component of this WE-induced sy stemic immunosuppression.