Exposure of skin to UVB radiation (290-320 nm) modulates the immune system, with most studies showing a suppression of Th1-driven immune responses. This study investigated the effects of UVB on Th2-associated immune responses using a murine model of allergic respiratory inflammation. C57BL/6, histamine receptor-1 knockout (H1RKO), and histamine receptor-2 knockout (H2RKO) mice were exposed to a single 4 kJ/m(2) dose of UVB (twice a minimal edemal dose) on shaved dorsal skin 3 days before intranasal sensitization with papain, a cysteine protease homologue of the dust mite allergen Der p 1. HIRKO mice demonstrated enhanced papain-specific inflammatory responses in the lung-draining lymph nodes (LDLNs), whereas the responses of H2RKO mice closely mimicked those of C57BL/6 mice. UVB irradiation 3 days before sensitization reduced in vitro papain-specific proliferation of LDLN cells of C57BL/6 and HIRKO mice but not H2RKO mice 24 h after challenge. The regulatory effect of UVB was transferred by adoptive transfer of unfractionated LDLN cells from UVB-irradiated, papain-sensitized C57BL/6 and HIRKO donor mice in naive recipients of the corresponding strain that were subsequently sensitized and challenged with papain. Additionally, UVB exposure suppressed papain-induced IL-5 and IL-10 production in vitro by LDLN cells from HIRKO mice but not from C57BL/6 mice or H2RKO mice. The results of this study demonstrate systemic immuno-modulation of responses to intranasally delivered Ag by UVB irradiation and implicate a role for the H2 receptor in UV13-induced suppression of Ag-specific responses in the draining lymph nodes.