Comparison of sensitizing protocols for ultraviolet B-induced immunosuppression in C3H mice

To compare previously used protocols for ultraviolet (UV)-induced suppression of contact hypersensitivity in mice, and to develop an optimized protocol for C3H mice, the effect of 3 different allergens, varying allergen concentrations in the induction or challenge phase, local and distant sites of allergen application in respect to irradiation site, 2 mouse substrains and 2 different light sources was studied. A concentration of 0.5% of oxazolone (OXA) gave a slightly better contact sensitization than a 1% concentration of trinitrochlorobenzene (TNCB). Titration experiments revealed that for both OXA and TNCB, a 1% sensitization concentration was optimal, while the optimal challenge concentration was 0.5% for OXA and 1% for TNCB. The magnitude of the resulting contact sensitization was not influenced by either the mouse substrain (C3H/HeJ or C3H/HeN) or the site of allergen application (back or belly), but application of fluorescein isothiocyanate to the ears only produced weak sensitization. A standard UVB dose of 1.3 kJ/m2 suppressed TNCB contact sensitivity to a greater extent than that of OXA. A similar degree of UV-induced suppression was obtained with a given UVB dose, irrespective of a 50-fold difference in the concomitant UVA dose. Based on our results, a proper protocol of contact sensitization for UV-induced immunosuppression in C3H mice includes sensitization with 0.5% OXA on either the mouse back or belly, ear challenge with 0.5% OXA and ear swelling reading 24 h after challenge.