Establishment of murine model of eosinophil-infiltrating drug photoallergy and elucidation of its immunological mechanism

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We established a murine model of the eosinophil-infiltrating type of drug photoallergy by using afloqualone (AQ), a representative photosensitive drug. AKR/J mice were sensitized by an i.p. injection of afloqualone solution and irradiation of shaved abdomen with UVA. This sensitization procedure was repeated 2-12 times (twice a week), and 3 days after the last immunization, mice were challenged by an s.c. injection of AQ solution and irradiation of the same site with UVA. Mice receiving more than 10 times of sensitization exhibited a massive infiltrate of eosinophils and lymphocytes at the challenged site. This reaction was AQ photoantigen-specific, and AKR/J mice were a high responder strain of this sensitivity. The sensitivity was successfully transferred with 5-8x10^7 immune lymph node and spleen cells into naive mice. CD4^+ T cells were responsible for this sensitivity, since 1x10^7 CD4^+ cells alone induced a high level of sensitivity reaction and the addition of other lymphocyte populations did not enhance the reaction. Culture supernatants from immune lymph node cells contained a higher level of IL-4 and a lower level of interferon-g than those from naive mice. Finally, the skin of AQ-photochallenged site exhibited high expression of CCL24/eotaxin-2, a chemokine for eosinophils. It is suggested that eosinophilic drug photoallergy is medated by sensitized Th2 cells and locally produced eosinophil-attracting chemokines. This model is useful for exploring the mechanism of eosinophil-infiltrating photosensitivity.