Original Article
Mechanisms of Contact Photosensitivity in Mice: I. T Cell Regulation of Contact Photosensitivity to Tetrachlorosalicylanilide under the Genetic Restrictions of the Major Histocompatibility Complex

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Induction, transfer and specificity of contact photosensitivity to 3, 3′, 4′, 5-tetrachlorosalicylanilide (TCSA) were studied in mice. Mice were sensitized by 2 daily abdominal paintings with 1% TCSA plus irradiations with “black lights.” The degree of hypersensitivity was assayed by measuring the increment of ear thickness 24 hr after challenge with 0.1% TCSA plus irradiation with black lights. Long ultraviolet (320–400 nm) but not erythrogenic (280–320 nm) radiation was required for induction and elicitation of the response. The 24-hr ear reaction was not detectable on day 3, peaked on days 5 to 7, and waned thereafter. The histologic picture of a swollen ear at the peak of the reaction showed dense infiltration of mononuclear cells intermingled with polymorphonuclear leukocytes in the dermis. Treatment of immune lymph node cells with anti-Thy-1.2 antiserum and complement abrogated the ability of these cells to transfer the sensitivity to naive recipients. The successful transfer required the identity of the left half of the major histocompatibility complex between the donor of immune lymph node cells and the recipient. T cells concerned with the photosensitivity did not seem to mediate contact sensitivity to TCSA since dichotomy of the reactivity occurred among photosensitized mice on day 7, one group showing contact sensitivity in addition to the photosensitive reaction while the other being photosensitive alone. The photosensitivity was highly specific for TCSA as immune mice neither photocross-reacted nor cross-reacted with 3′,4′,5-trichlorosalicylanilide, 3,4′,5-tribromosalicylanilide, or bithionol. These results provide a definite proof that contact photosensitivity in mice to TCSA is a highly specific, delayed-type hypersensitivity reaction which is effected by distinct T cell subset(s) under genetic restrictions of the major histocompatibility complex. Furthermore, this simple and reliable method to induce delayed-type photosensitive reactions in mice will be a useful strategy for rapid screening of contact photoallergens.

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