Photohapten TCSA painting plus UVA irradiation of murine skin augments the expression of MHC class II molecules and CD86 on Langerhans cells

Hapten painting of skin is known to augment the expression of major histocompatibility complex (MHC) class II, CD54, and CD86 on Langerhans cells. We investigated whether painting with 3,3',4',5-tetrachlorosalicylanilide (TCSA), the representative photohapten, and subsequent irradiation with ultraviolet A (UVA) alter the expression of these surface molecules on epidermal Langerhans cells (LC). BALB/c mice were painted with 5 microl of 0.1% TCSA on the earlobes and irradiated with 16 J/cm2 (at 365 nm) of UVA. Epidermal cells were prepared from these earlobes 24 h later, and the levels of MHC class II, CD54, CD80, and CD86 on these cells were analyzed by flow cytometry. As compared with untreated earlobes, the levels of MHC class II and CD86 on LC were markedly augmented and those of CD54 and CD80 were slightly elevated in earlobes treated with TCSA/UVA. Since neither TCSA painting nor UVA exposure alone enhanced the expression, both treatments were essential for enhancement. A dot plot analysis showed the presence of subpopulations of LC expressing MHC class II and CD86 at high levels. The percentage of these highly expressing LC was increased with increasing concentrations of TCSA and doses of UVA up to 1% and 24 J/cm2, respectively. In addition, keratinocyte expression of CD54 was also augmented by TCSA plus UVA. These results suggest that photohaptens, with following UVA exposure, augment the expression of immunologically functional molecules on LC as do ordinary haptens, leading to effective sensitization and elicitation of contact photoallergy.