Non-Langerhans cell, antigen-presenting T6^-DR⁺ epidermal cells (EC) appear 3 days following broad band ultraviolet radiation exposure of human skin and are responsible for the increased antigen presentation capacity of BC seen 3 days after UV exposure. To determine the UV wavelengths that induce T6^-DR⁺ EC, volar forearm skin of 10 human volunteers was irradiated in vivo with 4 minimal erythema doses (MED) each of pure UVA (mean 482 J cm^-2), UVB (mean 0.390J cm^-2), and UVC (mean 0.397 J cm^-2). The purity of the light sources was as follows: UVB, 98% of the emission was in the UVB range; UVC, 97% of the irradiance was in the UVC range; UVA, 100% of the energy had wavelengths longer than 340 nm. Three days after UV irradiation with 4 MED of each wavelength band, suction blister-derived EC suspensions were prepared from the UV-exposed and unirradiated sites. Percentages of T6⁺DR⁺ Langerhans cells (LC) and T6^-DR⁺ EC were quantitated. Relative to control EC, which contained 2.4 ± 0.3% T6⁺DR⁺ LC, the mean percentage (± SEM) of T6⁺DR⁺ LC contained within UV-exposed EC was significantly decreased as follows: UVB, 0.5 ± 0.2%; UVC, 0.9 ± 0.1%; UVA, 0.5 ± 0.2% (n = 10). T6^-DR⁺ EC, absent in control EC, were induced both by UVB, 5.2 ± 1.7% and UVC; 1.5 ± 0.4%. Despite the use of more than 1200 times greater doses in j cm^-2of UVA than UVB and UVC, UVA was a poor inducer of T6^-DR⁺ EC(0.5 ± 0.2%) and in about half of these individuals, T6^-DR⁺ EC were undetectable.

The UV wavelengths for induction of T6^-DR⁺ EC lies predominantly within the UVB band, but also to a lesser extent within the UVC band. These wavelengths appear to be analogous to both the wavelengths for generation of increases host susceptibility to UV-induced murine tumors and to the wavelengths for UV-induced systemic suppression of contact hypersensitivity. However, our data indicate that UV wavelengths for induction of systemic suppression of contact hypersensitivity in mice. Taken together, these data suggest that the appearance of T6^-DR⁺ EC, but not the disappearance of T6⁺DR⁺ LC, following UV exposure may be related to the induction of such antigen-specific suppressor T cells.