| Abstract: | Langerhans cells are the only cells within the epidermis that normally express immune response-associated antigens (referred to as Ia in mice and HLA-D in humans). However, in the epidermis of patients with allergic contact dermatitis or individuals undergoing a delayed-type hypersensitivity response, the keratinocytes at the reaction site are induced to express HLA-DR. In this study the inducible expression of Ia by the keratinocytes of mice was found to be directly correlated with the intensity and duration of experimentally induced contact hypersensitivity (CH) responses. During a CH response in animals that were sensitized on the belly and challenged on the ear with the contact-sensitizing (CS) agent oxazolone, the keratinocytes in the challenged, but not the unchallenged, ear were induced to express Ia. In comparison with animals that were sensitized and challenged at different sites, an intensified expression of Ia by the keratinocytes was associated with a twofold increase in ear swelling in mice that were sensitized and challenged with oxazolone at the same site. Curiously, the challenge of oxazolone-sensitized ears with dinitrofluorobenzene (an unrelated CS agent), croton oil (a nonspecific inflammatory agent), or acetone/olive oil (a noninflammatory agent) also induced both a marked keratinocyte expression of Ia and an enhanced CH response. These results suggest that residual antigen at the original sensitization site may be mobilized to function as the challenge stimulus to elicit a CH response, in association with keratinocyte expression of Ia, when CS-sensitized skin is perturbed with a nonspecific agent. Further evidence of an association between CH responsiveness and keratinocyte expression of Ia came from the following observations. First, the magnitude and duration of a CH response was markedly increased in pertussis toxin (PT)-treated mice. These enhanced responses were associated with intense Ia expression by the keratinocytes in the epidermis at the reaction site. Because PT is known to have an adjuvant effect on delayed-type hypersensitivity reactions, as well as to alter the normal regulatory mechanisms associated with this type of response, it is possible that Ia+ keratinocytes play a synergistic role in the enhanced CH responses that are observed in PT-treated animals. Second, a direct correlation between keratinocyte expression of Ia and CH responsiveness was observed in athymic nude mice that were challenged with oxazolone after receiving an adoptive transfer of lymphoid cells from oxazolone-primed normal syngeneic donors.(ABSTRACT TRUNCATED AT 400 WORDS) |
