The expression of MHC class II (Ia) antigens on mouse keratinocytes following epicutaneous application of contact sensitizers and irritants.

The expression of MHC class II (Ia) antigens on mouse keratinocytes was studied following both the induction and elicitation of contact sensitivity, and after primary irritant reactions. IA+ and IE+ keratinocytes were detected, using an indirect immunofluorescence assay on epidermal sheets, only after the induction and elicitation of contact sensitivity with the sensitizers oxazalone, picryl chloride and 2,4-dinitrochlorobenzene but not with formaldehyde. Ia+ keratinocytes were not detected after epicutaneous application of the non-sensitizing irritants croton oil, SDS and anthralin, or following attempted sensitization of nude mice, suggesting that the expression of Ia antigen on keratinocytes during contact sensitivity reactions is T-cell mediated. Because Ia antigen expression on keratinocytes could be detected only several days after induction or elicitation of contact sensitivity, and contact sensitization could also be demonstrated to occur independently of aberrant Ia expression, Ia+ keratinocytes cannot be involved in the initiation of these reactions. However, they might be important in exerting an immunomodulatory influence during the later stages of the responses to certain sensitizers.