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The murine buccal mucosa is an inductive site for priming class I‐restricted CD8+ effector T cells in vivo

The present study shows that Langerhans cells of the buccal mucosa and the skin share a similar phenotype, including in situ expression of MHC class II, the mannose receptor DEC‐205 and CD11c, and absence of the costimulatory molecules B7.1, B7.2 and CD40 as well as Fas. Application of 2,4‐dinitrofluorobenzene (DNFB) onto the buccal mucosa is associated with a rapid migration of dendritic cells (DC) to the epithelium and induction of B7.2 expression on some DC. Buccal sensitization with DNFB elicited a specific contact sensitivity (CS) in response to skin challenge, mediated by class I‐restricted CD8+ effector T cells and down‐regulated by class II‐restricted CD4+ T cells, demonstrated by the lack of priming of class I‐deficient mice and the enhanced response of class II‐deficient mice, respectively. CS induced by buccal immunization is associated with priming of class I‐restricted CD8+ effector T cells endowed with hapten‐specific cytotoxic activity. Thus, the buccal epithelium is an inductive site, equivalent to the epidermis, for the generation of CS independent of CD4 help, and of cytotoxic T lymphocyte (CTL) responses mediated by class I‐restricted CD8+ T cells. We propose that immunization through the buccal mucosa, which allows antigen presentation by epithelial DC efficient for priming systemic class I‐restricted CD8+ CTL, may be a valuable approach for single‐dose mucosal vaccination with subunit vaccines.