Abstract
The nature and phenotype of infiltrating cells in DTH-like reactions elicited in the murine oral mucosa have been examined by routine histological and immunohistochemical procedures. During the first few hours that followed buccal challenge with the contact sensitizer oxazolone, a discrete lymphocytic reaction was disclosed in the oral mucosa of animals previously sensitized at skin sites, but was absent in animals that had been sensitized at buccal sites. The early lymphocytic reaction in the oral mucosa of skin-sensitized animals preceded the emergence of CD11+ polymorphonuclear cells (PMN) which was most prominent 8 h after hapten challenge and invaded the whole thickness of the oral epithelium. The PMN rapidly disappeared by 24 h. In contrast, early PMN infiltration was virtually absent in specimens from animals similarly challenged but that had been sensitized at local buccal sites. Irrespective of site of initial sensitization, inflammatory reactions developed in the oral mucosa, being maximal by 24 h. At that stage, CD11+ macrophages were the predominant cell type. Both CD4 and CD8 T lymphocytes were scattered in both lamina propria and epithelium, and their numbers were raised throughout the time period studied (2-168 h). IL-2 receptor expression was maximal 16 h post-challenge, and was paralleled by increased DNA synthesis in CD4+ and CD8+ cells, as demonstrated by paired immunohistoautoradiography. Focal accumulations of mononuclear cells containing IL-2 producing cells were readily detected as early as 2-3 h following local challenge with hapten in animals primed at skin but not at buccal sites. Maximal IL-2 staining was detected at 24 h irrespective of initial sensitization site. Interferon-gamma-producing cells were detected at 8 h post-challenge and remained increased during the first 24 h. MHC class II expression was detected on few oral mucosa cells during the first 4 h following hapten challenge, being mainly confined to dendritic-like cells. Consistent with increased numbers of macrophages, MHC class II expression was most intense in specimens obtained 8-24 h after hapten challenge. Thereafter, MHC class II expression was still observed in specimens obtained as late as 72 h, but was essentially associated with patches of basal keratinocytes. Taken together, these observations support the notion that the murine oral mucosa can serve as the site of expression of locally or remotely induced DTH reactions, but also indicate that the site of initial sensitization can profoundly affect the cellular composition of inflammatory reactions subsequent to local buccal challenge.