Abstract
The factor XIIIa‐positive (FXIIIa+) cell is a potent antigen‐presenting cell, which has been described as increasing in numbers in various chronic inflammatory conditions. The purpose of this study was to investigate the distribution and frequency of FXIIIa+ cells in acute recurrent aphthous ulcer (RAU) lesions compared with induced traumatic ulcer (TU) lesions and with clinically healthy oral mucosa. Samples were labeled with polyclonal rabbit anti‐human FXIIIa antibodies in avidin‐biotin‐peroxidase complex (ABC) staining. Most of the FXIIIa‐immunoreactive cells in TUs and normal mucosa were spindle‐shaped, whereas a relatively large, dendritic‐like cell was predominant in RAU lesions. FXIIIa+ cells were quite frequent within mononuclear cell‐rich inflammatory cell infiltrates and in perivascular areas in RAU lesions. In contrast, FXIIIa+ cells were not found in mucosal epithelium or in the neutrophil‐rich areas. RAU mononuclear cell‐rich inflammatory cell infiltrates appeared to have greater numbers of positively stained cells than the TU‐inflammatory cell infiltrates (199±67 vs 110±31 cells/mm2p < 0.001). Overall, FXIIIa+ dendrocytes were increased in numbers, and apparently also in size, in RAU lesions (274±68/mm2) as compared lo controls (177±74/mm2, p < 0.01), and to TU lesions (183±50 mm2, P < 0.01). Interestingly, relatively high numbers of FXIIIa+ dendrocytes were also found in deep connective tissue in RAU sections compared with TUs (281 ±80 vs 166±57, p < 0.01). The characteristic changes in the size and shape of individual FXIIIa+ cells, their typical distribution and increase in frequency in RAU lesions indicate active involvement in the local pathogenic mechanisms. Localization to perivascular areas/inflammatory cell infiltrates would be compatible with a role in antigen presentation.