Factor XIIIa-positive dendrocytes are increased in number and size in recurrent aphthous ulcers (RAU).

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/mm2, P < 0.001). Overall, FXIIIa+ dendrocytes were increased in numbers, and apparently also in size, in RAU lesions (274 +/- 68/mm2) as compared to 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. [ABSTRACT FROM AUTHOR]