Recruitment of dendritic cells in oral lichen planus.

Using immunohistochemistry the presence of different dendritic cell (DC) subsets was
analysed in 16 biopsies from patients with oral lichen planus (OLP). A significant increase
of CD1a+/Langerin+ Langerhans cells, DC-SIGN+ DC and CD123+/BDCA2+ plasmacytoid
DCs (PDCs) was found in the epithelium and in the stroma of OLP biopsies compared to
normal oral mucosa. A proportion of DCs were mature DC-LAMP+ and expressed S100
or CD11c, typically found in the interdigitating DCs of nodal T-cell areas. Double staining
revealed that mature DCs co-expressed CCR7, thus indicating the development of a nodal
migratory phenotype upon maturation. Significant recruitment of PDCs producing IFN-α
was demonstrated by the expression of MxA within the lichenoid inflammatory infiltrate and
close cell-to-cell contacts between PDCs and mature DCs were observed, with a significant
correlation between the numbers of these two populations. Moreover, PDCs were also
found to contain Granzyme-B, an associated-cytotoxic granule protein, inducing target cell
apoptosis. Taken together, these results suggest that PDCs may promote maturation of DCs
and amplify the cytotoxicity of lymphoid cells. Finally, the recruitment of different subtypes
of DC, such as Langerhans cells, stromal DC-SIGN+ DCs and PDCs, associated with a
significant proportion of mature DCs, acquiring a CCR7+ ‘migratory’ phenotype, indicate
that they may play a pivotal role in the development of the lichenoid inflammatory infiltrate
that occurs typically in OLP.