Plasmacytoid dendritic cells in alopecia areata: missing link?

BACKGROUND

Type I interferon (IFN) signature has been implicated in alopecia areata (AA). However, type I IFN source has never been documented. Plasmacytoid dendritic cells (PDCs) are generally known to be the main source and most potent producers of local type I IFNs. Their role in AA pathogenesis has never been investigated.

OBJECTIVE

Investigate PDC role in AA.

METHODS

Nineteen AA cases were retrieved from our database and were immunohistochemically tested for PDC occurrence and activity using anti-BDCA-2 and anti-MxA antibodies respectively. Comparison to 10 trichotillomania and 7 androgenetic alopecia (AGA) cases was also done.

RESULTS

Plasmacytoid dendritic cells were present in all AA cases in a peri-bulbar location and, as indirectly assessed by MxA expression, were in an active state producing type I IFNs. All trichotillomania cases showed the presence of PDCs, though significantly less abundant and in a different distribution (mainly superficial perivascular) than that in AA. PDC presence and MxA expression were absent in AGA.

CONCLUSIONS

Plasmacytoid dendritic cells constitute a central component of the peribulbar infiltrate in AA suggesting a significant role in AA pathogenesis. Additionally, PDC distribution could help in microscopically differentiating AA from trichotillomania or AGA.