D2-40 expression in primary scarring and nonscarring alopecia.

The pathogenesis of scarring alopecia is believed to be related to damage to stem cells within, and outside the confines of, the follicular bulge region. Scattered reports indicate that D2-40, a monoclonal antibody that specifically detects a fixation-resistant epitope on podoplanin, highlights the basal cell layer of the outer root sheath. Given this, we sought to ascertain involvement of the same in a total of 52 cases of alopecia (33 scarring and 19 nonscarring). D2-40 expression, noted in the peripheral layer of the outer root sheath (above and below attachment of the pilar muscle), was similar in 24/33 (73%) and increased in 9/33 (27%) in the infundibular region of cases of scarring alopecia in comparison to its expression in 17/19 (90%; no expression noted in the other 2) of cases of nonscarring alopecia. The absence of a unifying diagnosis in entities demonstrating an increase precludes any correlation from being made regarding D2-40 expression and histologic diagnosis. However, more recently, podoplanin has been shown to be a novel Fos target gene in some skin cancers. Thus, from a scientific perspective, involvement of Fos-dependent transcription mechanisms in the etiopathogenesis of select scarring alopecias does not seem entirely unreasonable although studies defining the role of the Fos-podoplanin axis in development of the normal hair follicle are required before a definitive conclusion can be drawn.