D2-40 Expression in Primary Scarring and Nonscarring Alopecia

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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.