Untreated PP skin is characterized by strong and diffuse epidermal keratinocyte expression of the aberrant differentiation marker, keratin 17 (K17; a), accompanied by reduced expression of the terminal differentiation marker, loricrin (g). As early as 2 days following a single injection of adalimumab (n=6), there is significant reduction in K17 expression (b) with restoration of strong diffuse loricrin expression (h). By day 7, there is almost complete loss of K17 expression (c) with continued normalization of loricrin expression and orthokeratosis (h). Biopsies on day 28 and 84 revealed near complete healing of PP skin resembling PN skin as depicted (d–f, j–l).