K16 expression in uninvolved psoriatic skin: a possible marker of pre‐clinical psoriasis

Background: K16, a type I keratin, is upregulated in hyperproliferative states including psoriasis. It has been used as a marker of psoriasis and its expression is upregulated in relapsing psoriasis and downregulating in resolving. We evaluated non‐lesional psoriatic skin for K16 expression. Methods: Sixty‐seven non‐lesional and lesional skin samples from patients with psoriasis and normal skin from 19 non‐psoriatic patients were studied by immunohistochemistry on frozen sections with K16. Results: Seventeen of 19 normal skin samples showed staining of basal cells in the deeper part of the rete ridges. Sixty‐two non‐lesional psoriatic skin samples showed intense basal staining of K16. Of the remaining five non‐lesional samples, diffuse intense suprabasal staining in one, pan‐epidermal staining in two, and no staining was seen in two samples. Suprabasal (37), diffuse (14), sandwich (12), and basal (3) pattern staining were seen in psoriatic skin. One psoriatic skin sample did not show any expression. Conclusion: Our results demonstrate that K16 expression is also observed in non‐lesional psoriatic skin and may serve as a marker of preclinical psoriasis.