Retinoids strongly and selectively correlate with keratin 13 and not keratin 19 expression in cutaneous warts of renal transplant recipients

Objective: To compare the expression of keratin (K) 13 and K19 in cutaneous warts of renal transplant recipients (RTRs) and immunocompetent individuals (ICIs). Design: Retrospective, nonrandomized immunohistochemical study. Patients and Methods: Specimens from cutaneous warts of RTRs and ICIs were retrieved from the archives of the Department of Pathology, University Medical Center St Radboud, Nijmegen, the Netherlands. Twenty-one warts from RTRs and 21 from ICIs were examined. Nine RTRs (10 specimens) received either systemic acitretin or topical all-traps retinoic acid, and their effect on both keratins was assessed. Main Outcome Measures: Frequency and expression patterns of K13 and K19 in warts of RTRs vs ICIs and the effect of retinoids. Results: A significantly higher percentage of warts of RTRs expressed K13 compared with warts of ICIs (86% vs 14%, 18 vs 3 cases, respectively; P<.001). In warts of RTRs, retinoid treatment correlated significantly with a particularly strong, segmental K13 expression pattern, which we termed zebroid. Without use of retinoids, K13 was mostly restricted to suprabasal single cells. Keratin 19 was absent in all warts of both patient groups. Conclusions: Retinoids strongly correlate with K13 in a characteristic zebroid pattern in warts of RTRs, making K13 a sensitive marker for retinoid bioactivity in skin (lesions) of RTRs. In non-retinoid-treated RTRs, K13 is also frequently found in warts but without the dramatic zebroid pattern noted in retinoid-treated warts.