A 13-year-old girl has two non-tender lesions on her fingers that have appeared over the past 5 months. On physical examination, there are 0.5-cm slightly raised, pebbly-surfaced, gray-white papules, one on the dorsum of her distal right index finger, and another periungual to her little finger. They gradually disappear over the next 18 months. Which of the following is the most likely factor in the pathogenesis of her lesions?

Verrucae, or warts, are quite common, particularly in children, and tend to persist for up to a couple of years. There are subtypes of human papillomavirus (HPV) associated with distinct clinical appearances: verruca vulgaris on the hands, verruca plana (flat wart) on the face and hands, verruca palmaris on the palms, verruca plantaris on the soles, and condyloma acuminatum (venereal wart) on genitalia. BRAF mutations can be present with melanocytic proliferations, such as dysplastic nevi. IgA deposition is found with dermatitis herpetiformis. Contact dermatitis is a form of type IV hypersensitivity. Photosensitive dermatitis may be seen with niacin deficiency.