A 17-year-old woman is brought to the physician by her parents because "she has been acting strangely" for a couple of days. Over the past 3 months, she has experienced malaise, joint pain, weight loss, and sporadic fever. The patient appears agitated, with a temperature of 38degC (101degF). Other physical findings include malar rash, erythematous-pink plaques with telangiectatic vessels, oral ulcers, and nonblanching purpuric papules on her legs. Laboratory studies show elevated levels of BUN and creatinine. The anti-double-stranded DNA antibody test is positive. Biopsy of sun-damaged lesional skin would most likely show which of the following histopathologic findings in this patient?