A 52-year-old woman presents with 3 months of painful oral erosions and several new flaccid blisters on the trunk that rupture easily, leaving raw, denuded areas. She reports that the lesions are painful rather than itchy. On exam, gentle lateral pressure on perilesional skin causes the epidermis to shear off (positive Nikolsky sign). A lesional skin biopsy and direct immunofluorescence are performed. Which of the following histopathologic/immunopathologic findings is most likely present?

(Assume no infectious organisms are seen on special stains.)