A 30-year-old woman suffers a tonic-clonic seizure and presents with delirium and hydrophobia. The patient states that she was bitten on the hand by a bat about 1 month ago. The patient subsequently dies of respiratory failure. Viral paicles are found throughout the brainstem and cerebellum at autopsy. In addition to direct viral cytotoxicity, the necrosis of virally infected neurons in this patient was mediated primarily by which of the following mechanisms?