A patient undergoing chest x-ray following an automobile accident is found to have an enlarged mediastinum with bilateral hilar and right paratracheal adenopathy. The patient has been asymptomatic, but careful examination demonstrates an enlarged cervical lymph node. This node is biopsied and demonstrates involvement by small, non-caseating granulomas. Occasional giant cells with stellate inclusions are seen within the granulomas. These are most likely which of the following?