A 46-year-old woman presents with insidious onset of shoness of breath, chest pain, and fatigue. Chest X-ray films reveal bilateral pulmonary infiltrates and enlarged hilar lymph nodes. A biopsy of one of these lesions shows non-necrotizing granulomas. Special stains for fungi and mycobacteria are negative. The patient works as a secretary and has no history of occupational exposure to airborne minerals or organic dusts. Which of the following is the MOST likely diagnosis?