In sarcoidosis, BALF often shows lymphocytosis; however, compared with hypersensitivity pneumonitis, the CD4/CD8 ratio tends to be higher, and characteristic imaging findings such as perilymphatic nodules or bilateral hilar lymphadenopathy help differentiate sarcoidosis from hypersensitivity pneumonitis and other interstitial lung diseases. The gene discussed is CD4; the disease is hypersensitivity pneumonitis.