Bronchoalveolar lavage (BAL) could reveal a significant lymphocytosis or an elevated CD4:CD8 ratio (>3.5), but is not sufficient, alone, to provide the specific diagnosis either of sarcoidosis or of any interstitial disease, though it can be helpful to reveal a suggestive pattern of eosinophilic or hypersensitivity pneumonitis and also to exclude tumors or infectious disorders [66,67]. The gene discussed is CD4; the disease is hypersensitivity pneumonitis.