CD4 and hypersensitivity pneumonitis: Bronchoalveolar lavage (BAL) allows specific cellular findings of the disease to be detected, such as lymphoid polyclonal proliferation, predominantly CD4+ high-intensity T-cells alveolitis, associated with intra-alveolar macrophages and foci of organizing pneumonia, fibrosis and non-necrotizing granulomas; however, surgical lung biopsy is required for definite diagnosis.