Bronchoalveolar Lavage in Hypersensitivity Pneumonitis: A Series of 139 Patients

Hypersensitivity pneumonitis (HP) is characterized by a lymphocytic alveolitis, classically delineated by an increase of CD8+ lymphocytes, with an inversion of the CD4+/CD8+ ratio. The aim of this study is both to describe the yield and cell bronchoalveolar lavage (BAL) profile and to revisit the assumption of low BAL CD4/CD8 ratio in the diagnosis of HP. A multicentric study was conducted on 139 patients who fulfilled the standardized diagnostic criteria of HP, mainly affected by farmer's lung. Mean total cell count in BAL fluid was 594 ± 401.103 cells /ml. Prominent absolute lymphocytic alveolitis, moderate neutrophilia, and mild eosinophilia and mastocytosis were found. Mean CD4/CD8 ratio was 3.8 ± 6.1 (median 2.1). Thirty four percent of the patients showed lymphocytic CD8 alveolitis (ratio<1). The CD4/CD8 ratio was not different between forms, etiologies of HP, and time elapsed since last antigen exposure, but was higher in women (p=0.02). BAL in HP shows high total cell and lymphocyte counts, moderate neutrophilia, and mild eosinophilia and mastocytosis. An absence of low CD4/CD8 ratio should not at all exclude diagnosis.