(See also Overview of Interstitial Lung Disease and Langerhans Cell Histiocytosis.) Pulmonary Langerhans cell histiocytosis is a disease in which monoclonal CD1a-positive Langerhans cells (a type of histiocyte) infiltrate the bronchioles and alveolar interstitium, accompanied by lymphocytes, plasma cells, neutrophils, and eosinophils.