Idiopathic pulmonary fibrosis (IPF) is a disease of unknown etiology characterized pathologically by a chronic inflammatory process (alveolitis) that precedes and likely controls the alterations in connective tissue matrix that eventually destroys the normal lung architecture. The mechanisms involved in this process are not known. A complex cell-cell interactive sequence, involving principally neutrophils, lymphocytes, macrophages, fibroblast, and epithelial cells is believed to be responsible.