Pathogenesis of chronic hypersensitivity pneumonitis (HP) - differences and similarities to idiopathic pulmonary fibrosis (IPF)

Pathogenetically, chronic hypersensitivity pneumonitis (HP) and idiopathic pulmonary fibrosis (IPF) seem to be very different. Chronic HP is considered a complex immunopathological sydrome caused by exposure to a wide variety of organic particles and involving both humoral and cell-mediated immune responses. In contrast, idiopathic pulmonary fibrosis (IPF) is an epithelialfibroblastic disease. The fibrotic response is driven by injured and abnormally activated epithelial cells. On the other hand, both diseases also exhibit several clinical and pathogenetic similarities and the differential diagnostic separation of both entities is a huge challenge. For example, features of the UIP (usual interstitial pneumonia) pattern that characterizes IPF radiologically and histopatholocially, may also be found in patients with chronic HP. Furthermore, immunological prozesses seem to be involved in the pathogenesis not only of chronic HP, but also of IPF. Vice versa, typical pathogenetical elements of IPF like epithelial apoptosis may also be detected in chronic HP. The articel summarizes the differences and similarities between chronic HP and IPF with a particular focus on the pathogenesis.