Hypothesis of classification of pulmonary fibroses.

A new framework for pulmonary fibroses may be obtained by distinguishing the "true" forms (solely collagen hyperplasia) from the "false" forms or mesenchymal fibril lung diseases (collagen, reticular and elastic hyperplasia with neo-angiogenesis): the "true fibroses" are then divisible into those not causing architectural subversion of the lung and those which bring it about. Pulmonary architectural subversion is common to true granulomatous fibroses and mesenchymal fibril lung diseases: it is, in our opinion, the product of a combination of factors, including the hyperactivity of a fibroblast sub-population normally in the minority, stimulated by T lymphocytes which are activated by an autoimmune response to type I collagen produced in excess.