Failure of macrophage activation to induce pulmonary fibrosis in asbestos-exposed guinea-pigs.

Inhalation of asbestos by specific-pathogen-free (SPF) guinea-pigs the macrophages of which were systemically activated with Freund's complete adjuvant and/or M. tuberculosis (Strain H37Ra) induced a diffuse pulmonary mononuclear-cell infiltration of the interstitium and air space. The severity of the reactions to the various insults was dependent on the treatment given. Although there was no histological evidence of increased collagen, there was a diffuse increase in reticulin in animals which were exposed to asbestos and the macrophages of which were activated. However, even in the case where severe pulmonary inflammatory changes occurred complete resolution of the response took place within 1 year. Therefore in this model activation of macrophages does not have a detrimental effect after inhalation of asbestos.