IL-12p40(-/-) mice treated with intratracheal bleomycin exhibit decreased pulmonary inflammation and increased fibrosis.

Pulmonary lymphohistiocytic inflammation and fibrosis characterize bleomycin (BLM) lung injury. IL-12, a p70 cytokine produced primarily by macrophages and dendritic cells, promotes T-helper-1-mediated inflammation. IL-12 production by blood monocytes and bronchoalveolar large mononuclear cells (BAMC) was investigated at Days 1-14 following intratracheal administration of BLM. In the lung, BAMC showed a large peak of IL-12 expression at Day 5 that returned rapidly toward baseline. IL-12p40(-/-) mice treated with BLM intratracheally showed less pulmonary mononuclear cell inflammation at Day 7 than wild-type controls, whereas pulmonary fibrosis and hydroxyproline content were increased in IL-12p40(-/-) mice at Day 14. The expression of IP-10, RANTES, and eotaxin were decreased in IL-12p40(-/-) mice and lung IL-6 expression was increased, all compared to controls. We conclude that IL-12 promotes the lymphohistiocytic response to BLM and may inhibit the late development of pulmonary fibrosis. Copyright 2002 Elsevier Science.