Role of repeated lung injury and genetic background in bleomycin-induced fibrosis

Am J Respir Cell Mol Biol. 2003 Sep;29(3 Pt 1):375-80. doi: 10.1165/rcmb.2003-0029OC. Epub 2003 Apr 3.


Current hypotheses of the pathogenesis of many forms of pulmonary fibrosis suggest that (i) a stimulus results in repeated or prolonged episodes of lung injury, and (ii) genetic factors modulate the outcome of the injury. The commonly employed single-exposure bleomycin model results in only temporary fibrosis. Therefore, we evaluated whether repeated bleomycin exposures, in the setting of a genetic background more likely to develop a T helper 2 (Th2) response, would induce prolonged fibrosis. Lung fibrosis was induced by intratracheal bleomycin injection, either as a single exposure or as three consecutive exposures. We found that bleomycin induced a Th2-like environment in both Th1-biased C57BL/6J and Th2-biased DBA/2 mice. We also found histologic changes and collagen increases consistent with lung injury/fibrosis at early time points, but prolonged fibrosis only after multiple exposures in the Th2-biased DBA/2 mice. We also determined if impaired healing of bleomycin-induced injury would prolong fibrosis in the C57BL/6J mice. Endothelial nitric oxide (which protects endothelial cells from oxidant-induced injury) synthase knockout animals on a C57BL/6J background also had prolonged fibrosis, similar to DBA/2 mice, after multiple bleomycin exposures. This was specific to eNOS, as inducible nitric oxide synthase knockout animals cleared the fibrosis as effectively as wild-type C57BL/6J mice. This data indicate that healing of injury/fibrosis after bleomycin is complex and can be determined by a number of genetic and environmental factors.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Antimetabolites, Antineoplastic / pharmacology
  • Bleomycin / metabolism
  • Bleomycin / pharmacology*
  • Collagen / metabolism
  • Fibrosis / chemically induced*
  • Fibrosis / genetics*
  • Interferon-gamma / metabolism
  • Interleukin-13 / biosynthesis
  • Lung / metabolism
  • Lung / pathology
  • Lung Injury*
  • Mice
  • Mice, Inbred BALB C
  • Mice, Inbred C57BL
  • Mice, Inbred DBA
  • Mice, Knockout
  • Nitric Oxide Synthase / genetics
  • Nitric Oxide Synthase / metabolism
  • Nitric Oxide Synthase Type II
  • Nitric Oxide Synthase Type III
  • RNA / metabolism
  • RNA, Messenger / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Th2 Cells
  • Time Factors


  • Antimetabolites, Antineoplastic
  • Interleukin-13
  • RNA, Messenger
  • Bleomycin
  • RNA
  • Interferon-gamma
  • Collagen
  • Nitric Oxide Synthase
  • Nitric Oxide Synthase Type II
  • Nitric Oxide Synthase Type III
  • Nos2 protein, mouse
  • Nos3 protein, mouse