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Knockout Mice*
* From the Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, MD.
Correspondence to: Edward S. Chen, MD, Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, 5501 Hopkins Bayview Circle, Baltimore, MD 21224
(CHEST 2001; 120:8S)
Since
mouse strains susceptible to bleomycin, such as C57BL/6J, tend to
produce T-helper 1 cytokines in response to immune activation, we
hypothesized that the inflammatory response to bleomycin is mediated,
in part, by local production of the T-helper 1 cytokine, interferon
(IFN)-
. We determined that IFN-
is expressed in BAL fluid 12 to
24 h following bleomycin exposure in bleomycin-susceptible
C57BL/6J and A/J mice (p < 0.05) but not bleomycin-resistant BALB/c
mice. The early expression of IFN-
was associated with increased
lung inflammation, weight loss, and mortality 10 days following 5 U/kg
of intratracheal bleomycin instillation in C57BL/6J and A/J mice
compared with BALB/c mice or control mice receiving saline solution.
The T-helper 2 cytokine, interleukin-4, was either not detected or
detected at minimal levels in BAL fluid from mice in all groups. To
directly determine a role for IFN-
in mediating the inflammatory or
fibrotic response to bleomycin, C57BL/6J mice with a homozygous null
mutation of the IFN-
gene (IFN-[/]) and wild-type C57BL/6J
mice were exposed to either 5 U/kg or 1.5 U/kg of bleomycin or saline
solution. IFN-
(-/-) mice demonstrated significantly lower
parenchymal inflammation (p < 0.05) and mortality (p < 0.0001)
following 5 U/kg of intratracheal bleomycin instillation compared with
C57BL/6J control mice. At 10 days following bleomycin administration,
there was no difference in total lung collagen as determined by
hydroxyproline assay. Since the lack of difference in collagen content
at 10 days could reflect insufficient time for any potential
differences in the fibrotic processes to be manifest, we evaluated mice
at 3 weeks following exposure to lower doses of bleomycin that would
produce less mortality. At 3 weeks following lower-dose 1.5 U/kg of
intratracheal bleomycin treatment, IFN-
(-/-) mice demonstrated
significantly lower parenchymal inflammation (p < 0.05), mortality
(p < 0.05), weight loss (p < 0.005), and total lung
hydroxyproline content (p < 0.005) compared with control C57BL/6J
mice. Together, these results suggest that IFN-
mediates, in part,
bleomycin-induced pulmonary inflammation and fibrosis. The effects of
locally produced IFN-
may potentiate the toxicity associated with
bleomycin exposure that results in enhanced pulmonary fibrosis
following increased lung
injury.
Footnotes
Abbreviation: IFN = interferon
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