The matrix metalloproteinases (MMPs) that participate in the extracellular matrix metabolism play a important role in the progression of pulmonary fibrosis. The effects of the MMPs are regulated by several factors including Th-1 cytokines, interferon-γ (IFN-γ). Up to now, IFN-γ is known to inhibit pulmonary fibrosis, but little is known regarding the exact effect of IFN-γ on the regulation of the MMPs.

This study investigated the effects of interferon-γ on the pulmonary fibrosis and the expression of the lung MMP-2,-9, TIMP-1,-2, and Th-2 cytokines in aa rat model of bleomycin induced pulmonary fibrosis.

Male, specific pathogen-free Sprague-Dawley rats were subjected to an intratracheal bleomycin instillation. The rats were randomized to a saline control, a bleomycin treated, and a bleomycin+IFN-γ treated group.

The bleomycin+IFN-γ treated group was subjected to an intramuscular injection of IFN-γ for 14 days. At 3, 7, 14, and 28 days after the bleomycin instillation, the rats were sacrificed and the lungs were harvested. In order to evaluate the effects of the IFN-γ on lung fibrosis and inflammation, the lung hydroxyproline content, inflammation and fibrosis score were measured. Western blotting, zymography and reverse zymography were performed at 3, 7, 14, 28 days after bleomycin instillation in order to evaluate the MMP-2,-9, and TIMP-1,-2 expression level. ELISA was performed to determine the IL-4 and IL-13 level in a lung homogenate.

1. 7 days after bleomycin instillation, inflammatory changes were more severe in the bleomycin+IFN-γ group than the bleomycin group (bleomycin group : bleomycin+IFN-γ group=2.08 ± 0.15 : 2.74 ± 0.29, P<0.05), but 28 days after bleomycin instillation, lung fibrosis was significantly reduced as a result of the IFN-γ treatment (bleomycin group : bleomycin+IFN-γ group=3.94 ± 0.43 : 2.46 ± 0.13, P<0.05).

2. 28 days after bleomycin instillation, the lung hydroxyproline content was significantly reduced as a result of IFN-γ treatment (bleomycin group : bleomycin+IFN-γ group=294.04 ± 31.73 µgram/g : 194.92 ± 15.51 µgram/g, P<0.05).

3. Western blotting showed that the MMP-2 level was increased as a result of the bleomycin instillation and highest in the 14 days after bleomycin instillation.

4. In zymography, the active forms of MMP-2 were significantly increased as a result of the IFN-γ treatment 3 days after the bleomycin instillation, bleomycin+IFN-γ group (bleomycin group : bleomycin+IFN-γ group=209.63 ± 7.60% : 407.66 ± 85.34%, P<0.05), but 14 days after the bleomycin instillation, the active forms of MMP-2 were significantly reduced as a result of the IFN-γ treatment (bleomycin group : bleomycin+IFN-γ group=159.36 ± 20.93% : 97.23 ± 12.50%, P<0.05).

5. The IL-4 levels were lower in the bleomycin and bleomycin+IFN-γ groups but this was not significant, and the IL-13 levels showed no difference between the experiment groups.

The author found that lung inflammation was increased in the early period but the pulmonary fibrosis was inhibited in the late stage as a result of IFN-γ. The inhibition of pulmonary fibrosis by IFN-γ appeared to be associated with the inhibition of MMP-2 activation by IFN-γ.

Further studies on the mechanism of the regulation of MMP-2 activation and the effects of MMP-2 activation on pulmonary fibrosis is warranted in the future.