[The pivotal role of CXCR3 in the pathogenesis of bleomycin-induced pulmonary fibrosis]

Abstract

Objective: To investigate the contribution of chemokine receptor-CXCR3 to the fibrotic disease process induced by bleomycin in CXCR3 gene deficient mice.

Methods: Sixty-two CXCR3 knock-out mice with C57Bl/6 background were established by gene targeting. Forty-eight sex-, age- and weight-matched C57Bl/6 mice were challenged by injection of bleomycin via trachea. Lung tissue was stained with HE and Masson-trichrome methods. Lung hydroxyproline content was evaluated. Bronchoalveolar lavage was performed using PBS, and the cell number and differentials were counted by Diff-Quick staining. TNF-alpha, IL-5 and TGF-beta in the lung homogenate were measured by ELISA. T lymphocytes were analyzed by FACScan. Unpaired t test was explored to compare the difference between two groups.

Results: On day 14 after bleomycin injection, CXCR3 knockout mice were protected from BLM-induced lung injury and fibrosis as evidenced by less inflammatory cells in the lung interstitium and hydroxyproline content in the lung tissue compared to the wild type littermates [3.92 +/- 0.37 vs 5.33 +/- 0.34, P < 0.05; (67.0 +/- 24.2) microg/left lung vs (211.5 +/- 24.2) microg/left lung, P < 0.01]. On day 7 after bleomycin administration, there was less infiltration of neutrophils, lymphocytes and CD(4)(+) T lymphocytes into lung tissue in CXCR3 knockout mice than those in the wild-type mice [(3.25 +/- 0.61) x 10(5) vs (6.13 +/- 0.86) x 10(5), P < 0.05]; [(8.15 +/- 1.96) x 10(5) vs (13.48 +/- 1.47) x 10(5), P < 0.05]; [(9.00 +/- 1.00) x 10(4) vs (15.60 +/- 2.00) x 10(4), P < 0.05]. Lower level of fibrogenic cytokine release, including the altered production of TNF-alpha and IL-5, was seen in CXCR3 knockout mice compared to the wild type mice [(1,023 +/- 113) microg/L vs (1,530 +/- 178) microg/L, P < 0.05; (403 +/- 50) microg/L vs (755 +/- 95) microg/L, P < 0.05] on day 7 postbleomycin injection, whereas TGF-beta level was decreased significantly in CXCR3 knockout mice compared to the wild-type mice on day 14 postbleomycin administration [(2,211 +/- 289) microg/L vs (5,388 +/- 1,071) microg/L, P < 0.05].

Conclusions: These data imply that CXCR3 signaling promotes CD(4)(+) T-cell recruiting and initiates fibrogenic cytokine cascade following intratracheal bleomycin administration and indicate that CXCR3 might be a therapeutic target for pulmonary fibrosis treatment.