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Exacerbation of Established Pulmonary Fibrosis in a Murine Model by Gammaherpesvirus

¹ Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, ² Division of Infectious Diseases, Department of Pediatrics and Communicable Diseases, and ³ Immunology Graduate Program, University of Michigan, Ann Arbor, Michigan; ⁴ Veterans Affairs Medical Center, Ann Arbor, Michigan; and ⁵ Department of Microbiology, University of Colorado School of Medicine, Aurora, Colorado

Correspondence and requests for reprints should be addressed to Galen B. Toews, M.D., 6301 MSRB III, 1150 W. Medical Center Drive, Ann Arbor, MI 48109-5642. E-mail: gtoews{at}umich.edu

Rationale: Idiopathic pulmonary fibrosis is a progressive disease with high mortality. Although most patients have a slow, progressive course, some patients will have an acute deterioration in function or acute exacerbation, which carries a poor prognosis. In some cases, acute deterioration is associated with infection. Herpesviruses have been associated with this disease. Fibrocytes have also been shown to be important in the pathogenesis of pulmonary fibrosis.

Objectives: To develop a murine model for infectious exacerbation of preexisting fibrosis, and provide mechanistic insight into the role of herpesviruses in fibrotic disease.

Methods: We used a model of fluorescein isothiocyanate–induced pulmonary fibrosis in mice. Infection with a murine gammaherpesvirus was given at time of established lung fibrosis. Measurements were made at the time of peak lytic viral replication.

Measurements and Main Results: We demonstrate that infection with gammaherpesvirus can exacerbate established fluorescein isothiocyanate–induced fibrosis evidenced by increased total lung collagen, histologic changes of acute lung injury, and diminished lung function. Gammaherpesvirus can exacerbate preexisting fibrosis in a Th1 cytokine environment and in the absence of Th2 cytokines. Gammaherpesvirus increases fibrocyte recruitment to the lung in wild-type, but not CCR2^–/– mice, in part because viral infection up-regulates production of CCL2 and CCL12, chemokines important for fibrocyte recruitment. In contrast, mouse adenovirus infection did not exacerbate collagen deposition.

Conclusions: These data provide a new model for gammaherpesvirus exacerbation of established pulmonary fibrosis. The up-regulation of chemokines during viral infection and subsequent recruitment of fibrocytes to the lung likely contribute to augmentation of pulmonary fibrosis.

Key Words: chemokine • fibrocyte • Th1/Th2 cytokines • interstitial lung disease

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Herpesviruses have been associated with idiopathic pulmonary fibrosis and exacerbations of fibrosis are associated with high morbidity and mortality. What This Study Adds to the Field This study describes a new animal model for herpesvirus-induced exacerbation of established lung fibrosis and provides a mechanistic description for pathogenesis that includes fibrocyte recruitment.