Differential role for T cells in the development of fibrotic lesions associated with reovirus 1/L-induced bronchiolitis obliterans organizing pneumonia versus Acute Respiratory Distress Syndrome.

Bronchiolitis obliterans organizing pneumonia (BOOP) and Acute Respiratory Distress Syndrome (ARDS) are two pulmonary diseases with fibrotic components. BOOP is characterized by perivascular/peribronchiolar leukocyte infiltration leading to the development of infra-alveolar fibrosis. ARDS is a biphasic disease that includes an acute phase, consisting of severe leukocyte infiltration, edema, hemorrhage, and the formation of hyaline membranes, and a chronic phase, which is characterized by persistent infra-alveolar and interstitial fibrosis. CBA/J mice infected with 1 X 106 plaque-forming units (pfu) reovirus 1/L develop follicular bronchiolitis and infra-alveolar fibrosis similar to BOOP. In contrast, CBA/J mice infected with 1 X 107 pfu reovirus 1/L develop histologic characteristics of ARDS including diffuse alveolar damage, hyaline membranes, and intra-alveolar fibrosis. In this report, we demonstrate a differential role for T lymphocytes in the development of fibrosis associated with BOOP versus ARDS. Neonatally thymectomized CBA/J mice infected with 1 X 10(7) pfu (ARDS) reovirus 1/L still develop the hallmark characteristics of ARDS, including a severe viral pneumonia with cellular infiltrates comprised mainly of macrophages and neutrophils, hyaline membrane formation, and hemorrhage during the acute phase of the disease and persistent infra-alveolar fibrosis during the chronic phase of the disease. In contrast, neonatally thymectomized CBA/J mice infected with 1 X 106 pfu (BOOP) reovirus 1/L do not develop infra-alveolar fibrosis associated with BOOP. Therefore, while T cells are necessary for the development of intraluminal fibrosis associated with BOOP, they are not necessary for the development of intraluminal fibrosis associated with ARDS. Furthermore, we suggest that interferon-gamma plays a key role in the fibrotic process and that elevated levels of interferon-gamma are associated with a continuum from least to more severe fibrosis.