Eosinophils and T Lymphocytes Possess Distinct Roles in Bleomycin-Induced Lung Injury and Fibrosis

Abstract

Leukocyte infiltration is characteristic of lung injury and fibrosis, and its role during tissue repair and fibrosis is incompletely understood. We found that overexpression of IL-5 in transgenic mice (IL-5TG) or by adenoviral gene transfer increased bleomycin (blm)-induced lung injury, fibrosis, and eosinophilia. Surprisingly, blm-treated IL-5-deficient (IL-5−/−) mice also developed pronounced pulmonary fibrosis but characterized by marked T lymphocyte infiltration and absence of eosinophilia. In both murine strains however, induction of lung TGF-β expression was evident. Purified lung eosinophils from blm-treated IL-5TG mice stimulated α-smooth muscle actin and collagen expression in mouse lung fibroblasts, without affecting proliferation. Furthermore instillation of purified eosinophils into murine lungs resulted in extension of blm-induced lung fibrosis, thus confirming a role for eosinophils. However, lung T lymphocytes from blm-treated IL-5−/− mice were able to stimulate fibroblast proliferation but not α-smooth muscle actin or collagen expression. Blocking T cell influx by anti-CD3 Abs abrogated lung fibrosis, thus also implicating T lymphocytes as a key participant in fibrosis. Pulmonary fibrosis in IL-5TG mice was preferentially associated with type 2 cytokines (IL-4 and IL-13), whereas fibrotic lesions in IL-5−/− animals were accompanied by proinflammatory cytokine (TNF-α, IL-1β, and IFN-γ) expression. We suggest that eosinophils and T cells contribute distinctly to the development of blm-induced lung fibrosis potentially via their production of different cytokine components, which ultimately induce TGF-β expression that is intimately involved with the fibrosis.

Complex Regulation of Pulmonary Inflammation and Fibrosis by CCL18

“…Treatment of mice with antilymphocyte serum before the administration of AdV-CCL18 did not affect CCL18 expression in the lung (real-time PCR and ELISA data not shown) but resulted in complete abrogation of the perivascular and peribronchial infiltration and collagen accumulation consistent with our previous report. 11 Consistent with previous reports of others, 22,23,25 treatment with antilymphocyte serum did not have a significant effect on collagen accumulation in the bleomycin injury model (P Ͼ 0.05, Student's t-test, data not shown). In the combined CCL18 overexpression and bleomycin injury model treated with antilymphocyte serum, pulmonary levels of collagen did not differ from the bleomycin injury alone treated with antilymphocyte serum (205.8 Ϯ 14.1 versus 199 Ϯ 12.3 g/lung, respectively, P Ͼ 0.05, Student's t-test, data not shown).…”

“…2,19 -22 Although not all pulmonary fibrotic processes are T-lymphocyte-dependent, [23][24][25] previous studies suggested that T lymphocytes do contribute to regulation of fibrosis in the lung in human disease 1,2,19 -21 and in animal models of pulmonary fibrosis. 22,26,27 In contrast to pulmonary T lymphocytes, macrophages are by far the most abundant cell type in the lungs, normally constituting more than 85% of bronchoalveolar lavage cells. 2 Although the percentage of macrophages declines during lung inflammation due to influx of T cells and other inflammatory cells, macrophages undergo phenotypic changes associated with inflammation and fibrosis 1 and establish a vicious circle of pulmonary fibrosis by further up-regulating CCL18 expression.…”

“…22,34,35 We first instilled mice with AdV-CCL18 as described 11 and then, at the peak of CCL18 production (day 7), performed a second intratracheal instillation with either PBS (as a control) or bleomycin in a lower (0.01 U/mouse) or higher (0.03 U/mouse) dose to induce lung inflammation and fibrosis. Of note, the selected doses of bleomycin alone were found to be insufficient to achieve a plateauing effect on lung inflammation and fibrosis in preliminary experiments (data not shown).…”

Evasion of myofibroblasts from immune surveillance: A mechanism for tissue fibrosis

“…The functional role of immune cells in lung injury (and repair) and fibrosis is multifaceted (1,(11)(12)(13). To shed more light on one aspect of this issue, we evaluated the specific interaction between immune T cells and lung myofibroblasts in vitro and in vivo.…”

Towards Systems Biology of Human Pulmonary Fibrosis

“…We have data to support the role of alveolar epithelial cells, myofibroblasts, circulating mesenchymal pleuripotent cells, T cells, macrophages, and endothelial cells in lung fibrosis (8)(9)(10). The success of these studies has presented us with a biological Rashô mon.…”