Induction of prolonged infiltration of T lymphocytes and transient T lymphocyte-dependent collagen deposition in mouse lungs following adenoviral gene transfer of CCL18

Objective. Levels of CCL18 are elevated in patients with scleroderma lung disease and other fibrotic pulmonary diseases associated with T lymphocyte involvement. We sought to determine whether CCL18 alone can induce pulmonary T lymphocytic infiltration and fibrosis in mouse lungs. Methods. An adenovirus vector was constructed and used for CCL18 delivery to mouse lungs in vivo. Immunohistochemical, flow cytometric, and enzyme-linked immunosorbent assay analyses were used to assess the resulting changes. Results. Overexpression of CCL18 led to massive perivascular and peribronchial infiltration of T lymphocytes. Although the expression of CCL18 peaked on day 7, the infiltration persisted up to day 64 after infection. The infiltrates were negative for proliferating cell nuclear antigen and TUNEL, suggesting the role of cell trafficking, rather than proliferation and apoptosis, in the infiltration dynamics. Patchy destruction of the alveolar architecture and collagen accumulation in association with the infiltrates were also noticed. These changes were infiltration-dependent, rather than CCL18-dependent, since treatment with antilymphocyte serum completely abrogated the CCL18-induced changes. The infiltrates consisted almost exclusively of T lymphocytes that were minimally activated, with a minimal increase in the expression of CD69 and no changes in the expression of CD25, Fas, FasL, or CD40L. There was no increase in total pulmonary levels of profibrotic cytokines transforming growth factor beta 1 (TGF beta 1) or interleukin-13, although active TGF beta 1 was present locally in association with the infiltrates and areas of distorted alveolar architecture. Prestimulation of primary T lymphocytes with CCL18 in vitro caused an up-regulation of TGF beta 1 and collagen production in T lymphocyte/fibroblast cocultures. Conclusion. CCL18 promotes selective, long-term pulmonary infiltration of T lymphocytes and infiltration-dependent accumulation of collagen through a TGF beta 1-dependent mechanism.