Although to date we have not extensively characterized the ECM derived from Thy-1(+) lung fibroblasts cultured in vitro, it is plausible to infer that it is similar to the lung ECM in young mice and our experimental findings provide a potential mechanism to explain why young mice do not develop the degree lung fibrosis in response to bleomycin as do older mice. The gene discussed is THY1; the disease is pulmonary fibrosis.