Effect of bleomycin (5 U/kg) on lung hydroxyproline content of fib–/– and fib+/– mice. Bleomycin (fib+/–, n = 6; fib–/–, n = 5) or PBS (fib+/–, n = 6; fib–/–, n = 3) was instilled intratracheally into fib–/– and fib+/– mice. Twenty-four days after administration, lung hydroxyproline was measured. Data are expressed as mean ± SEM.