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BACKGROUND	After 9/11/2001 , most FDNY workers had persistent lung function decline but some exposed workers recovered .
BACKGROUND	We hypothesized that the protease/anti-protease balance in serum soon after exposure predicts subsequent recovery .
METHODS	We performed a nested case-control study measuring biomarkers in serum drawn before 3/2002 and subsequent forced expiratory volume at one second ( FEV1 ) on repeat spirometry before 3/2008 .
METHODS	Serum was assayed for matrix metalloproteinases ( MMP-1 ,2,3,7,8,9,12 and 13 ) and tissue inhibitors of metalloproteinases ( TIMP-1 ,2,3,4 ) .
METHODS	The representative sub-cohort defined analyte distribution and a concentration above 75th percentile defined elevated biomarker expression .
METHODS	An FEV1 one standard deviation above the mean defined resistance to airway injury .
METHODS	Logistic regression was adjusted for pre-9 / 11 FEV1 , BMI , age and exposure intensity modeled the association between elevated biomarker expression and above average FEV1 .
RESULTS	FEV1 in cases and controls declined 10 % of after 9/11/2001 .
RESULTS	Cases subsequently returned to 99 % of their pre-exposure FEV1 while decline persisted in controls .
RESULTS	Elevated TIMP-1 and MMP-2 increased the odds of resistance by 5.4 and 4.2 fold while elevated MMP-1 decreased it by 0.27 fold .
CONCLUSIONS	Resistant cases displayed healing , returning to 99 % of pre-exposure values .
CONCLUSIONS	High TIMP-1 and MMP-2 predict healing .
CONCLUSIONS	MMP/TIMP balance reflects independent pathways to airway injury and repair after WTC exposure .

