Effect of MMP-9 deficiency on BAL chemokine accumulation. CC10-rtTA-IL-13 transgene^– and transgene⁺ mice with wild-type and null MMP-9 loci were placed on dox water at 1 month of age and maintained on dox water for an additional 10–60 days as noted. The levels of BAL KC (a), MIP-2 (b), and MCP-1 (c) protein were assessed by ELISA. Circles, CC10-rtTA-IL-13⁺/MMP-9^–/–; diamonds, CC10-rtTA-IL-13⁺/MMP-9^+/+; squares, CC10-rtTA-IL-13^–/MMP-9^+/+. Note that the levels of chemokines in BAL fluids from CC10-rtTA-IL-13 transgene^– mice with null and wild-type MMP-9 loci are superimposed in these graphs. The noted values represent the mean ± SEM of a minimum of six animals at each time point (*P < 0.01).