A. PAI-1 KO mice fail to induce early pro-inflammatory responses against NTHi infection. PAI-1 KO mice and their littermate WT control mice were i.t. inoculated with NTHi or saline as a control, and mRNA expression of pro-inflammatory cytokines IL-1β and TNF-α and chemokines KC and MIP-2 were measured from the lung tissues of mice 6 hours after NTHi inoculation. B. Polymorphonuclear (PMN) leukocyte migration was inhibited in PAI-1 KO mice following NTHi infection. PAI-1 KO and littermate WT mice were i.t. inoculated with NTHi or saline as a control, and PMN cells migrated into lung was measured from BALF of mice inoculated with NTHi or control. C & D. PAI-1 KO mice showed reduced bacterial clearance against NTHi infection. PAI-1 KO and littermate WT mice were i.t. inoculated with NTHi, and in vivo bacteria growth was measured from the lung tissues of mice 24 hours after NTHi inoculation (C), and body temperature was measured before sacrifice (D). E. Loss of early defense against NTHi infection in PAI-1 KO mice results in enhanced inflammation at late stage of infection. PAI-1 KO and littermate WT mice were i.t. inoculated with NTHi, and mRNA expression of pro-inflammatory cytokines IL-1β and TNF-α and chemokine MIP-2 was measured from the lung tissues of mice 6, 24, and 48 hours after NTHi infection. The values presented in A - D are Mean ± SD (n=3 in A & B, n=10 in C & D). *, p<0.05 compared with CON in WT; **, p<0.05 compared with NTHi in WT. The values presented in E are Mean ± SD (n=3); *, p<0.05 compared with NTHi in WT. CON: control; WT: wild-type; KO: knock-out.