APC-mediated mortality reduction in bacterial sepsis is seen for QQ41-PAR1 mice but not for QQ46-PAR1 mice. The prosurvival effect of 5A-APC in E coli–induced pneumonia sepsis was tested in Wt and in PAR1 genetically modified mice. Sepsis was induced by instillation of 10⁶ CFU E coli intratracheally. 5A-APC IV treatment was given at 15 minutes before E coli instillation and at 6 hours after infection. QQ41-PAR1 mice, QQ46-PAR1 mice, and Wt littermate controls were observed for survival following E coli infection and 5A-APC treatment over 7 days. Significance was analyzed using log rank. *P < .01.