We pretreated mice with a Low-density lipoprotein receptor–related protein-1 (LRP1) blocking antibody to test whether LRP1 mediated the cardioprotective signal of SP16 and alpha-1 antitrypsins (AAT). Treatment with the blocking antibody eliminated the protective effects of both SP16 and plasma-derived AAT. n = 5 to 8 mice/group. Ab = antibody; LV = left ventricular.