Background—The innate immune system greatly contributes to the inflammatory process after myocardial infarction (MI). Interleukin-1 receptor–associated kinase-4 (IRAK-4), downstream of Toll/interleukin-1 receptor signaling, has an essential role in regulating the innate immune response. The present study was designed to determine the mechanism by which IRAK-4 is responsible for the cardiac inflammatory process, which consequently affects left ventricular remodeling after MI.

Methods and Results—Experimental MI was created in IRAK-4^-/- and wild-type mice by left coronary ligation. Mice with a targeted deletion of IRAK-4 had an improved survival rate at 4 weeks after MI. IRAK-4^-/- mice also demonstrated attenuated cardiac dilation and decreased inflammation in the infarcted myocardium, which was associated with less proinflammatory and Th1 cytokine expression mediated by suppression of nuclear factor-B and c-Jun N-terminal kinase activation. IRAK-4^-/- mice had fewer infiltrations of CD45⁺ leukocytes and CD11c⁺ dendritic cells, inhibition of apoptosis, and reduced fibrosis and nitric oxide production. Cardiac dendritic cells in IRAK-4^-/- mice were relatively immature or functionally naïve after MI in that they demonstrated less cytokine and costimulatory molecule gene expression. Furthermore, IRAK-4^-/- dendritic cells have less mobilization capacity. Transfer of wild type–derived bone marrow dendritic cells into IRAK-4^-/- mice for functional dendritic cell reconstitution negated the survival advantage and reduced the cardiac dilation observed with IRAK-4^-/- mice at 28 days after MI.

Conclusions—Deletion of IRAK-4 has favorable effects on survival and left ventricular remodeling after MI through modification of the host inflammatory process by blunting the detrimental bone marrow dendritic cells mobilization after myocardial ischemia.