Background Myocardial infarction (MI) is the leading cause of death worldwide. Following ischemia/reperfusion (I/R) injury a precisely controlled immune response is necessary for preservation of cardiac integrity. In its course, immune cells interact with dead and damaged cells via a variety of cell surface molecules. One such interaction revolves around signal regulatory protein α (SIRPα) on myeloid cells and ubiquitously expressed CD47, which inhibits phagocytosis and was thus termed an innate immune checkpoint. Inhibition of CD47 via antibodies was shown to be protective in other I/R injury of eg liver and kidney, mostly by modulation of nitric oxide (NO) related pathways. Whether it is also beneficial in myocardial I/R injury remains to be seen.

Methods & Results We determined I/R injury size in murine hearts after anti-CD47 treatment using the triphenyl tetrazolium chloride (TTC)/Evans blue test and found decreased TTC negative per area at risk (AAR) at 24 h of reperfusion when compared to IgG antibody treated mice. Likewise ejection fraction was higher and plasma cardiac Troponin I (cTNI) levels were lower in anti-CD47 treated animals at the same time point. We further studied immune cell populations using flow cytometry, which revealed similar levels of neutrophils at 24 h of reperfusion in both anti-CD47 and control groups. To investigate this paradox, we deployed cutting edge light sheet fluorescence microscopy (LSFM) to simultaneously measure I/R injury size and immune cell levels and indeed found a higher ratio of neutrophils per injured area in CD47 treated mice. Furthermore, in these animals neutrophil populations were localized outside the injured area rather than only just inside, as was the case in the control group. We further measured cardiac reactive oxygen species (ROS) concentration and found ROS levels to be slightly decreased after CD47 injections following I/R. In contrast to results from other I/R injury models, we could not find an influence of anti-CD47 treatment on nitrate/nitrite/NO pathways.

Conclusion Anti-CD47 treatment was shown to be protective in various I/R injury models. We could also demonstrate reduced infarct sizes after 24 h of reperfusion. This was not associated with decreased levels of neutrophils, which also located only outside of the injured area. Whether this is beneficial for the long term outcome, remains to be investigated. Nevertheless CD47 blockade presents as a highly novel and promising approach to AMI treatment and warrants further research.