# Shifting landscapes: dynamic changes from pro- to anti-inflammatory leukocyte phenotype in myocardial ischemia/reperfusion injury

## TL;DR

This study explores how immune cells change from pro- to anti-inflammatory in heart tissue after a heart attack and reperfusion.

## Contribution

The study reveals dynamic shifts in leukocyte phenotypes and their role in platelet-leukocyte complex formation after myocardial I/R injury.

## Key findings

- Anti-inflammatory Ly6Clow monocytes and N2 neutrophils form platelet-leukocyte complexes after myocardial infarction.
- Expression of CD206-GMFI in neutrophils increases by day 7, indicating an anti-inflammatory shift.
- Ly6Clow monocytes decrease significantly as early as day 3 post-injury.

## Abstract

The temporal and spatial dynamics of platelet–leukocyte complex (PLC) formation in myocardial ischemia reperfusion injury (I/R injury) are still ill defined.

To investigate the kinetics and spatial differences of platelet-monocyte (PMC) and platelet-neutrophil (PNC) complex formation over the first 7 days in a mouse model of myocardial I/R injury.

A time-course study was conducted up to 7 days in order to evaluate immune cell response and cardiac function following myocardial I/R injury in mice. Myocardial I/R injury was induced by ligation of the left anterior descending coronary artery (LAD) for 30 min followed by reperfusion. Using flow cytometry leukocyte and platelet markers were evaluated in the heart, blood, spleen, and bone marrow. Echocardiography was performed in order to measure ejection fraction and fractional shortening which are accepted indicators of cardiac function.

Expression of CD206-Geometric Mean Fluorescence Intensity (GMFI) indicative of an anti-inflammatory phenotype in neutrophils (N2) increased in PNCs at day 7. A statitstically significant decrease in the percentage of anti-inflammatory Ly6Clow PMCs was observed as early as day 3, when compared to the baseline value. Flow cytometry analysis showed no significant variations in PNCs or PMCs within the area at risk (AAR) across the specified time points. A rise in neutrophils and monocytes was observed in the AAR, reaching its peak on day 3.

The present study demonstrates that both anti-inflammatory Ly6Clow monocytes and N2 neutrophils participate in PLC formation following myocardial infarction (MI) and reperfusion. Our results suggest that the N2 phenotype prerequisite for PLC formation in AAR at day 7. These findings suggest that targeted interventions may be developed to improve outcomes after myocardial I/R injury.