Cardiac Allograft Vasculopathy is Linked to Impaired Generation of Regulatory M2 Macrophages

Abstract

Purpose There is mounting evidence for the role of innate immunity in acute cardiac allograft rejection, but this does not necessarily extend to cardiac allograft vasculopathy (CAV) and predictors of CAV remain elusive. We hypothesized that circulating monocytes and their derived macrophage subtypes correlate with CAV. Methods 49 consecutive heart transplant recipients ≥ 2 years post-transplant were enrolled. CAV was assessed on angiogram with IVUS by ISHLT and Stanford classification grading. Peripheral blood mononuclear cells were isolated by density gradient centrifugation, with monocytes stained and measured by flow cytometry for classical (CD14++/CD16−), intermediate (CD14++/CD16+), and nonclassical (CD14lo/CD16++) subtypes. Monocytes were cultured into macrophages, driven by M-CSF, and assayed for polarization markers CD86 and CD206. Results were also compared to 22 non-transplant patients with atherosclerotic coronary artery disease (CAD) and healthy controls (no CAD). Results 22 patients had no significant CAV (Stanford class I-II) while 27 had significant CAV (class III-IV). Other than time since transplant (no CAV 77±13 vs CAV 135±12 months), there were no significant differences, including immunosuppression, between the two groups. There were no differences between monocyte subgroups in isolation, but when combined with derived macrophage polarization, patients with CAV had significantly lower M2 (CD206+) macrophage production (0.19±0.04%) than those without CAV (0.45±0.13%), p Conclusion CAV patients are characterized by reduced ability to generate regulatory M2 macrophages. The circulating monocyte and macrophage subtypes differ from those of native CAD and these cell-based markers could be useful to differentiate high vs. low CAV risk phenotypes.