Association of alternatively activated macrophages with unbalanced immune reactions and fibrosis in myocardium of dilatative cardiomyopathy patients with left ventricular assist device implantation

Abstract

Background: Left ventricular assist device (LVAD) support is used as destination therapy in end-stage heart failure. Deterioration of left ventricular (LV) myocardial function correlates with an increased amount of interstitial fibrosis (IF). Development of IF in turn is influenced by the innate immune system through stimulation of alternatively activated macrophages (M2), which secrete cytokines (CK), growth factors and extracellular matrix proteins. M2 transform from polarized resident macrophages, induced by macrophage-activating CK and released into the circulation in active and chronic inflammatory disorders (CID). Objective: We investigated effects of CID in DCM pts with LVAD on immunopathological markers supporting M2 activation and compared levels of IF in LV apex and anterior LV wall of the explanted heart at time of heart transplantation. Methods: Paraffin sections of LV from anterior wall and the site of LVAD implantation at the apex from 13 pts (8-62 y old, 2 female, 9 with CID) were examined on immunohistochemistry and double immunofluorescence/confocal microscopy for subpopulations of macrophages using a pan macrophage marker (CD68) and a specific M2 marker identified by us (stabilin-1). Immunohistochemical findings were correlated with IF, which was quantified on Sirius red stained slides using specific software. Results: Generally, circulating macrophages were solely CD68+. Tissue macrophages showed combined CD68+/stabilin-1+. M2 actin+/CD68-/stabilin-1+ cells were morphologically myofibroblasts. Different quantities of CD68+/stabilin-1+ macrophages were found: single cells in areas without scarring, small clusters in paucicellular scars and large clusters in cellular scars. In pts without CID mean IF (8.5%) was within normal limits (<9%), whereas in CID (asthma, diabetes, rheumatoid arthritis, autoimmune reactions, adipositas) pts total IF was elevated (3-24%, mean 14.6%). No CD68-/stabilin-1+ M2 were demonstrated in the apex or in the explanted heart of pts without CID. In 2 CID pts with short LVAD time (97 d and 26 d resp.), there was still a florid CD68+/stabilin-1+ infiltrate in the explanted heart with large areas of scarring. A higher CD68+/stabilin-1+ cell count in the LV apex was associated with a higher grade of IF in all but 3 patients. These had either a very short or long time on LVAD (26 d, 7 m, 6.5 y). Conclusion: CID appears to initiate inflammatory responses and can influence the repolarization of resting resident myocardial macrophages into M2. High M2 count is associated with larger areas of IF and therefore participates in the remodeling of the human heart.