Abstract
Purpose: :
To study the macrophage phenotypes in the macular retina and choroid of patients with and without age-related macular degeneration (AMD), and in the AMD-associated choroidal neovascular membranes (CNVM), graded using the Minnesota Grading System (MGS).
Methods: :
Histology and immunochemistry for CD68 and CD163, and RQ-PCR for CXCL11 and CCL22 transcripts were performed on macular choroidal trephinations (MCTs) from 38 eyes of 19 AMD patients (MGS 3-4) and 18 eyes of 9 non-AMD subjects; and from the microdissected macular retinal cells of 5 atrophic (MGS 4, aAMD), 5 exudative/neovascular AMD (MGS 4, eAMD), and two age-matched normal archived eyes (MGS1). In addition, histology and RQ-PCR for IFN-γ, IL-4, IL-17, IL-18, IL-23, CXCL11, CCL19, CCL17 and CCL22 mRNA were done on surgically excised CNVM from two eAMD patients, un-responsive to bevacizumab therapy.
Results: :
In the MCTs, aging was associated with increased sclerosis and fewer macrophages, especially M2-macrophages, but higher M2 chemokine (CCL22) mRNA. Compared with age-matched non-AMD MCT’s, the advanced AMD specimens showed more sclerosis, fewer M2 macrophages and increases in both M1 and M2 chemokine transcripts with M1:M2 ratio of 8.05 and 1.88 for AMD and non-AMD MCTs, respectively. The retinal cells of the AMD macula had higher M1 (CXCL11) mRNA (34.36±7.17 vs 4.60±3.32, p=0.105), M2 (CCL22) mRNA (4.18±0.29 vs 0.96± 0.07, p<0.001), and a higher ratio of M1/M2 (CXCL11/CCL22) chemokines compared to the controls. The differences were more pronounced in aAMD than eAMD eyes. The CNVMs were either infiltrated with predominantly M1 macrophages with high CXCL11 expression and Th17 lymphocytes with high IL-17 expression, or fibrosis with few M2 macrophages.
Conclusions: :
Normal aging is associated with decreased macrophage infiltration, but increased M2 activities. The macular retinas and MCT’s of advanced AMD eyes show an altered M2 activity and a shift in macrophage activity toward M1. The CNVM from bevacizumab-unresponsive AMD patients reveals aberrant macrophage polarization. Distinct subclasses of macrophages may exert paradoxical effects on local tissues and represent a key mediator in the pathogenesis of AMD. We suggest that M2 macrophages play a protective role in aging retinas. A pathological shift away from protective M2 activity toward the proinflammatory M1 activity or the angiogenic M2 activity is implicated in AMD pathogenesis.
Keywords: age-related macular degeneration • cytokines/chemokines • pathology: human