Background: Macrophages in renal transplants have been shown to participate in antibody-mediated rejection and are associated with impaired renal function. We calculated the glomerular macrophage index (GMI) in a large transplant biopsy cohort, studied its quantity in different diagnostic groups, to clarify its possible impact on graft survival.
Methods: GMI, defined as the mean number of macrophages in 10 glomeruli, was prospectively quantified in 1440 renal transplant biopsies over a 10-year period. The main histopathological diagnoses were grouped into eight disease entities, and GMI was compared to normal transplant biopsies as the reference group. The impact of GMI on graft survival was analyzed.
Results: GMI was highest in chronic (mean 9.4) and active (9.7) antibody mediated rejections (ABMR), mixed rejections (7.6), and recurrent or de novo glomerulonephritis (7.5) and differed significantly from normal transplants (1.3) in almost all diagnostic groups. Hazard ratios for graft loss were significantly increased for all biopsies with GMI ≥1.9 compared to GMI < .5 (reference group) in an adjusted Cox regression model and increased with higher GMI levels. Biopsies with GMI ≥ 4.6 had < 60% 10-year graft-survival, compared to > 80% with GMI ≤ 1.8.
Conclusion: GMI levels were predictive of graft loss independent of histological diagnoses and may guide clinicians to decide follow-up and therapy.
Keywords: glomerular macrophage index; graft outcome; macrophage; rejection; renal transplant biopsies.
© 2022 The Authors. Clinical Transplantation published by John Wiley & Sons Ltd.