Infiltration of Macrophages Correlates with Severity of Allograft Rejection and Outcome in Human Kidney Transplantation

Abstract

Objective: Despite substantial progress in recent years, graft survival beyond the first year still requires improvement. Since modern immunosuppression addresses mainly T-cell activation and proliferation, we studied macrophage infiltration into the allografts of 103 kidney transplant recipients during acute antibody and T-cell mediated rejection. Macrophage infiltration was correlated with both graft function and graft survival until month 36 after transplantation.

Results: Macrophage infiltration was significantly elevated in antibody-mediated and T-cell mediated rejection, but not in kidneys with established IFTA. Treatment of rejection with steroids was less successful in patients with more prominent macrophage infiltration into the allografts. Macrophage infiltration was accompanied by increased cell proliferation as well as antigen presentation. With regard to the compartmental distribution severity of T-cell-mediated rejection was correlated to the amount of CD68+ cells especially in the peritubular and perivascular compartment, whereas biopsies with ABMR showed mainly peritubular CD68 infiltration. Furthermore, severity of macrophage infiltration was a valid predictor of resulting creatinine values two weeks as well as two and three years after renal transplantation as illustrated by multivariate analysis. Additionally performed ROC curve analysis showed that magnitude of macrophage infiltration (below vs. above the median) was a valid predictor for the necessity to restart dialysis. Having additionally stratified biopsies in accordance to the magnitude of macrophage infiltration, differential CD68+ cell infiltration was reflected by striking differences in overall graft survival.

Conclusion: The differences in acute allograft rejection have not only been reflected by different magnitudes of macrophage infiltration, but also by compartment-specific infiltration pattern and subsequent impact on resulting allograft function as well as need for dialysis initiation. There is a robust relationship between macrophage infiltration, accompanying antigen-presentation and resulting allograft function.

Fig 1. Allograft rejection enhances cellular infiltration.

Quantity of CD68 (A), Ki67 (B), and MHCII-HLA-DR (C) positive cells in renal allograft biopsies dependent on underlying histopathological category. # p < 0.05 vs. normal histology. ABMR = antibody mediated rejection, TCMR- = T-cell mediated rejection without arteritis; TCMR+ = T-cell mediated rejection with arteritis; IFTA = interstitial fibrosis/tubular atrophy.

Fig 2. Compartment-specific macrophages expression.

Compartment-specific expression (peritubular (A), glomerular (B), perivascular (C)) of CD68 positive macrophages in renal allograft biopsies dependent on histological grading. # p < 0.05 vs. normal histology; * p < 0.05 vs TCMR without arteritis. D: CD68 expression in a representative biopsy (TCMR with arteritis).

Fig 3. Compartment-specific cellular proliferation.

Compartment-specific expression (peritubular (A), glomerular (B), perivascular (C)) of Ki67 positive cells in renal allograft biopsies dependent on histopathological grading. # p < 0.05 vs. normal histology;; * p < 0.05 vs TCMR without arteritis. D: left-hand side: Ki67 expression in a representative biopsy (TCMR with arteritis); right-hand side: representative example of a Ki67 (green) /CD68 (red) costaining (orange arrow).

Fig 4. Compartment-specific antigen expression.

Compartment-specific expression (peritubular (A), glomerular (B), perivascular(C)) of MHCII-HLA-DR positive cells in renal allograft biopsies dependent on histopathological grading. # p < 0.05 vs. normal histology. D: Representative slide of a CD68-MHCII-HLADR costaining in a TCMR with arteritis biopsy.

Fig 5. Consequences of macrophages infiltration for renal function and graft survival.

A: Association of CD68+ cell infiltration (below vs. above the median of macrophage infiltration) with corresponding serum creatinine values until 36 months after transplantation. # p < 0.05. B: ROC curve analysis on impact of CD68 infiltration for need for dialysis initiation (12months/36 months after transplantation). C: Kaplan-Meier curve for corresponding overall graft survival (below vs. above the median)