Macrophages and T lymphocytes are the predominant cells in intimal arteritis of resected renal allografts undergoing acute rejection.

Background: In acute renal allograft rejection, T-cell-mediated processes have been generally regarded as dominant. Although there is recent evidence that macrophages play important roles in acute vascular rejection, less is known about the exact proportion of immunocytes in the intimal arteritis of renal allografts with unfavorable outcomes.

Methods: By immunohistochemical staining using nine primary antibodies, we classified the proportions of infiltrating immunocytes in intimal arteritis and glomerulitis in five allografts resected because of acute irreversible graft failure.

Results: All five allografts had features of antibody-mediated rejection based on criteria established by the Banff classification. In intimal arteritis, CD3+ T-lymphocytes accounted for 30.6±13.3% of the immunocytes and macrophages for 40.4±9.2%. 45.4% of the T-cells were CD8+ cytotoxic T-cells. Neutrophils were also present but accounted for a relatively low proportion of the cells (8.8±8.6%). B-cells and plasma cells all accounted for <5% of the immunocytes. NK cells were readily detected (4.2±4.2%). When we compared types of arteritis, the CD15+ neutrophils accounted for as many as 27.8±15.1% of immunocytes in V3 vasculitis and only 1.0±1.4% in V2 vasculitis. CD3+ T-lymphocytes accounted for 25.8±7.3% of immunocytes in V3 vasculitis and 41.5±7.9% in V2 vasculitis. In glomerulitis, the immunocytes were mainly macrophages (53.1±9.1%) and neutrophils (34.6±9.9%).

Conclusion: Macrophages and T-lymphocytes accounted for the highest percentage of immunocytes in the intimal arteritis of irreversible renal failure associated with antibody-mediated rejection. 45.4% of the T-cells were CD8+ cytotoxic T-cells. Neutrophils and NK cells were also present in these lesions. The proportion of neutrophils in V3 vasculitis was much higher than in V2 vasculitis. These observations suggest that besides macrophages and T-lymphocytes, neutrophils may also play a role in the more severe arterial lesion. To our knowledge this is the first report of this observation. Macrophages and neutrophils were the main inflammatory cells in the glomerulitis of acute rejection.