Expression of Receptor Activator of Nuclear Factor-Kappa B Ligand in Leucocytes During Acute Kidney Rejection after Transplantation in Rats

Abstract

Introduction: Acute cellular rejection of the transplanted kidney is an important cause of impaired graft function. One of the basic characteristics of acute cellular rejection according to the latest Banff classification of renal allograft pathology is the presence of T lymphocytes in a large number in allograft tissue. Recent studies have shown the important role of T lymphocytes and macrophages in acute cellular rejection of kidney allograft. Osteoprotegerin (OPG), receptor activator of nuclear factor-kappa B (RANK) and RANK ligand (RANKL) are three relatively novel members of the tumor necrosis factor (TNF) superfamily. They have a crucial role in physiological and pathological bone metabolism but also in immunological processes. The aim of our study was to determine the expression of RANKL and RANK by T lymphocytes and macrophages in acute cellular kidney allograft rejection in rats. Methods: The study included 15 male Wistar rats (3 months old; weight 250-300g) as recipients and 15 male DA rats (3 months old; weight 250-300g) as donors. Animals were sacrificed after 3 weeks and the transplanted kidney was extracted and processed for pathohistological analysis and immunoflorescence. The latest Banff classification of renal allograft pathology was used on all tissue samples by two experienced pathologists. In all tissue samples acute cellular rejection was proven. Acute cellular rejection kidney sections were examined by dual- labeled immunofluorescence to detect CD4, CD8 or CD68 (red) and RANK or RANKL (green) allowing clear definition of cells that co-express both (orange). Results: Cytoplasmic and on surface granular RANKL immunoreaction on fluorescence microscopy of various intensities was detected in all tissue samples. RANKL positive expression was colocalized with CD4+ and CD8+T lymphocytes in acutely rejected kidney tissue. There was no association between CD4+ and CD8+T cells with RANK expression in any obtained sample. RANK but not RANKL, was expressed by infiltrating CD68 positive macrophages in the interstitium of kidney tissue. Conclusion: RANK and RANKL are expressed by T lymphocytes and macrophages in acute cellular kidney rejection after transplantation in rats. They have a possible immunomodulatory role in acute cellular kidney rejection. Serum concentration of RANKL could be a marker for early detection of acute cellular kidney rejection.