H- 13 : Pathology of renal transplant
H- 14 : acute rejection
Nicolas Kozakowski1, Harald Herkner2, Georg A Böhmig3, Heinz Regele1, Christoph Kornauth1,
Gregor Bond3 and Željko Kikić3
1Institute of Clinical Pathology, Medical University of Vienna, Vienna, Austria
2Department of Emergency Medicine, Medical University of Vienna, Vienna, Austria
3Department of Medicine III, Division of Nephrology and Dialysis, Medical University of Vienna, Vienna,
Austria
Correspondence : Željko Kikić, Department of Medicine III, Division of Nephrology and Dialysis, Medical
University of Vienna, Währinger Gürtel 18-20, Vienna A-1090, Austria. E-mail: zeljko.kikic@meduniwien.ac.at
Journal : Kidney International
Year : 2015 / Month : March
Volume : 88
Pages : 332 –340 doi:10.1038/ki.2015.64
By the Banff classification, the score of peritubular capillaritis, its extent, and its cellular composition should normally be reported in renal allograft pathology. While the score represents an important diagnostic and prognostic variable, the clinical value of capillaritis extent or composition has yet to be resolved. In a retrospective study of 749 renal transplant recipients subjected to 1322 indication biopsies, we found that prevalence scores of 1, 2, or 3 in the biopsy specimens were 10.7, 11.6, and
2.6%, respectively. Focal and diffuse peritubular capillaritis (inflammation over 50% of cortical peritubular capillaries) was diagnosed in 10.5 or 14.4% of cases, respectively. Mononuclear, granulocytic, and mixed peritubular capillaritis was present in 13.1, 3.3, and 8.5%, respectively. While peritubular capillaritis without further subclassification was not related to higher allograft loss rates, a score of 3 (hazard ratio 2.57 (CI: 1.25
–5.28)) and diffuse peritubular capillaritis (1.67 (1.1–2.54)) were significant impartial risk factors for allograft loss. Diffuse peritubular capillaritis was independently associated with features of chronic antibody-mediated rejection and greater eGFR decline after 3 years. In contrast, detailed report of leukocytic composition in peritubular capillaritis did not confer additional prognostic information. Thus, in contrast to typing the infiltrating inflammatory cells, the score and extent of peritubular capillaritis in kidney allograft pathology is essential to assess transplant prognosis.
Keywords: allograft loss; C4d; diffuse capillaritis; GFR; peritubular capillaritis; ptc score

Capillaritis in the renal allograft is important for diagnosis and prognosis. Although glomerulitis has been well studied, peritubular capillaritis has been defined only relatively recently. The finding that peritubular capillaritis severity score and extent may correlate independently with graft outcome mandates further prospective studies to confirm this finding, and to enhance recognition and quantitation of this important lesion.
Antibody-mediated injury is responsible for acute and chronic damage to the renal allograft, compromising function and graft survival in some if not many allografts over time. While arteritis, severe or mild, is seen in some cases of antibody-mediated rejection (AMR), microvascular inflammation is the most common histologic feature of AMR. Microvascular inflammation, defined as accumulation of inflammatory cells in capillaries of the graft, is a key diagnostic feature for the pathologist, even more reliable than capillary deposition of C4d detectable by immunostaining, especially in older allografts.
In addition to diagnostic utility, microvascular inflammation has been shown to predict worse outcome for the graft, correlating with chronic injury and remodeling of glomerular and peritubular capillaries. In the present study, the authors primarily hypothesized that the clinical impact of ptc on allograft outcomes depends on its extent, namely diffuse ptc, and that determining leukocytic subpopulations in ptc might be of comparably lower clinical relevance. To test these hypotheses, they performed a large retrospective cohort study of 1322 indication biopsies and investigated clinical outcomes in univariate and multivariate models in relationship with the different qualities of ptc, namely ptc score, ptc extent, and ptc cellular composition.
The results of this study strongly suggest that the extent of peritubular capillaritis should be taken into account, for prognostic if not diagnostic utility, and should be reported by the pathologist. In addition, future prospective studies should include extent as well as Banff score for peritubular capillaritis, and other scoring options could be considered.
Pr. Jacques CHANARD
Professor of Nephrology