Thickening of the peritubular capillary basement membrane is a useful diagnostic marker of chronic rejection in renal allografts

Clinicopathological Analyses of Chronic Renal Allograft Arteriopathy after Kidney Transplantation

INTRODUCTION

Herein, we discuss clinicopathological analyses of cases of chronic renal allograft arteriopathy (CRA) after renal transplantation and clarify the mechanisms underlying the development and prognostic significance of CRA.

METHODS

CRA was diagnosed in 34 renal allograft biopsy specimens (BSs) obtained from 27 renal transplant patients who were followed up at the Department of Urology and Transplant Surgery, Toda Chuo General Hospital, between January 2010 and December 2020.

RESULTS

CRA was diagnosed at a median of 33.4 months post-transplantation. Of the 27 patients, 16 had a history of rejection. Among the 34 BSs showing evidence of CRA, CRA was mild (cv1 in Banff's classification) in 22, moderate (cv2) in 7, and severe (cv3) in 5 patients. We then classified the 34 BSs showing evidence of CRA based on their overall histopathological features as follows: cv alone seen in 11 (32%) BSs, cv + antibody-mediated rejection (AMR) in 12 (35%), and cv + T-cell-mediated rejection (TCMR) in 8 (24%). Loss of the renal allograft occurred during the observation period in 3 patients (11%). Of the remaining patients with functioning grafts, deterioration of renal allograft function after biopsies occurred in 7 cases (26%).

CONCLUSIONS

Our study results suggest that AMR contributes to CRA in 30-40% of cases, TCMR in 20-30% of cases, isolated v lesions in 15% of cases, and cv lesions alone in 30%. The intimal arteritis was a prognostic factor in CRA.

Clinical and Pathological Analyses of Borderline Changes Cases after Kidney Transplantation

<b><i>Aim:</i></b> We aimed to perform a clinicopathological analysis of cases presenting with borderline changes (BC) after renal transplantation and discuss whether BC might be clinically or pathologically important. <b><i>Materials and Methods:</i></b> BC was diagnosed in 22 renal allograft biopsy specimens obtained from 20 renal transplant recipients between April 2010 and March 2019 after follow-up at the Department of Transplant Surgery, Kidney Center, Toda Chuo General Hospital. <b><i>Results:</i></b> BC was diagnosed at a median of 500 days following transplantation. Among the 22 renal allograft biopsy specimens showing evidence of BC, tubulitis was observed in all specimens. Interstitial inflammation was present in 18 specimens (82%), peritubular capillaritis in 14 (64%), interstitial fibrosis (ci) and tubular atrophy (ct) in 4 (18%), and C4d deposition in the peritubular capillary was present in 6 specimens (27%). Glomerulitis and intimal arteritis were not observed. There was no renal graft loss during the observation period, but deterioration of renal allograft function after biopsy occurred in 9 patients (45%). <b><i>Conclusions:</i></b> In BC, tubulitis and interstitial inflammation were the main constituents. Because glomerulitis was not observed in our study, we suspect that BC contributes to acute T-cell-mediated rejection. Although BC did not lead to renal graft loss, renal graft function deterioration was seen in nearly half of the patients after the renal graft biopsy. We conclude that BC is important clinically and pathologically and needs to be monitored and treated appropriately.

Clinicopathologic Analyses of Chronic Vascular Rejection After Kidney Transplantation

AIM

We discuss the clinicopathologic analyses of cases of biopsy specimens (BS) after renal transplantation and clarify the mechanisms underlying the development and prognostic significance of chronic vascular rejection (CVR).

PATIENTS

CVR was diagnosed in 30 renal allograft BS obtained from 23 renal transplant patients being followed up at the Department of Urology and Transplant Surgery, Toda Chuo General Hospital, between January 2010 and August 2017.

RESULTS

CVR was diagnosed at a median of 33.1 months post-transplantation. Among the 23 patients, 14 had a history of rejection. Among the 30 BS showing evidence of CVR, the CVR was mild (cv1 on Banff's classification) in 19, moderate (cv2) in 6, and severe (cv3) in 5. We then classified the 30 BS showing evidence of CVR by their overall histopathologic features as follows: cv alone was seen in 9 (30%), cv + antibody-mediated rejection (AMR) in 11 (37%), and cv + T-cell-mediated rejection (TCMR) in 8 (27%). Loss of the renal allograft occurred during the observation period in 2 patients (9%). Of the remaining patients with functioning grafts, deterioration of the renal allograft function after the biopsies occurred in 6 (26%).

CONCLUSIONS

Our study results suggest that AMR contributes to CVR in 30% to 40% of cases, TCMR in 20% to 30% of cases, isolated v lesions in 10% of cases, and cv lesions alone in 30%. The prognosis of the graft exhibiting CVR was not too poor even under the present immunosuppressive protocol.

Diagnosis of renal transplant rejection: Banff classification and beyond

Diagnosis of renal transplant rejection is dependent on interpretation of renal allograft biopsies. The Banff Classification of Allograft Pathology, which was developed as a standardized working classification system in 1991, has contributed to the standardization of definitions for histologic injuries resulting from renal allograft rejections and provided a universal grading system for assessing these injuries. It has also helped to provide insight into the underlying pathogenic mechanisms that contribute to transplant rejection. In addition to histological and immunologic parameters, molecular tools are now being used to facilitate the diagnosis of rejection. In this review, I will discuss morphologic features of renal transplant rejections as well as major revisions and pitfalls of the Banff classification system, and provide future perspectives.

The Use of Digital Microscopy to Compare the Thicknesses of Normal Corneas and Ex Vivo Rejected Corneal Grafts with a Focus on the Descemet's Membrane

Objective

To compare the thickness of corneal layers, specifically the Descemet's membrane (DM), in normal corneas and in failed grafts due to rejection (FGRs) using the digital histopathology and to propose a model for the measurement of corneal layers using this method.

Methods

This is a prospective, cross-sectional study performed at the MUHC-McGill University Ocular Pathology & Translational Research Laboratory (McGill University, Montreal, Canada). Histopathological sections of 25 normal human corneas and 40 FGRs were fully digitalized and examined. Inclusion criteria: samples diagnosed as normal corneas or FGRs, from patients older than 18 years of age. Exclusion criteria: histopathological sections without adequate tissue or missing epidemiological information. For each sample, the thicknesses of the epithelium, stroma, and DM were acquired. From a perpendicular plane of reference, two central measurements and two nasal and two temporal peripheral measurements were obtained.

Results

There were differences between the normal and FGR groups in the mean central thickness of the epithelium (p < 0.001), the nasal and temporal stromal regions (p < 0.001), and of the DM in the nasal and temporal regions (p < 0.001). Compared with the extremities of the sample (nasal and temporal), the mean thickness of the DM in normal corneas was lower in the central region (p < 0.001), and this difference was not found in the FGR group.

Conclusions

Normal corneas have a thinner epithelium in the central region than the FGR group. In addition, the stroma and DM thicknesses of the nasal and temporal periphery were significantly higher in normal corneas than in those from the FGR group. The digital microscopy protocol applied in this study may be useful for further research studies regarding cornea and other tissues.

Immunoenzymatic Staining of Caveolin-1 in Formalin-Fixed Renal Graft Showing Chronic Antibody Mediated Rejection

AIM

Caveolin-1 (CAV-1) is a molecule associated with endothelial cell dysfunction in chronic antibody-mediated rejection (CAMR) and considered to be a novel biomarker of CAMR. For immunohistochemical staining to reveal CAV-1 expression, most studies have used immunofluorescent stained frozen specimens, whereas formalin-fixed tissues have not been utilized. In the present study, we examined CAV-1 expression in specimens from CAMR patients using an immunoenzymatic technique with formalin-fixed tissues.

METHODS

Eleven patients diagnosed with CAMR based on findings of transplanted renal biopsy samples were enrolled. Those biopsy specimens were formalin fixed and stained with CAV-1 using an immunoenzymatic method. Dye extent was evaluated by classifying that in peritubular capillaries (PTC) and glomerular capillaries (GBM) in 3 steps. We then compared the Banff scores for peritubular capillaritis (ptc), glomerulopathy (cg), and C4d using those results.

RESULTS

CAV-1 expression was confirmed in vascular endothelium (PTC, GBM), while it was poor in epithelial cells. A Banff score for ptc and cg of 3 points was seen in 3 and 4 cases, of 2 points was seen in 1 and 4 cases, of 1 point was seen in 7 and 3 cases, and of 0 points was seen in 0 and 0 cases, respectively. In PTC, C4d and CAV-1 scores of 3 points were seen in 0 and 9 cases, of 2 points were seen in 2 and 2 cases, of 1 point was seen in 5 and 0 cases, and of 0 points were seen in 4 and 0 cases, respectively. As for GBM, C4d and CAV-1 scores of 3 points were seen in 8 and 7 cases, of 2 points were seen in 2 and 4 cases, of 1 point was seen in 0 and 0 cases, and of 0 points were seen 1 and 0 cases, respectively.

CONCLUSION

CAV-1 expression in PTC had a score ≥2 in all cases, indicating that an adequate level of staining of formalin-fixed tissue was attained with the present immunoenzymatic technique. These results suggest that CAV-1 expression examined by the present method may be useful for identifying endothelial dysfunction.

Comparison of endothelial/Descemet's membrane complex thickness with endothelial cell density for the diagnosis of corneal transplant rejection

Purpose:

This study compared the effectiveness of endothelial/Descemet’s membrane complex thickness obtained using high-definition anterior segment optical coherence tomography with endothelial cell density obtained using confocal microscopy as diagnostic tools in predicting corneal transplant rejection.

Methods:

This observational, prospective, cross-sectional study evaluated penetrating keratoplasty grafts. Slit lamp examination organized the grafts into healthy or rejecting grafts. Grafts were scanned using both high-definition anterior segment optical coherence tomography and confocal microscopy. Central corneal thickness, endothelial/Descemet’s membrane complex thickness, endothelial cell density, and coefficient of variation were each compared with the clinical status. Descemet’s rejection index, defined by endothelial/Descemet’s membrane complex thickness divided by central corneal thickness multiplied by 33, further compared endothelial/Descemet’s membrane complex thickness with central corneal thickness.

Results:

Endothelial/Descemet’s membrane complex thickness, central corneal thickness, and Descemet’s rejection index were all able to differentiate between clear and rejected corneal grafts (p < 0.0001, p = 0.001, and p = 0.012, respectively). Endothelial cell density and coefficient of variation did not correlate with the clinical status (p = 0.054 and p = 0.102, respectively). Endothelial/Descemet’s membrane complex thickness had the largest area under the curve using receiver operating characteristic curves (p < 0.0001). Endothelial/Descemet’s membrane complex thickness had a sensitivity of 86% and specificity of 81% with a cutoff value of >16.0 µm (p < 0.0001). The sensitivity and specificity of endothelial cell density were both 71% with a cutoff value of ⩽897 cells/mm² (p = 0.053). There was a high correlation between endothelial/Descemet’s membrane complex thickness and both Descemet’s rejection index and central corneal thickness (p < 0.0001).

Conclusion:

Endothelial/Descemet’s membrane complex thickness measured by high-definition anterior segment optical coherence tomography is a useful parameter for the diagnosis of corneal graft rejection. The diagnostic performance of endothelial/Descemet’s membrane complex thickness was significantly better than that of endothelial cell density and central corneal thickness. Endothelial cell density and the coefficient of variation were unable to diagnose corneal graft rejection in our cross-sectional study.

Clinical and Pathological Analyses of Cases of Acute Vascular Rejection After Kidney Transplantation

BACKGROUND

We performed a clinical and pathological analysis of cases of acute vascular rejection (AVR), characterized by intimal arteritis and transmural arteritis (Banff v score) after kidney transplantation, in an attempt to clarify the mechanisms underlying the development and prognostic significance of AVR.

METHODS

AVR (Banff score: v >0) was diagnosed in 31 renal allograft biopsy specimens (BS) obtained from 31 renal transplant patients receiving follow-up care at the Department of Urology, Tokyo Women's Medical University, between January 2010 and April 2016.

RESULTS

AVR was diagnosed at a median of 124.6 days after transplantation. Among the 31 BS showing evidence of AVR, AVR was mild (v1 in Banff's classification) in 25 cases, moderate (v2) in 6, and severe (v3) in none. We classified the 31 BS with evidence of AVR by their overall histopathological features as follows: isolated v lesions were observed in 6 BS, acute antibody-mediated rejection (AAMR) in 7, acute T-cell-mediated rejection (ATCMR) in 12, and both ATCR and AAMR in 6. Loss of the renal allograft occurred during the observation period in 3 patients, and, of the remaining cases with functioning grafts, deterioration of renal allograft function after biopsy occurred in only 2 patients.

CONCLUSIONS

The results of our study suggest that ATCMR contributes to AVR in 40% to 60% of cases, AAMR in 20% to 40% of cases, and isolated v lesions in 20% of cases. The prognosis of the patient with the graft that had AVR was relatively good under the present immunosuppression protocol and current anti-rejection therapies.

Descemet Membrane Thickening as a Sign for the Diagnosis of Corneal Graft Rejection: An Ex Vivo Study

PURPOSE

To disclose, using an ex vivo study, the histopathological mechanism behind in vivo thickening of the endothelium/Descemet membrane complex (En/DM) observed in rejected corneal grafts (RCGs).

METHODS

Descemet membrane (DM), endothelium, and retrocorneal membranes make up the total En/DM thickness. These layers are not differentiable by high-definition optical coherence tomography; therefore, the source of thickening is unclear from an in vivo perspective. A retrospective ex vivo study (from September 2015 to December 2015) was conducted to measure the thicknesses of DM, endothelium, and retrocorneal membrane in 54 corneal specimens (31 RCGs and 23 controls) using light microscopy. Controls were globes with posterior melanoma without corneal involvement.

RESULTS

There were 54 corneas examined ex vivo with mean age 58.1 ± 12.2 in controls and 51.7 ± 27.9 years in RCGs. The ex vivo study uncovered the histopathological mechanism of En/DM thickening to be secondary to significant thickening (P < 0.001) of DM (6.5 ± 2.4 μm) in RCGs compared with controls (3.9 ± 1.5 μm).

CONCLUSIONS

Our ex vivo study shows that DM is responsible for thickening of the En/DM in RCGs observed in vivo by high-definition optical coherence tomography and not the endothelium or retrocorneal membrane.

[The pathology of renal transplants]

In order to make an objective assessment of the histopathology of a renal biopsy during a kidney transplant, all the various elements involved in the process must be understood. It is important to know the characteristics of the donor organ, especially if the donor is older than 65. The histopathological features of the donor biopsy, especially its vascular status, are often related to an initial poor function of the transplanted kidney. The T lymphocyte inflammatory response is characteristic in acute cellular rejection; the degree of tubulitis, together with the amount of affected parenchyme, are important factors. The proportion of cellular sub-populations, such as plasma cells and macrophages, is also important, as they can be related to antibody-mediated humoral rejection. Immunofluorescent or immunohistochemical studies are necessary to rule out C4d deposits or immunogloblulins. The presence of abundant deposits of C4d in tubular basement membranes supports a diagnosis of humoral rejection, as does the presence of capillaritis, glomerulitis which, together with vasculitis, are typical diagnostic findings in C4d negative cases. Interstitial fibrosis, tubular atrophy and glomerular sclerosis, although non-specific, imply a chronic phase. Transplant glomerulopathy and multilamination in more than 6 layers of the tubular and glomerular basement membranes are quasi-specific characteristics of chronic humoral rejection. Electron microscopy is essential to identify of these pathologies as well as to demonstrate the presence of other glomerular renal diseases.

In Vivo Characteristics of Corneal Endothelium/Descemet Membrane Complex for the Diagnosis of Corneal Graft Rejection

PURPOSE

To evaluate the utility of endothelial/Descemet membrane complex (En/DM) characteristics in diagnosing corneal graft rejection.

DESIGN

Diagnostic reliability study.

METHODS

One hundred thirty-nine eyes (96 corneal grafts post penetrating keratoplasty or Descemet stripping automated endothelial keratoplasty: 40 clear, 23 actively rejecting, 24 rejected, and 9 nonimmunologic failed grafts; along with 43 age-matched control eyes) were imaged using high-definition optical coherence tomography. Images were used to describe En/DM and measure central corneal thickness (CCT) and central En/DM thickness (DMT). En/DM rejection index (DRI) was computed to detect the relative En/DM thickening to the entire cornea.

RESULTS

In actively rejecting grafts, DMT and DRI were significantly greater than controls and clear grafts (28, 17, and 17 μm and 1.5, 1 and 1, respectively; P < .001). Rejected grafts had the highest DMT and DRI compared to all groups (59 μm and 2.1; P < .001). DMT and DRI showed excellent accuracy, significantly better than that of CCT, in differentiating actively rejecting from clear grafts (100% and 96% sensitivity; 92.5% and 92.5% specificity), actively rejecting from rejected grafts (88% and 83% sensitivity; 91% and 83% specificity), and nonimmunologic failed from rejected grafts (100% and 100% sensitivity; 88% and 100% specificity). DMT correlated significantly with rejection severity (P < .001).

CONCLUSIONS

In corneal grafts, in vivo relative thickening of the En/DM is diagnostic of graft rejection as measured by DMT and DRI. These indices have excellent accuracy, sensitivity, and specificity in detecting graft immunologic status, superior to CCT. DMT is a quantitative index that correlates accurately with the severity of rejection.

Refinement of the criteria for ultrastructural peritubular capillary basement membrane multilayering in the diagnosis of chronic active/acute antibody-mediated rejection

Chronic active/acute antibody-mediated rejection (cABMR) is the main cause of late renal allograft loss. Severe peritubular capillary basement membrane multilayering (PTCML) assessed on electron microscopy is one diagnostic feature of cABMR according to the Banff 2013 classification. We aimed to refine the PTCML criteria for an earlier diagnosis of cABMR. We retrospectively investigated ultrastructural features of 159 consecutive renal allografts and 44 nonallografts. The presence of serum donor-specific antibodies at the time of biopsy of allografts was also examined. Forty-three patients (27.0%) fulfilled the criteria of cABMR, regardless of PTCML, and comprised the cABMR group. Forty-one patients (25.8%) did not exhibit cABMR features and comprised the non-cABMR allograft control group. In addition, 15 zero-day wedge resections and 29 native kidney biopsies comprised the nonallograft control group. When the diagnostic accuracies of various PTCML features were assessed using the cABMR and non-cABMR allograft control groups, ≥4 PTCML, either circumferential or partial, in ≥2 peritubular capillaries of the three most affected capillaries exhibited the highest AUC value (0.885), greater than the Banff 2013 classification (0.640). None of the nonallograft control groups exhibited PTCML features. We suggest that ≥4 PTCML in ≥2 peritubular capillaries of the three most affected cortical capillaries represents the proper cutoff for cABMR.

Interstitial fibrosis is the critical determinant of impaired renal function in transplant glomerulopathy

AIM

Transplant glomerulopathy (TG) is a feature of chronic antibody-mediated injury in the glomerular capillaries in renal transplant recipients. TG is generally associated with proteinuria; however, renal function at the diagnosis of TG varies. This study aimed to determine which morphological abnormalities are associated with renal function and proteinuria at the diagnosis of TG.

METHODS

A total of 871 renal transplantations were performed at Tokyo Women's Medical University between 2005 and 2013. TG was diagnosed in 127 biopsies from 58 (6.7%) recipients. Renal function was evaluated by the estimated glomerular filtration rate (eGFR). Proteinuria was assessed by a dipstick test: positive for +1 and over.

RESULTS

At diagnosis, of 127 biopsies, 72, 37, and 18 had mild, moderate, and severe TG (Banff cg). The severity of TG was not associated with decreased eGFR at the time of biopsy (cg1: 36.1 ± 14.8, cg2-3: 38.8 ± 14.5 mL/min per 1.73 m(2) , P = 0.25), whereas the severity of interstitial fibrosis (IF) (Banff ci) was significantly associated with decreased eGFR (ci0-1: 42.75 ± 13.32, ci2-3: 27.69 ± 11.94 mL/min per 1.73 m(2) , P < 0.0001). The multivariate analysis revealed that IF was the only independent risk factors for decreased eGFR (OR = 4.38, P = 0.0006). Meanwhile, TG was identified as the only independent risk factor for the incidence of proteinuria (OR = 2.67, P = 0.014).

CONCLUSION

Interstitial fibrosis was a critical determinant of impaired renal function at the diagnosis of TG. The severity of TG was significantly associated with proteinuria, but did not contribute to renal dysfunction.

Clinical and pathological analyses of interstitial fibrosis and tubular atrophy cases after kidney transplantation

AIM

We carried out a clinicopathological analysis of cases presenting with interstitial fibrosis and tubular atrophy (IF/TA) after renal transplantation in an attempt to clarify the mechanisms underlying the development and prognostic significance of IF/TA.

METHODS

IF/TA was diagnosed in 35 renal allograft biopsy specimens (BS) obtained from 35 renal transplant recipients under follow up at the Department of Transplant Surgery, Kidney Center, Toda Chuo General Hospital, between January 2014 and March 2015.

RESULTS

IF/TA was diagnosed at a median of 39.9 months after the transplantation. Among the 35 patients with IF/TA, 19 (54%) had a history of acute rejection. Among the 35 BS showing evidence of IF/TA, the IF/TA was grade I in 25, grade II in 9, and grade III in 1. Arteriosclerosis of the middle-sized arteries was observed in 30 BS (86%). We then classified the 35 BS showing evidence of IF/TA according to their overall histopathological features, as follows; IF/TA alone (6 BS; 17%), IF/TA + medullary ray injury (12 BS; 34%), and IF/TA + rejection (12 BS; 34%). Loss of the renal allograft occurred during the observation period in one of the patients (3%). Of the remaining patients with functioning grafts, deterioration of the renal allograft function after the biopsies occurred in 15 patients (43%).

CONCLUSIONS

The results of our study suggests that rejection contributes to IF/TA in 30-40% of cases, medullary ray injury in 30-40% of cases, and nonspecific injury in 20% of cases. IF/TA contributes significantly to deterioration of renal allograft function.

Current pathological perspectives on chronic rejection in renal allografts

Chronic rejection in renal transplantation clinically manifests as slow deterioration in allograft function and is a major contributor of late renal graft loss. Most cases of chronic rejection involve chronic antibody-mediated rejection (ABMR) triggered by the interaction of donor-specific alloantibodies with endothelial cells of the microcirculation. The evolution of the Banff classification involved a major revision of the ABMR criteria during the 2000s and led to the inclusion of detailed pathological characteristics of chronic ABMR in the 2013 Banff scheme, including microcirculation damage observed as newly formed basement membranes and arterial fibrous intimal proliferation. Inflammation of microvasculature including glomeruli and/or peritubular capillaries is also seen in substantial cases of chronic ABMR, defined as chronic active ABMR. Chronic active T cell-mediated rejection (TCMR) results from chronic T cell-mediated injury involving renal arteries but is less characterized under the current Banff classification, mainly due to the expanding histological criteria of chronic active ABMR. Characteristics shared by these two chronic rejection types can potentially cause diagnostic confusion. Hence, the diagnostic criteria or categories of chronic renal rejection require amendment of the current Banff classification. Assessment of rejection cases with molecular phenotyping advanced the mechanistic understanding of various dysfunctions in renal allograft, including ABMR and TCMR. Identification of disease-specific changes in gene expression by immunohistological studies, especially in chronic ABMR, has already been validated by several studies, warranting potential application to the pathological diagnostic process. This review provides an overview of current pathological perspectives on chronic rejection of renal allografts and future directions.

Clinical and pathological analyses of transplant glomerulopathy cases

AIM

Transplant glomerulopathy (TG) is included as one of the criteria of chronic active antibody-mediated rejection (c-AMR) in Banff 09 classification. In this report, we discuss the clinical and pathological analyses of cases of TG after renal transplantation.

PATIENTS

TG was diagnosed in 86 renal allograft biopsy specimens (BS) obtained from 50 renal transplant patients followed up at our institute between January 2006 and October 2012. We retrospectively reviewed the data of these 86 BS and 50 patients.

RESULTS

Among the 50 patients, 42 (84%) had a history of acute rejection (AR); of these, 30 (60%) had acute antibody-mediated rejection (a-AMR). Among the 86 BS of TG, the TG was mild in 35 cases (cg1 in Banff classification), moderate in 28 cases (cg2) and severe in 23 cases (cg3). Peritubular capillaritis was present in 74 BS (86%), transplant glomerulitis in 65 (76%), interstitial fibrosis and tubular atrophy (IF/TA) in 71 (83%), thickening of the peritubular capillary (PTC) basement membrane in 72 (84%), and interstitial inflammation in 40 (47%). C4d deposition in the PTC was present in 49 BS (57%); 39 of these 49 BS showed diffuse C4d deposits in the PTC (C4d3), while the remaining 10 BS showed focal deposits (C4d2). Diffuse C4d deposition in the glomerular capillaries (GC) was seen in 70 BS (81%), while focal C4d deposition in the GC was seen in 9 (11%). In the assay using plastic beads coated with HLA antigen performed in 67 serum samples obtained in the peri-biopsy period, circulating ant-HLA alloantibody was detected in 55 (82%); in 33 of the 55 (49%) samples, donor-specific antibodies (DSA) were detected. Among our study, the findings in 22 BS (26%) fully met the criteria for c-AMR in Banff '09 classification, including TG, C4d deposition in the PTC and presence of DSA, while those in 27 BS were suspicious of c-AMR. Deterioration of the renal allograft function after the biopsies was seen in 31 patients (62%), of which 11 lost their graft.

CONCLUSIONS

We suggest that histopathological changes of transplant glomerulopathy might be accompanied by inflammation of the microvasculature, such as transplant glomerulitis and peritubular capillaritis, thickening of the peritubular capillary basement membrane, and circulating anti-HLA antibodies. C4d deposition in the PTC is not always present in biopsy specimens of TG. We speculated that C4d deposition in the GC, rather than that in the PTC might be a more characteristic manifestation of TG. Many of the patients with TG had a history of AR. Anti-HLA antibody Class II, particularly when the antibody was DSA Class II, appeared to be associated with the development of TG. The prognosis of grafts exhibiting TG was not too good even under the currently used immunosuppressive protocol.

Reviews on mysterious vascular endothelial cells in renal allografts

Endothelial cells (ECs) are involved in allograft rejection and are prime targets, but also key players. HLA antigens are the most prominent targets of alloantibodies in transplantation. Alloantibodies against other antigens such as ABO blood group antigens and non-HLA antigens could also be demonstrated. Alloantibodies undoubtedly cause allograft rejection. Activation of ECs by anti-EC antibodies and direct antibody- or complement mediated EC damage may be suggested. However, the mechanisms underlying acute antibody-mediated rejection (AAMR) and chronic rejection (CR) remain unclear. In this review, the relationship between vascular endothelium and rejection is discussed mainly from our reports, and the mechanism and pathogenesis of CR are discussed.

Diagnostic significance of peritubular capillary basement membrane multilaminations in kidney allografts: old concepts revisited

BACKGROUND

Injury to peritubular capillaries and capillary basement membrane multilamination (PTCL) is a hallmark of antibody-mediated chronic renal allograft rejection. However, the predictive diagnostic value of PTCL is incompletely studied.

METHODS

We analyzed the diagnostic significance of PTCL and propose diagnostic strategies. We evaluated 360 diagnostic native and 187 transplant kidney specimens by electron microscopy (terminology: PTCL-C, severe; PTCL subgroup C3, very severe multilamination; see Materials and Methods for definitions).

RESULTS

PTCL was not pathognomonic for any specific disease. PTCL-C/C3 was rare in native kidneys (C, 6%; C3, 1%), associated mainly with late thrombotic microangiopathy (C: 78%; C3: 11% of cases). In allografts, PTCL-C/C3 was significantly more common, especially in specimens more than 24 months after transplantation (C, 47%; C3, 31%). PTCL-C/C3 was found in acute (C, 20%; C3, 7%) and chronic T-cell rejection (C, 67%; C3, 29%), calcineurin inhibitor toxicity (C, 36%; C3, 18%), or C4d(+) specimens (C, 61%; C3, 50%) with odds ratios between 4 and 36. PTCL-C3 was more predominant in cases with antibody-mediated injury. Highest odds ratios (81-117) for PTCL-C/C3 were noted in combined injuries, that is, mixed chronic T-cell and concurrent chronic antibody-mediated rejection. Positive predictive values of PTCL-C and C3 are the following: all rejection types, 89% and 93%; all Banff chronic rejection types, 69% and 71%; and chronic presumptive antibody rejection, 37% and 49%, respectively. Corresponding negative predictive values of C and C3 for different Banff rejection categories are between 50% and 94%.

CONCLUSIONS

The presence of PTCL-C3 is a helpful adjunct finding to diagnose rejection-induced tissue injury but cannot precisely predict the Banff rejection category. Conversely, the absence of PTCL-C3 is helpful in excluding chronic, Banff category II antibody-mediated rejection.

Human leukocyte antigen antibody incompatible renal transplantation

Anti-human leukocyte antigen (HLA) antibodies are recognized as an important problem in organ transplant recipients. This is because antibodies formed against a graft months or years after implantations are the major cause of late allograft failure, and also because protocols allow the transplantation of some grafts across pre-formed HLA antibodies. Advances in our understanding of anti-HLA antibody- mediated rejection (AMR) have occurred because of a better understanding of the histological findings during AMR; more sensitive and specific methods to measure anti-HLA antibodies; and through clinical investigation of patients transplanted across an HLA barrier. Despite advances in therapy and investigation, AMR remains a major problem and treatment protocols often fail to treat it successfully. This review aims to describe the issues in each of these areas and to suggest how clinicians may be able to improve the management of patients with anti-HLA antibodies.

Current problems of chronic active antibody-mediated rejection

The Banff 2007 classification allows chronic rejection to be differentiated based on clinicopathological characteristics evidenced by two independent immunologic mechanisms; chronic active antibody-mediated rejection and chronic active T-lymphocyte mediated rejection. However, several incompletely understood issues concerning chronic active antibody-mediated rejection remain. Chronic active antibody-mediated rejection is characterized by C4d deposition in the capillary basement membrane(PTC), the presence of circulating anti-donor antibodies(DSA), and morphologic evidence of chronic tissue injury such as glomerular double contours compatible with transplant glomerulopathy (TPG), PTC basement membrane multilayering, interstitial fibrosis/tubular atrophy, and fibrous arterial intimal thickening. PTC basement membrane multilayering correlates highly with TPG, and most of TPG have evidence of either C4d-positive staining or DSA. However, the proposed criteria do not apply to all situations of chronic active antibody-mediated rejection. C4d is not a magic marker for antibody-mediated rejection. C4d staining is not always highly sensitive for detecting antibody-mediated rejection. Multi-institutional studies should be conducted to better understand the clinicopathological context of chronic antibody-mediated rejection. These studies should include well-designed serial protocol biopsies with evaluation by electron microscopy, C4d staining performed on frozen sections, and assessment using sensitive DSA detection methods.

De novo membranous nephropathy and antibody-mediated rejection in transplanted kidney

BACKGROUND

The etiology of de novo membranous nephropathy (MN) after kidney transplantation is still uncertain. Immunological response to various allograft antigens is speculated to be a candidate for the etiology.

METHODS

Seventeen patients with post-transplant de novo MN were studied clinically and pathologically in comparison with control post-transplant patients without MN. Double immunofluorescent staining was performed to identify the presence of donor-specific human leukocyte antigen (HLA) combined with IgG in the deposits on glomerular capillary walls.

RESULTS

De novo MN occurs in relatively late period after transplantation (102.1 ± 68.3 months), presenting various degree of proteinuria. Histological findings associated with antibody-mediated rejection (AMR), such as peritubular capillaritis and C4d deposition in peritubular capillary, were more frequently observed in the patients with de novo MN than the non-MN control patients. Donor-specific antibody (DSA) was detected in five patients at the time of biopsy. In one case of de novo MN with DSA, a donor-derived HLA was identified in the subepithelial deposits on the glomerular capillary walls combined with IgG deposition.

CONCLUSIONS

DSA and AMR might play some roles for the pathogenesis in some patients with de novo MN after kidney transplantation.

Decrease of blood type antigenicity over the long-term after ABO-incompatible kidney transplantation

BACKGROUND

Few studies have investigated the changes in the antigenicities of the transplanted organs after transplantation.

METHODS

We examined, by immunohistochemical assay, the changes in expression of the blood-type antigens on the transplanted kidneys over the long-term after ABO-incompatible kidney transplantation with A- or B-antigen incompatibility (blood type A to B and B to A). The subjects were six patients, including one case with graft loss, who had received ABO-incompatible kidney allografts more than ten years previously. As normal controls, four cases of ABO-compatible transplantation during the same period, including two recipient/donor pairs each with blood group A1 and blood group B were enrolled.

RESULTS

Expression of the blood-type A or B antigens decreased gradually to 91.8% during the first three months after transplantation, 85.8% during the first five years, 64.1% during the first ten years, and 57.6% over ten years after transplantation on average in ABO-incompatible transplant recipients. In one patient with graft loss due to severe antibody-mediated rejection, the donor's type B blood-type antigens on the transplanted graft had changed but partially to the recipient's blood-type A antigen by 2582days after the transplantation, suggestive of the occurrence of blood-type chimerism on the endothelium. In ABO-compatible transplant recipients, such changes in expression were not observed. The average percentage of blood-type antigen-positive vessels at more than ten years after the renal transplantation was 99.8%.

CONCLUSIONS

Decrease in the expression of the donor's blood-type antigen on the endothelium of the graft has been considered as one of the mechanisms underlying the accommodation occurring over the long-term after ABO-incompatible kidney transplantation. On the other hand, establishment of antigenic chimerism on the graft endothelium could be one of the hallmarks of the immunological reaction associated with antibody-mediated rejection.

Segmentation and thickness measurement of glomerular basement membranes from electron microscopy images

An algorithm for segmentation and thickness measurement of the glomerular basement membranes (GBM) in electron microscopy kidney images is presented. Differences in intensities and variations between GBM and other components in the image are employed. Regions of extreme intensities such as the black area of blood cells and white areas of urinary spaces are pre-excluded. Areas of sharp edges are either at the GBM borders or unrelated to GBM regions. These non-GBM sharp edges, along with the pre-excluded regions, are used as barriers limiting the size of the fitting circles centered at a location in the image domain to form a two-dimensional function, proportional to the radius of the largest fitting circle, at the location. A local peak in the radius function corresponds to the largest circle in the local area. The set of the combined peaks in two perpendicular directions is calculated before a thinning procedure is applied. After removing the unwanted branches, a centerline of the GBM is produced. The segmentation of the GBM is then straightforward from expanding each point in the centerline to a circle of radius defined by the radius function. The average of the diameters of the circles gives the average GBM thickness. Results of the real GBM images are provided. Visual comparisons from the superimposed GBM boundaries show that the algorithm provides accurate GBM segmentation. The evaluations of the average GBM thicknesses are also compared to those from the manual tracing method.

A semi-automatic algorithm for measurement of basement membrane thickness in kidneys in electron microscopy images

In this paper, we present a semi-automatic algorithm for measurement of the glomerular basement membrane thickness in electron microscopy kidney images. A string of sparsely spaced points are manually inputted along the central line of the basement membrane (lamina densa) to be measured. The gaps between successive input points are lineally interpolated. A nonlinear mapping is applied to straighten the curved central line. Two distance functions of edges to the central line are constructed. The smooth envelope lines are obtained by repetitive applications of a linear low-pass filtering followed by a comparing and selecting process. The boundaries of the glomerular basement membrane are obtained from the inverse mapping of the envelope functions. The average basement membrane thickness is estimated as the ratio of the basement membrane area to the length of the central line.

Caveolin-1 expression is a distinct feature of chronic rejection-induced transplant capillaropathy

Peritubular capillary basement membrane multilayering (PTCBMML) is a pathological landmark of chronic rejection-induced transplant capillaropathy (TC), but its cellular mechanisms are not fully understood. We observed de novo caveolae formation in endothelial cells in TC under electron microscopy. To examine the role of caveolae and their structural components in TC, biopsy samples from cases of chronic rejection were double-immunostained for Caveolin-1 (Cav-1) and Pathologische Anatomie Leiden-endothelium (PAL-E; a marker of peritubular capillary [PC]). Thirty-two cases of chronic rejection (group I) were compared with 18 cases of interstitial fibrosis and tubular atrophy with no evidence of any specific etiology (IF/TA; group II) and eight cases of peritubular capillaritis (group III). The Cav-1/PAL-E immunoreactivities in groups I-III (%Cav-1/PAL-E) were 41.8+/-23.1%, 8.1+/-7.3% (p < 0.01 vs. group I) and 12.7+/-7.4% (p < 0.01 vs. group I), respectively. Furthermore, multiple linear regression models demonstrated that %Cav-1/PAL-E was independently associated with the PTCBMML grade and reduced PC number. No correlation was observed between %Cav-1/PAL-E and PC C4d deposition in group I. We conclude that de novo caveolae formation in PC endothelia is involved in TC in chronic rejection.

Chronic allograft nephropathy

PURPOSE OF REVIEW

Despite dramatic declines in acute rejection and early graft failure, long-term outcomes after kidney transplantation have improved little during the past 25 years. Most late allograft failure is attributed to chronic allograft nephropathy, but this is a clinicopathological description and not a diagnosis, and its pathogenesis and treatment are largely unknown.

RECENT FINDINGS

Recent studies suggest that acute rejection during the first few months, and calcineurin inhibitor toxicity thereafter, may both contribute to chronic allograft nephropathy. There is also accumulating evidence that injury from antibody-mediated rejection may play an important pathogenic role in at least some patients with chronic allograft nephropathy, particularly those with transplant glomerulopathy. Therapeutic measures, including protocols to reduce calcineurin inhibitor exposure, remain largely unproven.

SUMMARY

Understanding why so many kidney allografts fail, despite effective preventive measures for early acute rejection, is one of the most important areas of research in kidney transplantation today.

Peritubular capillaritis in renal allografts: prevalence, scoring system, reproducibility and clinicopathological correlates

While glomerulitis is graded according to the Banff classification, no criteria for scoring peritubular capillaritis (PTC) have been established. We retrospectively applied PTC-scoring criteria to 688 renal allograft (46 preimplantation, 461 protocol, 181 indication) biopsies. A total of 26.3% of all analyzed biopsies had peritubular capillaritis (implant 0%, protocol 17.6%, indication 45.5%; p < 0.0001). The most common capillaritis pattern was of moderate severity (5-10 luminal cells), focal in extent (10-50% of PTC), with a minority of neutrophils. A total of 24% of C4d- compared with 75% of C4d+ biopsies showed capillaritis (p < 0.0001). More than 80% of biopsies with glomerulitis had peritubular capillaritis. A total of 50.4% of biopsies with borderline or T-cell mediated rejection (TCMR) and 14.1% of biopsies without TCMR or antibody-mediated rejection (ABMR) showed capillaritis (p < 0.0001). The inter-observer reproducibility of the PTC-scoring features was fair to moderate. Diffuse capillaritis detected in early protocol biopsies had significant negative prognostic impact in terms of glomerular filtration rate 2 years posttransplantation. Indication biopsies show a significantly higher prevalence of capillaritis than protocol biopsies (45.5% vs. 17.6%; p < 0.0001). Capillaritis is more frequent and pronounced in ABMR, but can be observed in TCMR cases. Thus, scoring of peritubular capillaritis is feasible and can provide prognostic and diagnostic information in renal allograft biopsies.