Improvements in immunosuppression have reduced acute kidney allograft rejection and clinicians are now seeking ways to prolong allograft survival to 20 years and beyond. The primary cause of kidney allograft loss is still chronic rejection, followed by death with a functioning allograft and primary kidney disease recurrence. Thus, overcoming kidney allograft rejection remains the most important issue. Kidney allograft rejection can be classified into two types: T cell-and antibody-mediated rejection. Both are diagnosed pathologically based on the Banff 2013 classification. Other important pathological features in addition to rejection include calcineurin inhibitor toxicity, polyomavirus nephropathy, and recurrence of the primary kidney disease. Here, we review the diagnosis and representative features of histopathological findings in transplanted kidneys.

Background Both immunological and non‐immunological etiologies affect graft function after kidney transplantation, including acute rejection, calcineurin inhibitor toxicity, and a recurrence of glomerulonephritis. Glomerular enlargement or glomerular sclerosis due to glomerular hyperfiltration related to increased renal blood flow is another cause. Although the glomerular volume in baseline biopsies predicts late allograft function, the relationship between allograft function and the annual changes in glomerular volume after kidney transplantation are unclear. Aim We investigated changes in glomerular volume after kidney transplantation and their clinicopathological relationship. Methods We enrolled 23 patients with stable kidney function without an episode of rejection or any complication resulting in a functional decrease in the graft. We measured glomerular volume (GV) using the Weibel–Gomez method and glomerular density (GD) using 0,1 h biopsy samples as baseline controls and 1 yr biopsy samples and investigated the association between the changes in them and clinical parameters, including graft function, proteinuria, and renal hemodynamic markers, including effective renal plasma flow (ERPF) and filtration fraction (FF). The ERPF was calculated from a 99mTc‐mercaptoacetyltriglycine (MAG3) renogram. Results The GV and ERPF increased significantly 1 yr after kidney transplantation. In contrast, proteinuria decreased significantly and Δproteinuria (1 yr – 1 month after transplantation) was correlated with ΔGV (P < 0.05, rs = –0.467). Conclusion Glomerular enlargement 1 yr after transplantation may be related to improved proteinuria. It is possible that glomerular enlargement serves as a renal adaptation after kidney transplantation.

Background: Recurrence of IgA nephropathy (IgAN) in the transplanted kidney is associated with graft survival, but no specific treatment is available. Tonsillectomy (TE) reportedly arrests the progression of IgAN in the native kidney. Thus, we conducted a single-center retrospective cohort study to evaluate the effect of TE prior to IgAN recurrence. Methods: Of the 36 patients with biopsy-proven IgAN who underwent kidney transplantation, 27 were included in this study. Nine patients underwent TE at 1 year after kidney transplantation (group 1), and the remaining 18 did not undergo TE (group 2). Results: The rate of histological IgAN recurrence was significantly lower in group 1 than in group 2 (11.1 vs. 55.6%, log-rank p = 0.046). In addition, half of the recurrent patients in group 2 exhibited active lesions, compared to none in group 1. Serum Gd-IgA1 levels decreased after TE in group 1, whereas they remained stable or increased slightly in group 2. In the recurrent cases, IgA and Gd-IgA1 were found in the germinal center in addition to the mantle zone of tonsils. Finally, mesangial IgA and Gd-IgA1 immunoreactivity was reduced after TE in some cases. Conclusion: Our data suggest that TE at 1 year after kidney transplantation might be associated with the reduced rate of histological IgAN recurrence. TE arrested or reduced serum Gd-IgA1 and mesangial Gd-IgA1 immunoreactivity. Therefore, we generated a hypothesis that serum Gd-IgA1 derived from the tonsils may play a pivotal role in the pathogenesis of IgAN. Based on these findings, we need to conduct verification in a prospective randomized controlled trial.

ABSTRACT:We report a case of plasma cell-rich rejection accompanied by acute antibody-mediated rejection in a patient with ABO-incompatible kidney transplantation. A 33-year-old man was admitted for an episode biopsy; he had a serum creatinine (S-Cr) level of 5.7 mg/dL 1 year following primary kidney transplantation. Histological features included two distinct entities: (1) a focal, aggressive tubulointerstitial inflammatory cell (predominantly plasma cells) infiltration with moderate tubulitis; and (2) inflammatory cell infiltration (including neutrophils) in peritubular capillaries. Substantial laboratory examination showed that the patient had donor-specific antibodies for DQ4 and DQ6. Considering both the histological and laboratory findings, we diagnosed him with plasma cell-rich rejection accompanied by acute antibody-mediated rejection. We started 3 days of consecutive steroid pulse therapy three times every 2 weeks for the former and plasma exchange with intravenous immunoglobulin (IVIG) for the latter histological feature. One month after treatment, a second allograft biopsy showed excellent responses to treatment for plasma cell-rich rejection, but moderate, acute antibody-mediated rejection remained. Therefore, we added plasma exchange with IVIG again. After treatment, allograft function was stable, with an S-Cr level of 2.8 mg/dL. This case report demonstrates the difficulty of the diagnosis of, and treatment for, plasma cell-rich rejection accompanied by acute antibody-mediated rejection in a patient with ABOincompatible kidney transplantation. We also include a review of the related literature.Both plasma cell-rich rejection (PCAR) and acute antibodymediated rejection (AMR) remain refractory rejection entities in spite of the recent development and establishment of immunosuppressive therapy. The former is characterized by the presence of mature plasma cells that comprise more than 10% of the inflammatory cell infiltration in a renal allograft.1 PCAR is a rare type of rejection noted in approximately 5-14% of patients with biopsy-proven acute rejection, but graft survival is poor and standard therapeutic options have yet to be generally established.2 The latter is a well-recognized type of rejection that is due in large part to antibodies to human leukocyte antigen (HLA) alleles. Recent studies have focused on not only HLA-DR compatibility, but also on that of HLA-DQ, since de novo DQ donor-specific antibodies (DSAbs) are the predominant HLA class II DSAbs found after transplantation. 3 We report here a refractory case of PCAR accompanied by AMR due to de novo DQ DSAbs 1 year after ABOincompatible, living-related kidney transplantation. CASE REPORTA 33-year-old Japanese man was admitted to our hospital for an episode biopsy 1 year following primary kidney transplantation. He was diagnosed with IgA nephropathy at the age of 31 years and received a living-related kidney transplantation at the age of 32 from his mother. ABO blood types were incompatible, and HLA alleles were mismatched at two bs_bs_ban...

The low sensitivity of C4d immunoreactivity in peritubular capillaries (PTCs) hinders its use in the diagnosis of chronic active antibody-mediated rejection (CAAMR). C4d-negative CAAMR was defined in the 2013 Banff classification, which included the expression of endothelial-associated transcripts (ENDATs). We previously showed that the ENDAT caveolin-1 (CAV-1) is a distinct feature of CAAMR. In this study, we investigated the prognostic value of CAV-1 immunoreactivity in PTCs in kidney transplant patients. Ninety-eight kidney transplant recipients were included in this study. The prognostic value of CAV-1 immunoreactivity in PTCs was evaluated by double immunostaining for CAV-1 and pathologische Anatomie Leiden endothelium (PAL-E, a PTC marker) in the PTCs of kidney allograft biopsy samples. The patients were divided into two groups: CAV-1/PAL-E<50% and CAV-1/PAL-E≥50%. Kaplan-Meier curves showed that CAV-1/PAL-E≥50% patients had a significantly worse prognosis than that of CAV-1/PAL-E<50% patients (log-rank; P<.001). C4d staining of PTCs was not associated with the development of graft failure (log-rank; P=.345), whereas in a multivariate Cox regression analysis, CAV-1 immunoreactivity in PTCs was independently associated with graft failure (hazard ratio: 11.1; P=.0324). CAV-1 immunoreactivity in PTCs may serve as a prognostic marker for kidney allograft survival.

Background Previous studies have shown that a donor/recipient body weight mismatch affects long‐term graft survival and graft function after kidney transplantation. However, the mechanisms are not fully understood. Aim To address the mechanisms, we compared the pathological and physiological features between patients with a donor/recipient body weight mismatch and those without a mismatch 1 yr after kidney transplantation. Furthermore, we investigated the correlation with the donor/recipient body weight ratio. Methods We examined allograft biopsy specimens from 10 recipients with stable kidney function, with body weight mismatch (donor/recipient body weight ratio [D/R BWR] < 0.9), and compared them with samples from 13 patients without mismatch. We measured glomerular volume (GV) using the Weibel–Gomez method and glomerular density (GD) defined by nonsclerotic glomerular number/renal cortical area as pathological findings. The physiological parameters included estimated glomerular filtration rate and proteinuria (mg/day). These data were evaluated to identify a correlation with D/R BWR. Results The pathological features showed that GV and GD were identical in the two groups. However, when glomerular enlargement was defined by ΔGV (GV at the 1‐yr biopsy minus GV at baseline biopsy), ΔGV was higher in mismatch cases compared with that in cases without a mismatch (10.6 ± 4.6 vs. 5.5 ± 7.1 × 105 μm3; P = 0.049). Furthermore, D/R BWR was significantly correlated with ΔGV (P = 0.03, r = –0.436). eGFR values were physiologically identical between the two groups, but the mismatch cases had significantly higher proteinuria levels than that of the cases without a mismatch at 1 yr after kidney transplantation. Conclusion A donor/recipient body weight mismatch could affect glomerular enlargement and increased proteinuria 1 yr after kidney transplantation. How these two features affect long‐term graft survival and function must be addressed in the future.

ABSTRACT:A 56-year-old man who had undergone cadaveric kidney transplantation 21 months earlier was admitted to our hospital for a protocol biopsy; he had a serum creatinine level of 1.2 mg/dL and no proteinuria. Histological features showed two distinct entities: (i) inflammatory cell infiltration, in the glomerular and peritubular capillaries and (ii) focal, aggressive tubulointerstitial inflammatory cell infiltration, predominantly plasma cells, with mild tubulitis (Banff 13 classification: i2, t1, g2, ptc2, v0, ci1, ct1, cg0, cv0). Immunohistological studies showed mildly positive C4d immunoreactivity in the peritubular capillaries. The patient had donor specific antibody to human-leucocyte-antigen-DR53. We diagnosed him with subclinical antibody-mediated rejection accompanied by plasma cell-rich acute rejection. Both antibody-mediated rejection due to anti-human-leucocyteantigen -DR53 antibodies and plasma cell-rich acute rejection are known to be refractory and have a poor prognosis. Thus, we started plasma exchange with intravenous immunoglobulin and rituximab for the former and 3 days of consecutive steroid pulse therapy for the latter. Three months after treatment, a follow-up allograft biopsy showed excellent responses to treatment for both histological features. This case report considers the importance of an early diagnosis and appropriate intervention for subclinical antibody-mediated rejection due to donor specific antibody to humanleucocyte-antigen-DR53 and plasma cell-rich acute rejection.A recent study demonstrated that untreated subclinical antibody-mediated rejection (ABMR) is an important predictor of poor allograft outcomes.

Background Helicobacter cinaedi causes bacteremia and cellulitis, mainly in immunocompromised patients. We report a rare case of H. cinaedi bacteremia with cellulitis in a living-donor kidney transplant recipient identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS).Case summaryA 54-year-old Asian man with IgA nephropathy underwent living-donor kidney transplantation 14 years previously. He was admitted to our hospital for evaluation of fever and multifocal cellulitis. H. cinaedi was isolated and identified from the patient’s blood using matrix-assisted laser desorption ionization time-of-flight mass spectrometry and gyrase subunit B-targeted polymerase chain reaction assays. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry has proven over the years to be a rapid and accurate universal method for the identification of microorganisms.ConclusionsThe combined use of these detection methods enabled the appropriate administration of 6 weeks of antibiotic therapy. The patient recovered completely, with no recurrence.