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It is unclear whether all donor-specific antibodies (DSA) can cause chronic antibody-mediated rejection (AMR). Subclinical stage before manifestation of renal dysfunction may be a critical period for reversing AMR. The aim of our study was to identify factors related to the development of subclinical AMR and to clarify the characteristics of de novo DSA.Eight hundred ninety-nine renal transplants were screened for HLA antibody. De novo DSA were detected in 95 patients. Forty-three patients without renal dysfunction who underwent renal biopsies were enrolled in this study. Eighteen patients (41.9%) were diagnosed with biopsy-proven subclinical AMR and treated with plasmapheresis and rituximab-based therapy, whereas 25 showed no findings of AMR.Significant subclinical AMR-related factors were younger recipients, history of acute T cell-mediated rejection and DSA class II, especially DR-associated DSA. Mean fluorescence intensity (MFI) values of DR-DSA were significantly higher, whereas DQ-DSA was not different between subclinical AMR and no AMR. The ΔMFI (50%), DSA-MFI values greater than 3000, and C1q binding DSA were also significant subclinical AMR-related factors (P0.05). Among 18 patients treated for subclinical AMR, 8 patients (44.4%) obtained over 50% reduction of DSA-MFI and/or improvement or no deterioration of pathological findings. In contrast, 25 patients without subclinical AMR did not show renal dysfunction clinically. Moreover, all of the 8 patients with rebiopsy after 2 years continued to demonstrate no AMR.About 40% of patients with de novo DSA demonstrated biopsy-proven subclinical AMR, leading to progressive graft injury. To validate the intervention and treatment for de novo DSA-positive patients without renal dysfunction, further study is necessary.

Background. Regulatory T cells (Tregs) have been suggested to be deeply associated with immune tolerance and long-term graft survival in transplantation. Some recipients with stable graft function (ST) could possibly minimize immunosuppression during the maintenance period. However, effective assays for assessing the suitability of patients have yet to be established. The purpose of this study was to elucidate the clinical relevance of Treg-related gene expression such as forkhead box P3 (Foxp3) in peripheral blood after renal transplantation. Methods. Several key molecules related to the function of immune cells such as Treg, including Foxp3, transforming growth factor-β, cytotoxic T-lymphocyte antigen-4, chemokine receptor 7, toll-like receptor 4, granzyme B, T-bet, GATA3, RORC, α 1,2 -mannosidase, and proteasome subunit β 10 were examined in the peripheral blood of 272 renal transplant recipients by quantitative real-time reverse-transcriptase polymerase chain reaction. The expression levels were compared between recipients with chronic rejection and ST. Results. Foxp3 messenger RNA (mRNA) levels were reduced immediately after transplantation and gradually recovered. Pretransplantation levels were closely correlated with 1 year posttransplantation levels. Recipients with chronic rejection had significantly lower levels of Foxp3, chemokine receptor 7, and granzyme B mRNA, and higher levels of toll-like receptor 4 and proteasome subunit β 10 mRNA compared with those with ST, although Foxp3 was the most relevant marker. Conclusion. There is a possibility that monitoring mRNA expression levels of Treg-related molecules in peripheral blood might offer useful information on patient selection and early detection of rejection when immunosuppression minimization strategy is implemented in renal transplantation.

Acute humoral rejection (AHR) is the most important risk factor for early graft loss in ABO-incompatible (ABO-i) kidney transplantation (RTx). The pathogenesis and diagnostic criteria for AHR after ABO-i RTx remain unclear. Complement fragment C4d deposition in peritubular capillaries (PTC), which is a sensitive indicator for activation of the classical complement pathway, was studied to establish the pathologic diagnostic indicator of AHR.Forty-four graft biopsy specimens from 19 patients with ABO-i living donors were analyzed within 90 days after RTx. Nineteen biopsy specimens with acute rejection after ABO-compatible (ABO-c) living-related RTx were used as controls. Diffuse and bright C4d deposition in PTC was considered significantly positive.All of 8 recipients with AHR showed significantly positive C4d in PTC in the ABO-i group, but 9 of 11 recipients without AHR were negative. In the ABO-c RTx group, 16 of 19 recipients were negative for C4d in PTC. The prevalence of C4d in PTC was significantly higher in ABO-i RTx (P0.05).C4d deposition is valuable as a specific and sensitive indicator for AHR, even of mild severity, in ABO-i RTx.