*Purpose: Chronic active antibody-mediated rejection (c-aABMR) is an intermediate process in the development of chronic antibody-mediated rejection (c-ABMR), a key problem in the long-term failure of kidney graft. PC3-secreted microprotein (PSMP), a new chemotactic cytokine recruiting macrophages, enhances fibrosis progression. However, the relationship between PSMP and chronic active antibody-mediated rejection (c-aABMR) in kidney transplantation need to be further explored. This study was to investigate the role PSMP playing on the progression of c-aABMR and c-ABMR.

*Methods: In this study, a total of 29 kidney transplant recipients were included and classified into chronic active antibody-mediated rejection (c-aABMR) group (n=14), chronic antibody-mediated rejection (c-ABMR) group (n=5) and normal function group (n=10) according to their allograft biopsy pathology diagnosis. Patients demographics, kidney allograft biopsy sample fibrosis stained with HE and masson, immunohistochemistry staining of PSMP and CD68, PSMP gene-expression quantitated by real time RT-PCR and the serum and urine PSMP level were compared between three groups. The serum and urine PSMP expressions were detected by ELISA.

*Results: Patients demographics results of three groups were no difference. Compared with normal groups, the allograft survival rate of c-aABMR group was significantly low (58.3% vs. 0%). Pathologic Banff scrores of three groups showed that c-aABMR group had more severe peritubular capillaritis (PTC) and tubulitis inflammation (t). Moreover,there was more fibrosis area and eGFR declined in both c-aABMR and c-ABMR groups, but no difference between the two groups. While CD68 expression was highest in c-aABMR among three groups, which was significantly positive associated with fibrosis grade in c-aABMR. Consistent with the CD68 expression, PSMP expression was significance higher in c-aABMR group than c-ABMR and normal groups. A significant correlation was found between the expression between CD68 and PSMP in c-aABMR, PSMP high expressed grafts had significantly higher t, i, c4d score and more allograft function loss compared to PSMP low expressed grafts. In addition, we found that urinary PSMP may be a candidate molecule marker for c-aABMR. Indeed, urinary PSMP concentration was significantly higher in kidney grafts pathologically diagnosed with c-aABMR than c-ABMR and normal counterparts, while no clear trend in serum. Indeed, urinary PSMP concentration was significantly higher in kidney grafts pathologically diagnosed with c-aABMR than c-ABMR and normal counterparts, while no clear trend in serum.

*Conclusions: PSMP level was associated with macrophages infiltrating and fibrosis in c-aABMR which could be a promising biomarker to distinguish and predict risks of c-aABMR allograft lost.

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