Evaluation of the relationship between chronic rejection and regulatory B cells in renal transplant recipients

Chronic kidney disease (CKD) is a common and important health problem which is affecting the world and requires appropriate treatment. End stage renal disease (ESRD) refers to the stage in which renal functions are insufficient to maintain vital functions and when renal replacement therapies are needed. Although renal transplantation is an elite method in most of the ESRD cases, some patients are confronted with as chronic allograft nephropathy (CAN) which is difficult in both diagnosis and treatment. Clinical and histopathological evidences are needed for diagnosis of CAN. Chronic rejection, which is the most important etiologic factor for CAN, is the result of immune system's response against allograft tissue. Although the immune physiopathology of chronic rejection has not yet been fully clarified, donor specific antibodies (DSA) synthesized from B cells have been shown to have a pathological role in the process of chronic rejection. As well as antibody synthesis and antigen presenting properties of B cells, inhibitor effects on the immune response of regulatory B cells (Breg) which is a B cell subset has been attracted attention on studies recently. Studies have shown that Bregs may play an active role in autoimmune events, cancer immunobiology, infections and transplant tolerance. The development stages, functions and clinical significance of Bregs have not been fully clarified yet. The aim of this study was to investigate the relationship between Breg subtypes (immature / transitional B cell, plasmablastic cell, B10 cell and BR1 cell) and chronic rejection within demographic, clinical and laboratory characteristics. Between 2016-2019, 45 patients over the age of 18 who were admitted to the Organ Transplantation Clinic of Akdeniz University Medical Faculty Hospital were included in the study. Twenty three patients who were interpreted as chronic rejection after biopsy with clinical indications, were included in the chronic rejection (CR) group. Eleven patients with stable renal function were included in the patient control (PC) group and eleven volunteers without any known disease were included in the healthy control (HC) group. Venous blood sample were taken from all the groups and immature/transitional B cell (CD19+CD24+CD38+), plasmablastic cell (CD19+24+38+27+), B10 cell (CD24+CD27+), BR1 cell (CD19+25+CD71+CD73-) levels were studied by flow cytometry, according to the ratio of total lymphocyte population. During the period in which the blood samples were taken, the patients' pre-transplant information and current information were recorded by using the hospital information management system MIA-MED and organ transplantation follow-up files. There was no significant difference between three groups in terms of demographic data such as age and gender. There was no significant difference between CR and PC groups in terms of immunological risk profiles such as PRA-1 and PRA-2 levels, missmatch count, transplantation history in the past and donor characteristics. Immature/transitional B cell levels were higher in the CR group [10,00 (2,40-34,80)], when compared to both PC group [7,50 (1,80-57,90)] and HC group [6,90 (3,80-14,00)] but the differences between each group were not significant (p>0.05). Plasmablastic B cell levels were higher in the CR group [7,80 (2,10-27,40)] when compared to the other groups. The difference between CR group and HC group [3,40 (1,20-8,50)] was significant (p<0.05) however, the difference between CR group and PC group [6,00 (1,80-55,50)] was not significant (p>0.05). B10 cell levels were higher in the HC group [5,90 (2,90-8,50)] when compared to the other groups. The difference between HC group and PC group [4,10 (0,10-5,90)] was significant (p<0.05) however the difference between HC group and CR group [4,20 (0,10-7,40)] was not significant (p>0.05). BR1 cell levels were significantly higher in the HC group [5,50 (2,80-10,80)] when compared to both CR group [0,50 (0,20-4,60)] and PC group [0,80 (0,30-1,70)] (p<0.05). CR group had higher levels of BR1 cells than the PC group but the difference was not significant (p>0.05). Breg subtypes were higher in the CR group than in the PC group, except for BR1 cells, although the differences did not reach significant levels. There are many studies showing the inhibitory functions of Bregs, and there are studies indicating that Breg levels are high in transplant tissue-tolerant individuals (114,115). The results of our study, which do not agree with these studies, were evaluated as the temporal variability of B cell levels in the posttransplant period and the lack of clear knowledge of the mechanisms that induce Breg induction. At the present stage, the results for Bregs are not enough to use Breg levels as an adjunct parameter in the diagnosis of chronic rejection. Further studies are needed on the effect of Breg levels on transplant results.