Increased frequencies of memory and activated B cells and follicular helper T cells are positively associated with high levels of activation-induced cytidine deaminase in patients with immunoglobulin A nephropathy

The aim of the present study was to examine the frequencies of different subsets of B and follicular helper T (Tfh) lymphocytes in patients with immunoglobulin A nephropathy (IgAN), and investigate the potential underlying mechanism. A total of 27 patients with IgAN and 10 healthy controls (HC) were recruited for analysis of the frequencies of different subsets of B and Tfh cells. ELISA was used to analyze the concentration of serum interleukin (IL)-21. The transcriptional levels of activation-induced cytidine deaminase (AID) in the B cells were determined using reverse transcription-quantitative polymerase chain reaction, while the translational levels of AID were analyzed using western blotting. The frequencies of circulating memory and activated B cells and Tfh cells were found to be significantly increased in the IgAN groups, compared with those of the HC group, although the number of plasma cells were not significantly different between the two IgAN groups. In addition, the serum levels of IL-21 were found to be higher in the patients with IgAN, and correlated with 24-h proteinuria. IL-21 also enhanced the expression levels of AID in the B cells. The data of the present study revealed that the high levels of memory and activated B cells and Tfh cells were positively associated with the progression of IgAN, and that this may be mediated by the overexpression of AID, which is potentially regulated by IL-21.