Identification of an activation-related protein in B cells in the ABO incompatible condition.

In ABO-incompatible (ABOi) kidney transplantation (KT), antibodies can mediate immunological accommodation or immune rejection, but the mechanism by which B cells are induced to produce antibodies with different functions is still unclear. Previous research established an ABOi kidney cell model and identified that haptoglobin (HP) is associated with the activation of lymphocytes. In the present study, the results of a flow cytometric assay demonstrated that HP was expressed by B cells. Moreover, dot-ELISA and ELISA analyses showed that the concentrations of total IgG, blood group B antibody, IgG1, IgG2 and IgG4 were all significantly increased in the cell model. In addition, dot-ELISA and haptoglobin level analyses showed that HP protein expression was significantly increased, while RT-qPCR assay indicated that HP was significantly reduced at the mRNA level. Furthermore, bioinformatics analysis showed that HP could interact with Smad3, and the HP-Smad3 complex was detected in a peripheral blood mononuclear cell (PBMC) protein extract by a dot-ELISA method. This research revealed that HP was involved in the process of B-cell activation by interacting with Smad3, and the results will be helpful to reveal the mechanism of B-cell activation in ABOi-KT.