The Change Of The PLCγ Pathway In Chronic Graft-versus-host Disease

Background and objective: Chronic graft versus host disease (cGVHD) is asevere complication after allogeneic hematopoietic stem celltransplantation(allo-HSCT). Recently, many studies have found that B cell play animportant role in the occurrence and development of cGVHD. Patients withcGVHD have disordered homeostasis of B cell and impaired B cell proliferation.BCR and BAFFR signal pathway are essential in B cell maturation and studiesfound that PLCγ2as a crosstalk downstream factor of BCR and BAFFR signalpathway play an important role in maintain of B cell homeostasis and establishmentof immune tolerance. Therefore, we speculated that there exist abnormal activationof BCR and BAFFR signaling pathway, especially PLCγ pathway in cGVHDpatients. Thus, we investigated the expression of specific B cell surface proteinsand PLCγ2in cGVHD patients’ peripheral B cells to study the change of PLCγsignaling pathway in cGVHD patients and explore the potential role of PLCγpathway in the pathogenesis of cGVHD.Methods：Blood were collected from33patients with cGVHD(17cases) andwithout cGVHD(16cases) after100days post allo-HSCT or from17healthyvolunteers in PLA general hospital in China.(1)Do statistical analysis of clinicalcharateristics of33patients involved in this study.(2)The expression of specific Bcell surface proteins, including IgM、BAFFR and CD20were detected by Flowcytometry.(3)The expression of phosphorylated PLCγ2in peripheral B cells weredetected by Flow cytometry to explore the change of PLCγ pathway in cGVHDpatients.(4)The PLCγ2and phosphorylated PLCγ2expression were detected byWestern Blot in the protein extracted from blood B cells acquired by using FlowSorting.Results：(1)Statistical analysis showed that there were no significant differences in age, sex, conditioning regimen, type of transplantation, occurrence ofaGVHD, or underlying hematologic malignancy between33patients with andwithout cGVHD in our study.(2) No difference were found in IgM、BAFFR andCD20expression of B cells in patients with cGVHD、without cGVHD and healthycontrols(p>0.05).(3)Flow cytometry showed that phosphorylated PLCγ2expression of B cells were significantly lower in patients with cGVHD than thosein patients without cGVHD and healthy participants(P<0.01), and after BCR werestimulated by IgM, the expression of phosphorylated PLCγ2wereincreased;Western blot showed that not only phosphorylated PLCγ2but PLCγ2decreased in cGVHD patients, which indicated that the low level of phosphorylatedPLCγ2in cGVHD patients were induced by decreased PLCγ2.Conclusions: There were no change of surface proteins in BCR and BAFFRpathway in cGVHD. The expression of phosphorylated PLCγ2and PLCγ2weredecreased in cGVHD patients. The ability of activation of PLCγ2were notimpaired in cGVHD, low level of phosphorylated PLCγ2were induced bydecreased PLCγ2. cGVHD patients experienced dysregulation of PLCγpathway,which were not related to the change of surface proteins in BCR andBAFFR signaling pathway, low expression of PLC γ2might be induced bysome unkown inhibitors. Deficiency of PLC γ2in B cells might take an activerole in the occurrence and development of cGVHD，furthermore, become abiomarker for detection of cGVHD and provide novel strategies to overcomecGVHD.