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Aim:Investigate the influence of IgD on T/B cell activation and construct hIgDFcIg fusion protein to competitive inhibition IgD binding with IgDR.Methods T/B cells were sorted by magnetic cell sorting.The differences of mIgD and IgDR level between different T/B cell subtypes were detected by FCM.Serum IgD level was detected by ELISA.Human IgDFcIgG1Fc sequence was amplified by crossPCR and then subcloned into PET28a(+) empty vector.After prokaryotic expression through escherichia? coli, we obtained the hlgDFeIg fusion protein by affinity chromatograph.Western blot was used to identify the hIgDFcIg fusion protein.Human peripheral blood monouclear cells (PBMC) and fibroblast like synoviocytes (FLS) proliferation were detected using a cell counting kit8 (CCK8).Results The percentage of CD3 +/CI4 + , CD3 +/IgD + , CD3 +/CD4 +/IgD + ,CD3 +/IgDR + and CD3 +/CD4 +/IgDR + cells increased significantly in RA patients comparing to healthy people.IgD can stimulate PBMC proliferation.IgD (1, 3, 10, 30 μg · ml1) stimulate PBMC proliferation significantly after 24 h.We obtained stable and active hIgDFcIg fusion protein.The hlgDFcIg fusion protein showed no effect on PBMC proliferation.But it could downregulate human IgD protein promoting proliferation effects in human PBMC.Conclusion This result suggests that IgD and IgDR play an important role on T/B cell activation in RA patients and the hIgDFcIg fusion protein may competitively inhibit IgD s function and may play an therapeutic role in autoimmune diseases.