ABSTRACT
OBJECTIVE This study aimed to investigate the influence of IgD on T/B cell activationand construct hIgD-Fc-Ig fusion protein to competitive inhibition IgD binding with IgDR. METHODS T/B cells were sorted by magnetic cell sorting. The differences of mIgD and IgD-R level between different T/B cell subtypes were detected by FCM. Serum IgD level was detected by ELISA. Human IgD-Fc-IgG1- Fc sequence was amplified by cross- PCR and then subcloned into PET28a(+ ) empty vector. After prokaryotic expression through escherichia coli, we obtained the hIgD-Fc-Ig fusion protein by affinity chromatograph. Western blot was used to identify the hIgD- Fc- Ig fusion protein. Human peripheral blood monouclear cells (PBMC) and fibroblast like synoviocytes (FLS) proliferation were detected using a cell counting kit-8 (CCK-8). RESULTS The percentage of CD3+/CD4+, CD3+/IgD+, CD3+/CD4+/IgD+, CD3+/IgD-R+ and CD3+/CD4+/IgD-R+ cells increased significantly in RA patients comparing to healthy people. IgD can stimulate PBMC proliferation. IgD (1, 3, 10, 30 μg·mL-1) stimulate PBMC proliferation significantly after 24 h. We obtained stable and active hIgD-Fc-Ig fusion protein. The hIgD-Fc-Ig 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 hIgD-Fc-Ig fusion protein may competitively inhibit IgD's function and may play an therapeutic role in autoimmune diseases.