〔Abstract〕 Objective To investigate immunoglobulin D(IgD) can activate the function of T cells through immunoglobulin D receptor(IgDR)-lymphocyte-specific protein tyrosine kinase(Lck) signaling on human T cells and its effect on B cell activation.Methods Peripheral blood from healthy controls and RA patients were collected and peripheral blood mononuclear cells(PBMCs) were separated. CD4+T cells and CD19+B cells were sorted by flow cell sorting. Different concentration of IgD-stimul-ated CD4+T cells were co-cultured with CD19+B cells in transwell chamber. Laser confocal microscopy was used to observe Lck and IgDR co-localization on CD4+T cells.Western blot was used to detect the protein expression of P-Lck and CD40 L on CD4+T cells and the protein expression of CD40 on CD19+B cells. CCK-8 method was used to detect the effect of IgD-stimulated T cells on B cell activation. Results IgD significantly up-regulated the co-expression of Lck and IgDR proteins and the expression of P-Lck protein on CD4+T cells of healthy control. Both in healthy controls and RA patients,IgD-stimulated T cells could induce B cell activation. IgD could significantly up-regulate the expression of CD40 L protein on CD4+T cells and the expression of CD40 protein on CD19+B cells. Conclusion IgD could activate T cells via the IgDR-Lck signaling and stimulate B cell activation by up-regulating protein expression of T-B co-stimulatory molecules CD40 L and CD40.