The percentages of CD4+CD69+, CD4+CD154+, CD19+CD23+, CD19+CD21+, CD19+IgD+, and CD19-CD138+ were increased and the percentages of CD4+CD62L+ were decreased in RA patients after treatment of IgD, which suggest that IgD promote the activation and maturation of T cells and B cells, and enhanced the activation of plasma cells. Here, SDC1 is linked to rheumatoid arthritis.