Description: CD21 antigen is an integral membrane glycoprotein of molecular weight 140 kDa (encoded by CR2 gene /complement receptor 2/, also known as complement C3d- and Epstein-Barr virus receptor). Anti-CD21 is useful in the identification of follicular dendriditic cell matrix found in normal lymph nodes and tonsillar tissue. This antibody also labels follicular dendritic cell tumor/sarcomas. The antigen is absent on T-lymphocytes, monocytes, and granulocytes.