P20023

CD21 also known as CR2 is a type I integral membrane glycoprotein that plays a crucial role in the immune system by serving as a receptor for the C3d complement fragment and the Epstein-Barr virus. CD21 expression on mature B cells, follicular dendritic cells, and certain epithelial cells is vital for B cell activation and proliferation, as CD21 enhances the signaling strength of the B cell antigen receptor (BCR) in conjunction with the co-receptor CD19. This interaction is essential for the adaptive immune response, as CD21 modulates the activation threshold of B cells, ensuring a robust and specific response to foreign antigens. Additionally, CD21 undergoes phosphorylation following B cell activation, which is a key post-translational modification that influences downstream signaling pathways and cellular outcomes.