CD74 & CD22

CD22 is a B-cell-specific transmembrane glycoprotein belonging to the SIGLEC (sialic acid-binding immunoglobulin-like lectin) family. It is encoded by the CD22 gene located on chromosome 19q13.1. CD22 plays a crucial role in B-cell signaling and immune response modulation. It acts primarily as an inhibitory co-receptor that regulates B-cell receptor (BCR) signaling, thereby preventing overactivation of B cells and reducing the risk of autoimmunity. CD22 binds to sialylated glycans and recruits SHP-1 (Src homology region 2 domain-containing phosphatase-1), a phosphatase that dampens signaling cascades.

CD74 is a transmembrane glycoprotein primarily expressed on antigen-presenting cells (APCs), including B cells, dendritic cells, macrophages, and monocytes. It is best known as the invariant chain (Ii) of the major histocompatibility complex (MHC) class II molecules. CD74 plays an essential role in the trafficking and processing of MHC class II molecules during their synthesis and transport to the cell surface, where they present antigens to CD4+ T cells.