CD22 is a B cell-specific transmembrane glycoprotein belonging to the immunoglobulin superfamily, primarily serving as a regulator of the B cell receptor (BCR). It contains multiple immunoglobulin-like domains and regulates interactions and signaling between B cells and other cells by binding to sialic acid-containing glycans. CD22 is mainly expressed on the surface of mature B cells and participates in regulating antigen recognition, activation, proliferation, and survival by inhibiting overactive BCR signaling. The signaling pathways of CD22 involve PI3K and MAPK, playing a crucial role in B cell immune responses and self-tolerance. Specific expression and functional mutations of the CD22 gene are associated with certain autoimmune diseases and B cell tumors. Therefore, CD22 serves as an important molecular marker for studying B cell regulation mechanisms and developing therapeutic strategies for related diseases.