CD19 (Cluster of differentiation 19), also known as B-lymphocyte antigen CD19, is a 95 kDa transmembrane glycoprotein on the surface of the immunoglobulin superfamily (IgSF) and classified as a type I one-pass transmembrane protein. It maps to the short arm of chromosome 16p11.2 encoded by the 7.41 kilobite CD19 gene that produces a 556-amino acid protein with two extracellular C-type IgSF domains together with a 242-residue cytoplasmic tail that exhibits highly conservation between mouse and human. The CD19 molecules are expressed from the earliest stage of B cells development until plasma cells terminal differentiation. It can associate with the B cell antigen receptor (BCR), CD81 (TAPA-1), CD38, CD21, CD22 and CD225 to establish intrinsic B cell signaling and reduce the thresholds. CD22 (Cluster of differentiation 22), also referred to SIGLEC2 or B-cell receptor CD22, is a 135-140 kDa transmembrane glycoprotein and a member of the SIGLEC family of lectins. The protein encoded by this gene is localized at the chromosome 19q13.12 and codes for alternative spliced forms including CD22, CD22α, and CD22β. of which the latter is the predominant species expressed by B cells. The expression of CD22 is restricted to the cytoplasm of pre-B cells and progenitor in the early B-cell development. CD22 serves as a cell adhesion receptor for sialic acid-bearing ligands which is expressed on erythrocytes and all leukocytes. Additionally, CD22-mediated signal transduction can activate B cells and modulate antigen receptor signaling in vitro.