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. FcαRI (Fc fragment of IgA receptor), also referred to FcalphaRI or CD89, is the most prominent and only human immunoglobulin A (IgA) Fc receptor that binds the heavy-chain constant region of IgA via two extracellular binding sites. This receptor is a transmembrane glycoprotein mapping at the chromosome 19q13.42 and belongs to the immunoglobulin (Ig) gene superfamily. FcαRI is expressed on the surface of blood myeloid cells, such as monocyte/macrophages, neutrophils, eosinophils, dendritic cells, and Kupffer cells, in which it mediates immunologic responses to pathogens. IgA plays an important role in immune protection. It interacts with IgA-opsonized targets and initiates a number of immunologic defense processes, for instance, phagocytosis, stimulation of the release of inflammatory mediators, and antibody-dependent cell-mediated cytotoxicity.