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. CD28 (Cluster of Differentiation 28) is a homodimeric stimulatory cell surface receptor of the immunoglobulin (Ig) superfamily that is located on the chromosome 2q33.2. It is expressed on naive T cells and has also been found on the surface of plasma cells, eosinophils, and neutrophils. CD28 remains the most extensively studied costimulatory molecular and is a primary one for T-cell activatio. The control of T-cell responses through CD28 co-stimulation provides a means of anti-self and antimicrobial immunity. CD28 is essential for the lymphocyte activation and survival. A number of antigen-experienced T-cells lose CD28, and then can be re-activated without its engagement. Diseases linked to CD28 involve mycosis fungoides and Sezary's disease and the related pathways are Th2 differentiation pathway and RET signaling.