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. HN (Hemagglutinin-neuraminidase) is a type II glycoprotein with 576 amino acids that is found in the outer coat of many paramyxoviruses, including human parainfluenza virus, mumps virus, and the avian pathogen Newcastle disease virus. It codes for a 63.8 kDa molecule in which there exist five potential asparagine-linked glycosylation sites. HN protein can make infection easier through assisting virus particles binding to cells. The C-terminal portion, the cytoplasmic tail of HN, forms a globular head that is a site responsible for its biological activities and is thought to manage its incorporation into viral particles. In addition, HN contains a neuraminidase activity which may allow the detachment of viral particles at the end of the cell cycle.