CD3 (Cluster of differentiation 3), originally known as T3, is one of the first groups of human T lymphocyte surface antigens recognized by monoclonal antibodies. It has been reported that antibodies against CD3 could either stimulate T cells to divide or inhibit the progress of effector functions according to the conditions used. It plays an important role in T cell and the CD3 T-cell co-receptor helps to activate the cytotoxic T-Cell and T helper cells. The CD3 molecule is composed of a protein complex and consists of four distinct chains. The complex of mammals contains a CD3γ chain, a CD3δ chain, and two CD3ε chains. All these chains associate with T-cell receptor and the ζ-chain to generate an activation signal in T lymphocytes. 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.