First line of defence against tumour and virus?

NK cells Ability to kill virus-infected cells and tumor cells NK cells act as an early line of defense against viral infections and some tumors. Two cell surface molecules, CD16 and CD56, are commonly used to identify NK cells. CD16 is an Fc receptor for IgG, and it confers on NK cells the ability to lyse IgG-coated target cells. This phenomenon is known as antibody-dependent cell-mediated cytotoxicity (ADCC). The functional activity of NK cells is regulated by a balance between signals from activating and inhibitory receptors NK cell inhibitory receptors recognize self-class I MHC molecules, which are expressed on all healthy cells. The inhibitory receptors prevent NK cells from killing normal cells. Virus infection or neoplastic transformation often enhances expression of ligands for activating receptors and at the same time reduces the expression of class I MHC molecules.