<prompt> The following feature is common to both cytotoxic T - cells and NK cells -Synthesize antibodyRequire antibodies to be present for actionEffective against virus infected cellsRecognize antigen in association with HLA class II markers  <response>: Ans. is c i.e., Effective against virus infected cells Natural killer cells o are first line of defense against virus laden cells and neoplastic cells o cytotoxity is not MHC restricted Cytotoxic T cells o they are antigen specific T cells whose function is to produce antigen specific lysis of target cells by direct cell-to-cell contact. o are usually CD, class I MHC restricted T cells. o are impoant in defense against viral infections of tissues. Thus the feature common to both cytotoxic T-cells and NK cells is effectivity against virus infected cells. Cytotoxicity of different cells o Natural killar cells o Cytotoxic T-cells o Antibody dependent cytotoxic T-cells ADCC a type of null cell Not antibody dependent Not MHC restricted Class I MHC restricted Not antibody dependent Antibody dependent Not MHC restricted 