This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
The following feature is common to both cytotoxic T - cells and NK cells - 
Select and explain. 
A. Synthesize antibody, B. Require antibodies to be present for action, C. Effective against virus infected cells, D. Recognize antigen in association with HLA class II markers
C: Effective against virus infected cells
Answer: C: Effective against virus infected cells 
Explanation: 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