Most important cells acting against virus and cancer cells are?

Ans. is 'b' i.e., Natural killer cells * Virus infected cells and tumor (cancer) cells are killed by NK cells and cytotoxic T-cells Natural killer cells (NK cells)* These cells possess cytotoxic activity against virus infected cells, tumor cells and transplanted foreign cells.* Cytotoxicity of NK cells is neither antibody dependent nor MHC restricted. Activity is nonimmune as it does not require antigenic stimulation.* NK-cells are positive for CD 16 and CD56.* NK cells are usually negative for CD3, but a subset is positive for CD3 called NK/T-cells.* IL-2 acts as a growth factor for NK cells. NK cells activity is augmented by interferon. NK cells secrete peroforin (resembles complement C9) which causes transmembrane pores through which cytotoxic factors (e.g. TNF-(3) enters the cells and induce apoptosis.