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: Microbiology
Components of innate immunity that are active against viral cells include: March 2009 
Select and explain. 
A. Cytotoxic T cells, B. B cell, C. NK cells, D. All of the above
C: NK cells
Answer: C: NK cells 
Explanation: Ans. C: NK cells Natural killer cells/NK cells are a type of cytotoxic lymphocyte that constitute a major component of the innate immune system. NK cells play a major role in the rejection of tumors and cells infected by viruses. They kill cells by releasing small cytoplasmic granules of proteins called perforin and granzyme that cause the target cell to die by apoptosis.