You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is First line of defence against tumor and virus? and explain in detail?
Ref: Robbins review E-Book, P 67* NK cells have the ability to respond without prior sensitization.* They carry receptors for MHC class I molecules which inhibit their lytic function. When expression of class I MHC molecules is reduced on a cell surface by viral interference, inhibitory receptors on NK cells do not receive a negative signal and the targeted cells is destroyed.* NK cells have CD16, Fc receptor that allows them to bind to opsonized cells and lyse them. This is a form of type II hypersensitivity with antibody mediated disease.