Natural killer cells are especially effective against which targets?

Natural killer cells are especially effective against which targets?

• A. Bacteria in extracellular fluids
• B. Cancer and virus-infected cells
• C. Parasites
• D. Normal host cells

Answer: (B)

Natural killer cells are specialized for recognizing and destroying abnormal cells, especially those that are cancerous or infected by viruses. They act early and without prior sensitization, sensing stressed or “missing self” cells that have reduced MHC I or show activating signals. When they encounter such targets, NK cells release perforin and granzymes to induce apoptosis, and they can also engage death-receptor pathways. They may also participate in antibody-dependent cellular cytotoxicity when antibodies coat infected or tumor cells. In contrast, free bacteria in extracellular fluids are more effectively handled by antibodies, complement, and phagocytes; parasites are typically dealt with by eosinophils and IgE-mediated responses; normal, healthy host cells are not the usual targets unless they become stressed or transformed. That’s why the best target for NK cells is cancer cells and virus-infected cells.

Natural killer cells are specialized for recognizing and destroying abnormal cells, especially those that are cancerous or infected by viruses. They act early and without prior sensitization, sensing stressed or “missing self” cells that have reduced MHC I or show activating signals. When they encounter such targets, NK cells release perforin and granzymes to induce apoptosis, and they can also engage death-receptor pathways. They may also participate in antibody-dependent cellular cytotoxicity when antibodies coat infected or tumor cells.

In contrast, free bacteria in extracellular fluids are more effectively handled by antibodies, complement, and phagocytes; parasites are typically dealt with by eosinophils and IgE-mediated responses; normal, healthy host cells are not the usual targets unless they become stressed or transformed. That’s why the best target for NK cells is cancer cells and virus-infected cells.