Certain viruses have evolved to be able to avoid detection by cytotoxic T cells. These viruses remove the MHC class 1 molecules from the surface of the cell that they are infecting. This ensures that the cytotoxic T cells do not bind to the infected cell and kill the cell and the virus within. Which immune cell is specifically designed to recognize these types of viral threats?

• A. CD4 effector cells.
• B. T helper cells.
• C. Regulatory T cells.
• D. Natural killer cells.
• E. CD8 effector cells.

Answer: (D)

Verified step by step guidance

1. Understand the role of MHC class 1 molecules: MHC class 1 molecules present endogenous antigens (such as viral proteins) on the surface of infected cells, allowing cytotoxic T cells (CD8+ T cells) to recognize and destroy these cells.
2. Recognize the problem: Certain viruses can evade detection by removing MHC class 1 molecules from the cell surface, preventing CD8+ T cells from recognizing and killing the infected cells.
3. Identify the immune cell type: Natural killer (NK) cells are a type of lymphocyte that can recognize and kill cells lacking MHC class 1 molecules. They are part of the innate immune system and can target cells that have downregulated MHC class 1, a common viral evasion strategy.
4. Differentiate between immune cells: CD4 effector cells, T helper cells, and regulatory T cells are primarily involved in coordinating the immune response and do not directly kill infected cells. CD8 effector cells require MHC class 1 for activation, unlike NK cells.
5. Conclude the solution: Natural killer cells are specifically designed to recognize and eliminate cells that have lost MHC class 1 expression, making them effective against viruses that use this evasion strategy.