GED Science TestLife ScienceHard
A medical researcher is studying a group of individuals who exhibit a unique genetic trait: they are immune to a specific viral infection that commonly affects the general population. Further investigation reveals that these individuals have a mutation that prevents the virus from binding to the host cells. Which of the following components of the immune system is most directly responsible for recognizing and targeting virus-infected host cells, thereby preventing the spread of the infection within the body?
- AMacrophages
- BB lymphocytes
- CNatural killer cells
- DCytotoxic T lymphocytes
Show answer & explanationAnswer & explanation
Correct answer: D. Cytotoxic T lymphocytes
Cytotoxic T lymphocytes (CTLs), also known as killer T cells, are specialized immune cells that directly recognize and destroy host cells that have been infected by viruses or have become cancerous. They play a crucial role in cell-mediated immunity by identifying specific viral antigens presented on the surface of infected cells.
Why the other options are wrong
- A. Macrophages are phagocytic cells that engulf pathogens and cellular debris, and present antigens, but they are not the primary cells responsible for directly killing infected host cells in a specific manner.
- B. B lymphocytes produce antibodies, which primarily target extracellular pathogens and toxins, not infected host cells.
- C. Natural killer cells are part of the innate immune system and can kill abnormal cells (like infected or cancerous cells) without prior sensitization, but CTLs provide a more specific, adaptive response to virus-infected cells.
Cytotoxic T Lymphocytes (CTLs)
Specialized immune cells that directly recognize and kill host cells infected with intracellular pathogens (like viruses) or cancerous cells by identifying specific antigens presented on their surface.
- Part of adaptive immune system.
- Recognize specific antigens presented by MHC Class I molecules.
- Induce apoptosis (programmed cell death) in target cells.
Memory trick: T-cells Target Trouble, B-cells Block Badness.