Microbiology Practice Exam

Which lymphocyte plays a key role in the defense against viral infections?

1. Natural killer cells

2. B-cells

3. Monocytes

4. Eosinophils

The correct answer is: Natural killer cells

Natural killer (NK) cells are a type of lymphocyte that is integral to the body's immune response against viral infections. These cells are part of the innate immune system, meaning they provide a rapid response to viral infections without the need for prior sensitization or the production of specific antibodies. NK cells recognize and kill virus-infected cells directly. They do this through several mechanisms, including the release of cytotoxic granules that contain perforin and granzymes. Perforin creates pores in the infected cell's membrane, while granzymes enter through these pores and induce apoptosis, or programmed cell death, in the target cell. In addition to directly killing infected cells, NK cells also produce cytokines, such as interferon-gamma (IFN-γ), which helps to enhance the overall immune response and activate other immune cells, including macrophages and T cells. This cooperative interaction bolsters the body's ability to control and eliminate viral infections. The other cell types mentioned, such as B-cells, are primarily responsible for the adaptive immune response by producing antibodies, while monocytes are more involved in phagocytosis and presenting antigens. Eosinophils primarily respond to parasitic infections and play a role in allergic reactions. Thus