These are a group of enzymes secreted by natural killer (NK) cells.
cytokines
interferons
selectins
granzymes and perforins
The Correct Answer is D
A. Cytokines: Cytokines are signaling molecules secreted by various immune cells to coordinate immune responses. While NK cells do secrete cytokines to activate other immune cells, cytokines themselves are not the enzymes that directly kill target cells.
B. Interferons: Interferons are proteins released by virus-infected cells that help inhibit viral replication and activate immune responses. They do not directly destroy target cells and are not classified as enzymes secreted by NK cells.
C. Selectins: Selectins are adhesion molecules that mediate the rolling of leukocytes along blood vessel walls during inflammation. They are unrelated to NK cell cytotoxic activity and do not function as killing enzymes.
D. Granzymes and perforins: NK cells secrete granzymes and perforins to induce apoptosis in virus-infected or abnormal cells. Perforins form pores in the target cell membrane, allowing granzymes to enter and trigger programmed cell death, providing a rapid innate immune defense.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. A decrease in oxygen levels:While low oxygen levels stimulate chemoreceptors, baroreceptors are not primarily sensitive to oxygen. Their function is focused on detecting pressure changes rather than gas concentrations.
B. Changes in arterial pressure:Baroreceptors in the carotid sinus and aortic arch detect stretch in the arterial walls caused by increases or decreases in blood pressure. This information is sent to the cardiovascular center to regulate heart rate and vessel tone, making them pressure-sensitive sensors.
C. An increase in oxygen levels:High oxygen levels do not directly affect baroreceptor activity. Baroreceptors respond to mechanical stretch, not oxygen concentration, so oxygen changes are irrelevant to their primary function.
D. A decrease in carbon dioxide:Carbon dioxide levels primarily influence chemoreceptors, not baroreceptors. While CO₂ can indirectly affect cardiovascular responses, baroreceptors themselves do not respond to changes in CO₂.
Correct Answer is B
Explanation
A. T cells:T lymphocytes are part of the adaptive immune system and require specific antigen recognition for activation. They provide targeted responses and immunological memory but do not act immediately. Their function is delayed compared to innate immune cells, so they are not a component of innate defenses.
B. Natural killer cells:Natural killer (NK) cells are innate immune cells that act without prior sensitization. They can recognize and destroy virus-infected or abnormal cells immediately. This rapid, non-specific action provides a critical first line of defense against infections and tumor cells.
C. Plasma cells:Plasma cells are differentiated B cells that secrete antibodies as part of the adaptive immune response. They take several days to develop after antigen exposure and are not involved in immediate, non-specific innate defense mechanisms.
D. B cells:B lymphocytes belong to the adaptive immune system and require activation by antigens and helper T cells to produce antibodies. Their responses are specific and delayed, unlike innate immune cells that respond immediately to threats.
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