MEDizzy - A 20-year-old man steps into an elevator full of people with

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Immune System Diseases

A 20-year-old man steps into an elevator full of people with influenza who are coughing and sneezing. The influenza viral particles that he inhales attach to respiratory epithelium, and viral infection reduces MHC class I molecules displayed on these epithelial cells. Which of the following immune cells is most likely to rapidly destroy the virally infected cells?

ExplanationNatural killer (NK) cells have the ability to respond without prior sensitization. They carry receptors for MHC class I molecules, which inhibit their lytic function. When expression of class I MHC molecules is reduced on a cell surface by viral interference, the inhibitory receptors on NK cells do not receive a negative signal, and the targeted cell is killed. NK cells are often the first line of defense against viral infection. CD4-positive cells are helper T cells that assist other cells, such as NK cells, macrophages, and B cells, in the immune response. Dendritic cells aid in antigen presentation. Macrophages can phagocytize necrotic cells, then process and display any foreign antigens within those cells.