a. The influenza virus activates cell-mediated immunity because this type of immunity is responsible for recognizing and destroying virus-infected cells. When a person becomes infected with the influenza virus, the virus enters the host cells and replicates, which leads to the production of viral proteins on the surface of infected cells. These viral proteins can be recognized by cytotoxic T cells, which then kill the infected cells to prevent virus spread.
b. Cell-mediated immunity involves the activation of various types of T cells, including helper T cells, cytotoxic T cells, and memory T cells. When a virus infects a host cell, viral proteins are produced and presented on the surface of infected cells in the form of antigens. Helper T cells recognize the antigens and activate cytotoxic T cells, which are specialized in identifying and killing virus-infected cells. Cytotoxic T cells release cytokines and perforin to destroy the infected cells. Memory T cells are also activated during this process, and they can recognize and respond more quickly to future infections with the same virus. This allows the immune system to mount a more effective response upon subsequent exposures to the virus, which can lead to faster clearance of the virus and faster recovery.