Explain why cytotoxic t cells are activated bya braoder range of host cells than

Cytotoxic T cells are the only T lymphocytes that directly attack and kill other cells. They are particularly responsive to cells of transplanted tissues and organs, cancer cells, and host cells that are infected with viruses, intracellular parasites, or bacteria.

When a TC cell recognizes a complex of antigen and MHC-I protein on a diseased or foreign cell, it “docks” on that cell, delivers a lethal hit of cytotoxic chemicals that will destroy it, and goes off in search of other enemy cells while the chemicals do their work. Among these chemicals are (1) perforin, which creates holes in its plasma membrane and destroys the cell in the same manner as the perforin released by natural killer cells; (2) lymphotoxin, which destroys the target cell’s DNA; and (3) tumor necrosis factor (TNF), which kills cancer cells by unknown mechanisms and stimulates fever, leukopoiesis, and eosinophil activity. TC cells also secrete interferon, which inhibits the replication of viruses, and interleukins that regulate macrophage activity, as the interleukins of the TH cells do.