CH6 - Effector mechanisms of t cell mediated immunity Flashcards
Q - What are the types of T lymphocyte–mediated immune reactions that eliminate microbes that are sequestered in the vesicles of phagocytes and microbes that live in the cytoplasm of infected host cells?
Intracellular microbes that reside in phagosomes, including several bacterial and fungal species, are eliminated by helper T cells, especially those of the Th1 subset that activate phagocytes to destroy ingested microbes. Microbes whose life cycle includes time spent in the cytosol, mainly viruses, may be eliminated
Q - What are the major subsets of CD4+ effector T cells, how do they differ, and what are their roles in defense against different types of infectious pathogens?
Th1 cells secrete the cytokine interferon-γ (IFN-γ, which activates macrophages to kill phagocytosed microbes. Th2 cells secrete IL-4 and IL-13, which stimulate intestinal mucus production and gut peristalsis, and IL-5, which activates eosinophils. IL-4 and IL-13 secreted by follicular helper T (Tfh) cells induce B cell IgE production, and IgE bound to eosinophils and mast cells contributes to immunity against helminths. Th2 cells are involved in defense against helminths. Th17 cells secrete IL-17, which recruits neutrophils, which ingest and destroy extracellular fungi and bacteria.
Q - What are the mechanisms by which T cells activate macrophages, and what are the responses of macrophages that result in the killing of ingested microbes?
Activated Th1 cells secrete cytokines such as interferon-γ that activate macrophages. These helper T cells also express CD40 ligand, which activate macrophages by engaging CD40. Activated macrophages then induce nitric oxide synthase to make nitric oxide and activate NADPH oxidase to generate reactive oxygen species. These free radicals can destroy ingested microbes. Activated macrophages also produce increased amounts of lysosomal enzymes, which help to destroy microbes, and other molecules that promote inflammation and call more leukocytes into the reaction.
Q - How do CD8+ CTLs kill cells infected with viruses?
CD8+ T cells that recognize antigen on an infected tissue cell release granules that contain perforin and granzymes, which enter the infected cells recognized by the T lymphocytes and induce apoptosis of these infected cells.
Q - What are some of the mechanisms by which intracellular microbes resist the effector mechanisms of cell-mediated immunity?
Some intracellular microbes evade immunity by preventing phagolysosomal fusion. Other intracellular microbes express molecules that can inactivate host complement responses. Many viruses inhibit antigen presentation and some may inactivate effector T cells.
