Ch. 16 Book Questions Immunity to Microbes Flashcards
Different types of immune responses may be required to protect against different types of pathogenic microbes. For example, antibody responses and complement activation are effective in combatting extracellular bacterial infections but not intracellular bacterial infections. Which of the following species is an intracellular bacterium and is therefore not susceptible to antibody-mediated immune mechanisms?
a. Staphylococcus aureus
b. Streptococcus pneumonia
c. Escherichia coli
d. Clostridium tetani
e. Legionella pneumophila
e. Legionella pneumophila
Legionella pneumophila, the causative agent of legionnaire’s disease, is a gram-negative intracellular bacterium. This bacterium produces a cytotoxin that causes cell lysis and acute lung injury and inflammation. Cell-mediated immunity is required for eradication of infection by this organism. The other bacteria listed are extracellular organisms.
Which of the following is NOT part of the innate immune response to extracellular bacteria?
a. Complement activation by peptidoglycan
b. Complement activation by mannose
c. Activation of phagocytes by Toll-like receptors
d. Bacterial killing by natural killer (NK) cells
e. Acute inflammation
d. Bacterial killing by natural killer (NK) cells
Although natural killer cells are part of the innate immune system, they kill infected cells, not extracellular organisms. Innate immune responses to extracellular bacteria include both the alternative complement pathway (activated by peptidoglycan and lipopolysaccharide) and the lectin pathway (activated by mannose-binding lectin). Activation of phagocytes by Toll-like receptors and acute inflammation are key components of the innate immune response to extracellular bacteria.
All of the following are known mechanisms by which extracellular bacteria evade the immune system EXCEPT:
a. Capsules that prevent phagocytosis
b. Inhibition of class I MHC expression
c. Genetic variation of surface antigens
d. Inhibition of complement activation
e. Scavenging of reactive oxygen intermediates
b. Inhibition of class I MHC expression
Class I MHC restricted T cells generally are not involved in immune responses to extracellular bacteria, because these microbes rarely survive within phagocytes and do not provide antigens to the class I MHC pathway of antigen presentation. Therefore, inhibition of class I MHC expression would not be an effective evasion mechanism, although it is effective for viruses. Encapsulated bacteria, such as pneumococci, cannot be readily phagocytosed without opsonization. Antigenic variation is used by Neisseria species, Escherichia coli, and Salmonella typhimurium to avoid recognition by antibodies. Many bacteria produce inhibitors of complement activation. Catalase-producing staphylococci scavenge reactive oxygen species produced by activated phagocytes.
A particular species of microbe evades the immune system by several mechanisms, including inhibiting phagosome fusion with lysosomes, degrading reactive nitrogen intermediates generated by nitric oxide synthetase, and inhibition of class II MHC expression. Which of the following is most likely to be this species of microorganism?
a. Streptococcus progenies
b. Candida albicans
c. Clostridium tetani
d. Poliovirus
e. Mycobacterium tuberculosis
e. Mycobacterium tuberculosis
The mechanisms listed in the question would provide protection for an intracellular organism that lives within phagosomes of macrophages, such as Mycobacterium tuberculosis. Fusion of phagosomes with lysosomes exposes internalized microbes to a toxic environment of low pH, proteolytic enzymes, and reactive oxygen intermediates. Streptococcus pyogenes and Clostridium tetani are extracellular bacteria that do survive inside phagocytes. Candida albicans is a fungus that also lives and grows outside of cells. Poliovirus replicates in the nucleus and cytoplasm of cells but does not reside within phagosomes.
All of the following are associated with immune responses to intracellular bacteria EXCEPT:
a. Interferon-γ production by bacterial-antigen-specific CD4+ T cells
b. Opsonization of infected cells by complement
c. Interleukin-12 production by macrophages
d. Granuloma formation
e. Cytotoxic T lymphocyte killing of infected macrophages
b. Opsonization of infected cells by complement
Complement opsonizes extracellular microbes, not infected cells. Fragments of the complement C3 protein that remain covalently attached to microbial surfaces, including C3b and iC3b, mediate phagocytosis of the microbes by complement receptor expressing phagocytes. Intracellular bacteria often stimulate a TH1 response in which CD4+ T cells secrete interferon (IFN)-γ. Interleukin-12 secretion by dendritic cells and infected macrophages promotes TH1 differentiation and IFN-γ production. If the microbes successfully resist killing within phagosomes, chronic antigen stimulation leads to granuloma formation. Often, intracellular bacterial antigens will leave the phagosome and enter the cytoplasm, where they will enter the class I MHC antigen presentation pathway and stimulate a CD8+ cytotoxic T lymphocyte response.
Which type of T cell is most important for defense against extracellular bacteria and fungi?
a. TH1
b. TH2
c. TH17
d. Cytotoxic T lymphocyte
e. NKT cell
c. TH17
Activated TH17 cells simulate acute inflammatory responses with neutrophil rich infiltrates. These responses protect against extracellular microbes. Patients with defects in TH17 differentiation suffer from mucocutaneous candidiasis and recurrent Staphylococcus aureus infections.
Which of the following microbes induces two forms of disease, depending on the genetics of the host, one form characterized by weak cell mediated immunity and widespread proliferation of the microbe in macrophages, and the second form characterized by strong cell mediated immunity and destructive granulomatous inflammation?
a. Candida albicans
b. Vibrio cholera
c. Corynebacterium diphtheria
d. Epstein Barr virus
e. Mycobacterium leprae
e. Mycobacterium leprae
Mycobacterium leprae cause leprosy. In lepromatous leprosy, patients mount weak cell-mediated responses to M. leprae antigens, and the bacteria proliferate within macrophages and cause destructive lesions in the skin and underlying tissue. In tuberculoid leprosy there is strong T cell-mediated immunity with granulomas that damage sensory nerves. Patients with the tuberculoid form of leprosy produce IFN-γ and IL-2 in lesions (indicative of TH1 cell activation), while patients with lepromatous leprosy produce less IFN-γ and sometimes more IL-4 and IL-10 (suggestive of TH2 cells).
One of the major ways innate immunity protects against viral infections is by the production of type I interferons (interferons α and β). Which of the following statements about type I interferons is NOT correct?
a. Type 1 interferons are induced by viral RNA binding to endosomal Toll like receptors
b. Type 1 interferons are induced by viral RNA binding in the cytosol binding to RIG like receptors
c. Type 1 interferon gene expression is induced by interferon response factors (IRFs)
d. The major source of type I interferons during viral infections are infected epithelial cells
e. Type I interferons act on cells to resist inhibit viral replication and to induce class I MHC
d. The major source of type I interferons during viral infections are infected epithelial cells
The major source of type I interferons during viral infections are plasmacytoid dendritic cells
