In susceptible individuals, immune responses to otherwise innocuous antigens can produce allergic reactions upon reexposure to the same antigen. Most allergic reactions involve the production of IgE antibody against common environmental allergens. Some people are intrinsically prone to making IgE antibodies against many allergens, and such people are said to be atopic. IgE production is driven by antigen-specific TH2 cells; the response is skewed toward TH2 by an array of chemokines and cytokines that engage specific signaling pathways, including signals that activate ILC2 cells in submucosal tissues at sites of antigen entry. The IgE produced binds to the high-affinity IgE receptor FcεRI on mast cells and basophils. Specific effector T cells, mast cells, and eosinophils, in combination with TH1 and TH2 cytokines and chemokines, orchestrate chronic allergic inflammation, which is the major cause of the chronic morbidity of asthma. Failure to regulate these responses can occur at many levels of the immune system, including defects in regulatory T cells. Increasingly successful processes for suppressing allergic responses and reestablishing the ability to tolerate the sensitizing antigen are being developed, raising the hope of reducing the prevalence of allergic disorders. Antibodies of certain isotypes and various antigen-specific effector T cells contribute to allergic hypersensitivity to other antigens.
Questions.
14.1 True or False: Only TH2 cells can initiate the chain of signals needed to induce B cells to class-switch to IgE.
14.2 Multiple Choice: Which of the following has not been associated with genetic susceptibility to both allergic asthma and atopic eczema?
A. β subunit of FcεRI
B. GM-CSF C. IL-3 D. IL-4
E. IFN-γ 14.3 Different factors affect our susceptibility to allergic diseases. Which of the following is a false statement?
A. Environmental factors rarely contribute to the development of allergic disease.
B. The prevalence of atopy has been steadily increasing in the developed world.
C. Individuals with variant alleles of GSTP1 and GSTM1 have higher susceptibility to increased airway hyperactivity.
D. Children less than 6 months old who are exposed to other children in day care appear to be partially protected against asthma.
14.4 True or False: Like other antibodies, IgE is mainly found in body fluids.
14.5 Matching: Match the following options with the best 14.6 Which of the following statements is true?
A. Connective tissue mast cells do not participate in the initiation of an anaphylactic reaction.
B. Epinephrine should be avoided in patients suffering from anaphylactic shock as it may worsen the patient’s condition.
C. During anaphylactic shock, blood vessels lose permeability, and high blood pressure leads to death.
D. Penicillin can modify self proteins, causing an immune response with IgE production in some individuals that can lead to anaphylaxis upon re-encountering the drug.
14.7 Multiple Choice: Hypersensitivity reactions can cause pathology through the deposition of immune complexes. Which of the following is a mechanism by which immune complexes can be pathogenic? (More than one may apply.) ___ A. Immune complexes deposit in blood vessel walls.
___ B. IgE is cross-linked on the surface of mast cells and basophils, leading to activation. ___ C. Fc receptor ligation leads to leukocyte activation and tissue injury.
___ D. The complement system is activated, leading to the production of anaphylatoxin C5a. ___ E. CD8+ T cells are stimulated to secrete IL-4.