Hypersensitivity reactions and primary immunodeficiency disorders as tested on USMLE Step 1.
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- Which antibody class mediates Type I hypersensitivity reactions?
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IgE- In Type I hypersensitivity, IgE cross-linking on which two effector cell types triggers degranulation?
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Mast cells and basophils- The immediate-phase response of Type I hypersensitivity begins within ____ of allergen exposure.
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minutes- Which two antibody classes mediate Type II hypersensitivity reactions?
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IgG and IgM- In Type II hypersensitivity, antibodies bind antigens located where?
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On the cell surface or in the extracellular matrix- Goodpasture syndrome, caused by antibodies against glomerular and alveolar basement membranes, is a classic example of Type ____ hypersensitivity.
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II- In myasthenia gravis, autoantibodies against the acetylcholine receptor cause weakness through what mechanism?
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Blocking (functionally inhibiting) the receptor- In Graves disease, autoantibodies against the TSH receptor cause hyperthyroidism through what mechanism?
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Stimulating the receptor- What does a direct Coombs test detect?
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Antibody already bound to the patient's own red blood cells- What does an indirect Coombs test detect?
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Free antibody present in the patient's serum- What is the underlying tissue-damage mechanism in Type III hypersensitivity?
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Antigen-antibody immune complexes deposit in tissue and activate complement, attracting neutrophils- Serum sickness, in which immune complexes form against a foreign protein such as an antitoxin, exemplifies which hypersensitivity type?
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Type III- Type IV hypersensitivity is mediated by which cells, without involvement of antibody?
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T lymphocytes- A mutation in the BTK gene, which blocks B cell maturation, causes which primary immunodeficiency?
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X-linked agammaglobulinemia (Bruton)- The most common primary immunodeficiency disorder is ____.
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selective IgA deficiency
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