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