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Blood & Immune Immunology — Step 1 practice questions
31 questions in this area, with an explanation for every answer choice.
Three samples below, free and without an account.
How this shows up on Step 1
Immunology questions in this section combine two things the exam tests separately elsewhere. Examined as mechanism throughout: which cell, which signal, which step. Anaemia questions are approached through indices before anything else, and the classification tree does most of the work.
Sample questions
Sample question 1
An infant has delayed separation of the umbilical cord, recurrent infections without pus formation, and marked leukocytosis. Which of the following is the most likely diagnosis?
Explanations
A. DiGeorge syndrome
DiGeorge syndrome presents with hypocalcemia and cardiac defects, a different presentation.
B. Bruton agammaglobulinemia
Bruton agammaglobulinemia presents with recurrent bacterial infections from absent B cells, without this specific cord separation/pus pattern.
C. Leukocyte adhesion deficiency · correct
Delayed umbilical cord separation, recurrent infections WITHOUT pus formation (since neutrophils cannot properly migrate to sites of infection), and marked leukocytosis (since neutrophils accumulate in blood but cannot exit vessels) are classic for leukocyte adhesion deficiency, caused by defective integrin (CD18) function.
D. Chronic granulomatous disease
CGD presents with catalase-positive organism infections and granuloma formation, not this delayed cord separation/absent pus pattern.
E. Chediak-Higashi syndrome
Chediak-Higashi syndrome presents with partial albinism and giant granules in neutrophils, a different presentation.
Sample question 2
Which of the following vaccine types uses a live but weakened form of the pathogen, generally producing a strong, long-lasting immune response but is generally contraindicated in significantly immunocompromised patients?
Explanations
A. Live attenuated vaccine · correct
Live attenuated vaccines use a weakened form of the live pathogen, generally producing robust, long-lasting immunity (often closely mimicking natural infection), but carry a small risk of causing disease in significantly immunocompromised individuals, making them generally contraindicated in that population.
B. mRNA vaccine
mRNA vaccines deliver genetic instructions for an antigen, not a live pathogen, and are generally considered safe in immunocompromised patients as well.
C. Inactivated (killed) vaccine
Inactivated (killed) vaccines use a dead pathogen, generally safer for immunocompromised patients but often requiring booster doses for durable immunity.
D. Toxoid vaccine
Toxoid vaccines use inactivated toxins, not live organisms.
E. Subunit vaccine
Subunit vaccines use only specific pathogen components, also generally safe for immunocompromised patients.
Sample question 3
Which of the following mediators, released during the LATE phase of a type I hypersensitivity reaction, is primarily responsible for prolonged bronchoconstriction and inflammation, distinct from the immediate histamine-mediated response?
Explanations
A. Leukotrienes · correct
Leukotrienes (along with other mediators like prostaglandins and cytokines released from activated mast cells and recruited inflammatory cells) drive the late-phase response in type I hypersensitivity, causing more prolonged bronchoconstriction and tissue inflammation, which is why leukotriene receptor antagonists have a therapeutic role in asthma.
B. Complement C3b
Complement C3b is an opsonin from complement activation, not the primary late-phase mediator in type I hypersensitivity.
C. IgG
IgG is not the primary mediator of type I hypersensitivity (that is IgE); this option does not describe the late-phase mediator being asked about.
D. Histamine exclusively, with no late phase mediators
Histamine is primarily responsible for the IMMEDIATE phase; additional mediators drive the late phase response.
E. IgM
IgM is not the primary mediator of type I hypersensitivity.
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