NBME Immunology

Question 1

Which mediator and cell type are central to type I (immediate) hypersensitivity?

Accepted Answer

IgE bound to mast cells

Answer

Type I hypersensitivity occurs when allergen cross-links IgE on mast cells and basophils, causing release of histamine and other mediators.

Question 2

A patient has recurrent Neisseria infections. Which immune deficiency is most likely?

Accepted Answer

Terminal complement (C5-C9) deficiency

Answer

Deficiency of the membrane attack complex components (C5-C9) impairs lysis of Neisseria species, which causes recurrent meningococcal and gonococcal infections.

Question 3

A 6-month-old boy has recurrent bacterial infections, absent CD19+ B cells and very low immunoglobulins of all classes. Which gene is mutated?

Accepted Answer

BTK

Answer

Bruton agammaglobulinemia is X-linked and caused by a mutation in Bruton tyrosine kinase, which blocks B-cell maturation. Infections begin after maternal IgG wanes at about 6 months.

Question 4

A newborn has hypocalcemic seizures, a conotruncal cardiac defect and absent thymic shadow. Which immune defect is expected?

Accepted Answer

T-cell deficiency

Answer

DiGeorge syndrome (22q11 deletion) involves failure of third and fourth pharyngeal pouch development. This causes thymic aplasia with T-cell deficiency and hypoparathyroidism.

Question 5

Which cells recognize antigen presented on MHC class II molecules?

Accepted Answer

CD4+ helper T cells

Answer

MHC class II is expressed on antigen-presenting cells and is recognized by CD4+ helper T cells. MHC class I presents to CD8+ T cells.

NBME Practice Test

NBME Practice Test

NBME Immunology