A 25-year-old patient with X-linked agammaglobulinemia (Bruton's disease) is evaluated for susceptibility to infections. Which of the following immunological findings would best distinguish this condition from common variable immunodeficiency (CVID)?
- A Absent peripheral B cells with normal T cell counts ✓
- B Absent serum immunoglobulins
- C Normal B cell numbers with defective antibody production
- D Absent T cells with normal B cells
Explanation
X-linked agammaglobulinemia (XLA) is caused by mutations in Bruton's tyrosine kinase (BTK), which is essential for pre-B cell maturation. The hallmark is absence of mature B cells in peripheral blood (CD19+/CD20+ cells virtually undetectable) with normal T cell counts and low/absent immunoglobulins. In CVID, B cells are present in normal numbers but fail to differentiate into plasma cells, resulting in poor antibody production despite normal B cell counts. This distinction is critical: flow cytometry showing absent peripheral B cells is diagnostic of XLA, while CVID shows B cells present but functionally impaired.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.