X-linked agammaglobulinemia is due to a defect in which protein?

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Study for the NBME Immunology Test. Study with flashcards and multiple choice questions, each question includes hints and explanations. Prepare to excel!

Multiple Choice

X-linked agammaglobulinemia is due to a defect in which protein?

Explanation:
Bruton’s tyrosine kinase is essential for signaling through the B cell receptor and for B cell maturation. When BTK is defective, B cells cannot progress from the pro-B/pre-B stage to mature B cells, so there are very few circulating B cells and immunoglobulins of all isotypes are markedly reduced. This humoral immunodeficiency presents with recurrent bacterial infections in affected males, reflecting the X-linked inheritance of BTK. In contrast, issues with CD40L impair class switching (Hyper-IgM due to CD40-CD40L interaction), AID affects class switching and somatic hypermutation, and RAG1 defects disrupt V(D)J recombination, leading to more severe combined immunodeficiencies. Therefore, the defect described fits Bruton's tyrosine kinase.

Bruton’s tyrosine kinase is essential for signaling through the B cell receptor and for B cell maturation. When BTK is defective, B cells cannot progress from the pro-B/pre-B stage to mature B cells, so there are very few circulating B cells and immunoglobulins of all isotypes are markedly reduced. This humoral immunodeficiency presents with recurrent bacterial infections in affected males, reflecting the X-linked inheritance of BTK. In contrast, issues with CD40L impair class switching (Hyper-IgM due to CD40-CD40L interaction), AID affects class switching and somatic hypermutation, and RAG1 defects disrupt V(D)J recombination, leading to more severe combined immunodeficiencies. Therefore, the defect described fits Bruton's tyrosine kinase.

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