A newborn presents with severe lymphopenia (WBC 2,800/μL, lymphocytes 8%) discovered on routine screening after an older sibling died from Pneumocystis jirovecii pneumonia at 6 months. Vital signs are normal; temperature is 37.2°C. Flow cytometry demonstrates absent mature B and T lymphocytes with preserved natural killer cells. Chest X-ray shows no infiltrates. The infant has received no immunizations. Which of the following molecular processes is most likely defective in this infant?
- A)Expression of CD40 ligand on activated T cells
- B)Class switching from IgM to other immunoglobulin isotypes
- C)Oxidative burst generation in phagocytes
- D)Phosphorylation of tyrosine residues by BTK
- E)Recombination of variable, diversity, and joining gene segmentsGABARITO
Explicação
Absent mature B and T cells with preserved NK cells is characteristic of a defect in VDJ recombination, often due to RAG mutations. Without rearrangement of antigen receptor genes, lymphocyte precursors cannot generate functional B cell or T cell receptors. Ver explicação completa e trilha adaptativa →