Primary B-cell immunodeficiencies
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A 9-year-old with recurrent pneumococcal pneumonia has normal neutrophil counts and oxidative-burst testing. In a complement-free assay, healthy donor neutrophils ingest encapsulated bacteria poorly when the bacteria are incubated with the patient’s serum. Adding purified, pathogen-specific donor IgG restores ingestion. Selectively blocking Fc-gamma receptors on the donor neutrophils abolishes this rescue.