MEDizzy - A 12-month-old boy with a 6-month history of repeated

Feed Library Learning Discuss Leaderboard Journal

Inflammation and Repair

A 12-month-old boy with a 6-month history of repeated infections has had a fever and cough for the past 3 days. A Gram stain of sputum shows many gram-positive cocci in chains. CBC shows neutrophilia. Laboratory studies show that the patient’s neutrophils phagocytose and kill organisms promptly in the presence of normal human serum, but not in his own serum. The neutrophils migrate normally in a chemotaxis assay. Which of the following is the most likely cause of this boy’s increased susceptibility to infection?

ExplanationThis immunoglobulin deficiency prevents opsonization and phagocytosis of microbes. A deficiency of integrins and selectins, or a defect in microtubules, would prevent the adhesion and locomotion of neutrophils. H2O2 production is part of the oxygen-dependent killing mechanism. This mechanism is intact in this patient because the neutrophils are able to kill bacteria when immunoglobulins in normal serum allow phagocytosis.