A child has recurrent Staphylococcus epidermidis and Pseudomonas infections since birth. The umbilical cord separated at day 28. Abscesses contain scanty pus despite marked peripheral blood neutrophilia. Flow cytometry shows absence of CD11b on neutrophils. The defective molecule functions as:

• A A chemokine receptor required for neutrophil priming
• B An opsonin receptor for C3b-mediated phagocytosis
• C A selectin ligand mediating rolling along endothelium
• D The beta-2 integrin subunit needed for firm adhesion of neutrophils to endothelium ✓

Explanation

This is leukocyte adhesion deficiency type 1 from mutations in ITGB2 encoding the CD18 beta chain shared by LFA-1, Mac-1 and p150,95. Without beta-2 integrins, neutrophils roll normally but cannot achieve firm adhesion or transmigration, giving absent pus, delayed cord separation and neutrophilia. Selectin defects cause LAD type 2 with a different phenotype including mental retardation, and C3b receptor loss would impair phagocytosis rather than extravasation.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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