A 2-month-old infant presents with delayed separation of the umbilical cord, omphalitis, and recurrent skin infections without pus formation. Flow cytometry shows absence of CD18 on leukocytes. Which step in leukocyte extravasation is defective in this patient?
- A Tight adhesion ✓
- B Rolling
- C Transmigration
- D Chemotaxis
Correct answer: A. Tight adhesion
Explanation
Leukocyte Adhesion Deficiency type 1 is caused by a deficiency of CD18, the beta-2 integrin subunit. Integrins mediate tight adhesion of leukocytes to endothelial cells via ICAM-1. Rolling is mediated by selectins, and transmigration occurs after adhesion. The lack of pus is due to the inability of neutrophils to adhere and migrate to the site.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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