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NBME 24 Answers

nbme24/Block 4/Question#15

A 15-month-old boy is brought to the physician by ...

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submitted by neonem(278),

Lack of CD18 (LFA-1 integrin) on phagocytes is the cause of leukocyte adhesion deficiency type 1 (LAD1). Since phagocytes like neutrophils and macrophages can't get out of the bloodstream, they are stuck in the blood, hence the leukocytosis with WBC count > 10,000. Since the leukocytes are stuck in the blood, they can't mount an effective immune response against bacteria.

sunshinesweetheart  also for completeness, LFA-1 is an integrin that binds ICAM, so LAD1 results from a defect in tight binding +