A 6-year-old child has a history of recurrent infections with pyogenic bacteria, including Staphylococcus aureus and Streptococcus pneumoniae. The infections are accompanied by a neutrophilic leukocytosis. Microscopic examination of a biopsy specimen obtained from an area of soft tissue necrosis shows microbial organisms, but very few neutrophils. An analysis of neutrophil function shows a defect in rolling. This child's increased susceptibility to infection is most likely caused by a defect in which of the following molecules?

A. Selectins
B. Integrins
C. Leukotriene B4
D. Complement C3b
E. NADPH oxidase

Explanation:

Selectins are a family of single pass transmembrane proteins (cell adhesion molecule) that involves in transient cell to cell attachment in blood stream

Selectin binds to specific sugar residue present on surface of target membrane thus selectin binding is carbohydrate and calcium dependent

Selectins mainly binds with integrin proteins (dimeric transmembrane proteins that consists of two subunits, both stabilized by non covalent interactions)

Selectins are considered as cell surface lectins that have evolved to mediate the adhesion of white blood cells to endothelial cells and platelets under flow

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