Gene function — Which listed gene encodes a protein central to white blood cell (neutrophil) microbicidal activity?

Introduction:
Gene symbols often encode clues about protein function. This question asks you to recognize which gene product is directly involved in a key white blood cell function, namely microbial killing by neutrophils.

Given Data / Assumptions:

• MPO stands for myeloperoxidase.
• Neutrophils use oxidative mechanisms within phagolysosomes.
• Other listed genes have unrelated functions.

Concept / Approach:
Myeloperoxidase uses hydrogen peroxide and chloride ions to produce hypochlorous acid, a potent antimicrobial species. Deficiency in MPO impairs microbicidal activity. In contrast, GLUT4 is a glucose transporter; DCP1 is linked to mRNA decapping; RP13 suggests ribosomal protein; LDLR is the low density lipoprotein receptor in lipid metabolism.

Step-by-Step Solution:

Verification / Alternative check:
Clinical assays measure MPO activity in neutrophils; hereditary MPO deficiency presents with impaired killing of certain fungi and bacteria.

Why Other Options Are Wrong:

• DCP1: mRNA processing (decapping), not leukocyte killing.
• GLUT4: insulin responsive glucose transporter in muscle/adipose.
• RP13: ribosomal protein family, housekeeping role.
• LDLR: lipoprotein uptake; cardiovascular relevance.

Common Pitfalls:
Choosing broadly immune-sounding names without verifying specific leukocyte functions; MPO is well established in neutrophil granules.

Final Answer:
MPO.