Ammonium decreases human polymorphonuclear leukocyte cytoskeletal actin

Area of Science:

• Immunology
• Cell Biology
• Microbiology

Background:

• Ammonium, a bacterial metabolic byproduct, is known to inhibit polymorphonuclear leukocyte (PMN) functions.
• Previous assumptions linked this inhibition to cytoplasmic alkalinization.

Purpose of the Study:

• To investigate the mechanism by which ammonium affects PMN function, specifically exploring the role of cytoskeletal actin alterations.
• To determine if ammonium's effects on chemotaxis, degranulation, and receptor recycling are independent of cytoplasmic alkalinization.

Main Methods:

• Assessed the impact of ammonium on fMLP-induced elastase release in PMNs.
• Quantified changes in cytoskeletal actin levels in resting and stimulated PMNs treated with ammonium.
• Examined the effect of ammonium on actin depolymerization rates and cytochalasin B/D-modulated actin dynamics.
• Investigated the role of pertussis toxin-sensitive pathways in ammonium's effects on cytoskeletal actin.

Main Results:

• Ammonium significantly inhibited fMLP-induced elastase release (85%).
• Ammonium decreased cytoskeletal actin in resting PMNs (38%) and accelerated fMLP-induced depolymerization (150%).
• Ammonium's effects on actin were observed even with cytochalasin B/D treatment and were independent of pertussis toxin-sensitive pathways.

Conclusions:

• Ammonium inhibits neutrophil function by altering cytoskeletal actin dynamics, leading to decreased degranulation and impaired motility.
• These findings offer new insights into the pathogenic mechanisms employed by bacterial pathogens.
• The mechanism of inhibition is independent of cytoplasmic alkalinization, highlighting a distinct pathway of immune cell dysfunction.