Anionic antimicrobial peptide-lysozyme interactions in innate pulmonary immunity

Area of Science:

• Pulmonary immunology
• Antimicrobial mechanisms
• Innate immunity

Background:

• The respiratory tract relies on antimicrobial factors in airway surface liquid (ASL) for defense.
• Interactions between co-existing antimicrobial molecules in ASL are poorly understood.
• Cationic lysozyme and anionic antimicrobial peptides (AP) are present in high ASL concentrations.

Purpose of the Study:

• To evaluate potential antagonistic, additive, or synergistic interactions between lysozyme and AP.
• To determine how salt concentration affects the antimicrobial activity of lysozyme and AP.
• To assess the combined antimicrobial efficacy of lysozyme and AP relevant to physiological conditions.

Main Methods:

• Bacterial strains (Pasteurella haemolytica, Micrococcus lysodeikticus, Pseudomonas aeruginosa) were exposed to varying concentrations of lysozyme and H-GADDDDD-OH (AP) in 50, 100, or 150 mM NaCl.
• Minimum Inhibitory Concentrations (MICs) were determined after a 2-hour incubation period.
• Interactions were assessed by comparing MICs of individual components versus their combination.

Main Results:

• MICs of AP generally increased with higher NaCl concentrations against all tested bacteria.
• MICs of lysozyme increased with NaCl for P. haemolytica and M. lysodeikticus, but not P. aeruginosa.
• No significant interactions affecting antimicrobial activity were observed when lysozyme and AP were combined.

Conclusions:

• Increasing NaCl concentrations can slightly reduce the efficacy of both lysozyme and AP.
• Lysozyme and AP do not exhibit significant synergistic or antagonistic interactions at physiologically relevant concentrations.
• Pulmonary innate defense mechanisms involving lysozyme and AP may function independently under varying salt conditions.