Membrane damage and repair in primary monocytes exposed to human β-defensin-3

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Interactions between antimicrobial peptides (AMPs) and human immune cell plasma membranes are not well understood.
• Understanding these interactions is crucial for evaluating AMPs as potential human therapeutics.

Purpose of the Study:

• To investigate the differential susceptibility of human immune cells (monocytes, T cells, B cells) to the antimicrobial peptide human beta-defensin 3 (hBD-3).
• To elucidate the membrane-related mechanisms underlying monocyte sensitivity to hBD-3.

Main Methods:

• Analysis of propidium iodide (PI) exclusion to assess membrane integrity.
• Microscopic observation of bleb formation and LAMP1 expression as a membrane repair marker.
• Assessment of cellular cholesterol content via filipin staining.
• Investigation of phosphatidylserine (PS) exposure and its role in hBD-3 susceptibility.

Main Results:

• hBD-3 caused membrane perturbations and bleb formation in monocytes, but not T or B cells, at relevant concentrations.
• Monocytes exhibited increased LAMP1 expression and enhanced cell death upon hBD-3 exposure, particularly when membrane repair was inhibited.
• Outer membrane phosphatidylserine (PS) exposure in monocytes was identified as a key factor contributing to their increased susceptibility to hBD-3-induced membrane damage.

Conclusions:

• Monocytes are more susceptible to hBD-3-induced membrane damage than T or B cells, partly due to higher surface expression of negatively charged PS.
• The findings highlight the importance of evaluating AMP-induced membrane disruption across diverse human immune cell types for therapeutic development.
• Targeting or understanding PS exposure could be critical for the safe and effective use of AMPs in human therapies.