Moussaoui, S. | bioRxiv Science

bioRxiv2026

3' Plasma Membrane Phosphoinositides Sustain ROS Production at Persistent Non-canonical Phagocytic Cups that Promote Macrophage Control of Aspergillus fumigatus Hyphae

Aspergillus fumigatus is the leading cause of aspergillosis in immunocompromised individuals. Because A. fumigatus hyphae rapidly outgrow macrophages, they are generally thought to evade macrophage-mediated control once they exceed the size limits of phagocytosis, enabling invasive growth within host tissues. Here, we show that macrophages circumvent this limitation by capturing hyphal tips within persistent tubular phagocytic cups. Rather than resolving into complete phagosomes or disengaging from their targets, these long-lived open compartments maintain key features of phagocytic cups while progressively acquiring characteristics of maturing phagosomes. Their persistence sustains localized NOX2-dependent reactive oxygen species production, leading to hyphal-tip damage and restriction of fungal growth. Sustained PI(3,4)P2 signaling downstream of class I PI3K promotes prolonged NOX2 activity and is required for efficient hyphal restriction. Together, our findings reveal a previously unrecognized antifungal mechanism in which persistent phagocytic cups transform incomplete phagocytosis into sustained antimicrobial activity, extending macrophage control beyond the physical limits of engulfment.

cell biology↗

bioRxiv2024

Depletion of endomembrane reservoirs drives phagocytic appetite exhaustion in macrophages

During phagocytosis, a phagocytic cup grows via F-actin remodelling and localized secretion to entrap a particle within a phagosome, which then fuses with endosomes and lysosomes to digest the particle, followed by phagosome resolution. As spatially limited systems, phagocytes have a maximal phagocytic capacity, at which point further uptake must be blunted. However, the processes responsible for phagocytic appetite exhaustion as phagocytes reach their maximal phagocytic capacity are poorly defined. We found that macrophages at their capacity have lower surface levels of Fc{gamma} receptors but overexpression of these receptors did not increase their capacity, suggesting that receptor levels are not limiting. Instead, surface membrane in-folding, membrane tension, and cortical F-actin were all reduced in exhausted macrophages. While this might contribute to appetite suppression, we also found that "free" endosomes and lysosomes were severely depleted in exhausted macrophages. Consequently, focal exocytosis at sites of externally bound particles was blunted. In comparison, macrophages recovered their appetite if phagosome resolution was permitted. We propose that depletion of the endomembrane pools is a major determinant of phagocytic fatigue as macrophages reach their phagocytic capacity. Summary statementMacrophages that reach their maximal phagocytic capacity lose their appetite for further uptake. This appetite exhaustion is driven partly by depletion of endosomes and lysosomes, preventing growth of additional phagocytic cups.

cell biology↗