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Distinct timing of neutrophil spreading and stiffening during phagocytosis
Alexandra Zak1, Sophie Dupré-Crochet2, Elodie Hudik2
1LadHyX, CNRS, École polytechnique, Institut Polytechnique de Paris, Palaiseau, France; Institut de Chimie Physique, CNRS UMR 8000, Université Paris-Saclay, Orsay, France.
Abstract:
Phagocytic cells form the first line of defense in an organism, engulfing microbial pathogens. Phagocytosis involves cell mechanical changes that are not yet well understood. Understanding these mechanical modifications promises to shed light on the immune processes that trigger pathological complications. Previous studies showed that phagocytes undergo a sequence of spreading events around their target followed by an increase in cell tension. Seemingly in contradiction, other studies observed an increase in cell tension concomitant with membrane expansion. Even though phagocytes are viscoelastic, few studies have quantified viscous changes during phagocytosis. It is also unclear whether cell lines behave mechanically similarly to primary neutrophils. We addressed the question of simultaneous versus sequential spreading and mechanical changes during phagocytosis by using immunoglobulin-G-coated 8- and 20-μm-diameter beads as targets. We used a micropipette-based single-cell rheometer to monitor viscoelastic properties during phagocytosis by both neutrophil-like PLB cells and primary human neutrophils. We show that the faster expansion of PLB cells on larger beads is a geometrical effect reflecting a constant advancing speed of the phagocytic cup. Cells become stiffer on 20- than on 8-μm beads, and the relative timing of spreading and stiffening of PLB cells depends on target size: on larger beads, stiffening starts before maximal spreading area is reached but ends after reaching maximal area. On smaller beads, the stiffness begins to increase after cells have engulfed the bead. Similar to PLB cells, primary cells become stiffer on larger beads but start spreading and stiffen faster, and the stiffening begins before the end of spreading on both bead sizes. Our results show that mechanical changes in phagocytes are not a direct consequence of cell spreading and that models of phagocytosis should be amended to account for causes of cell stiffening other than membrane expansion.
Insights
Phagocytosis involves complex cell mechanics. This study reveals that cell stiffening during phagocytosis is not directly caused by cell spreading, but depends on target size and bead size. Models need revision.
Area of Science:
- Cellular mechanics
- Immunology
- Biophysics
Background:
- Phagocytosis is crucial for host defense, involving significant cell mechanical changes.
- The relationship between cell spreading, stiffening, and target size during phagocytosis remains unclear.
- Limited data exists on whether cell lines mimic primary neutrophil mechanics during phagocytosis.
Purpose of the Study:
- To investigate the interplay between cell spreading and mechanical changes during phagocytosis.
- To compare the phagocytic mechanics of neutrophil-like cell lines and primary human neutrophils.
- To determine the influence of target size on phagocytic cell mechanics.
Main Methods:
- Utilized immunoglobulin-G-coated microbeads (8- and 20-μm) as targets for phagocytosis.
- Employed a micropipette-based single-cell rheometer to measure viscoelastic properties.
- Monitored mechanical changes in both PLB cells and primary human neutrophils.
Main Results:
- Cell stiffening during phagocytosis is not solely a consequence of cell spreading.
- The timing of cell stiffening relative to spreading depends on the size of the phagocytic target.
- Primary human neutrophils exhibit faster spreading and stiffening kinetics than PLB cells, with stiffening preceding spreading completion.
Conclusions:
- Cell mechanical changes during phagocytosis are complex and influenced by factors beyond simple membrane expansion.
- The findings necessitate amendments to existing models of phagocytosis to incorporate additional mechanisms of cell stiffening.
- Understanding these mechanics is vital for elucidating immune responses and potential pathological complications.
