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First published online 12 April 2005
doi: 10.1242/jcs.02275

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Mechanics of neutrophil phagocytosis: behavior of the cortical tension

Biomedical Engineering Department, Boston University, 44 Cummington Street, Boston, MA 02215, USA

View larger version (44K): [in a new window]   Fig. 1. (A) Layout of the experimental chamber with micropipette access from each side. (B) Measurement of the surface tension by a law of Laplace method. (C) Two geometries of phagocytosis.

View larger version (18K): [in a new window]   Fig. 2. Curves showing macroscopic cell area dilation over time during micropipette aspiration (numbers indicate aspiration pressure in cm H2O). (Left) Steady state area expansion under a fixed aspiration pressure. (Right) Initial jump followed by steady expansion (detail of left curve). Neutrophil radius was 4.1 µm and micropipette radius was 1.2 µm.

View larger version (17K): [in a new window]   Fig. 3. Cortical tension versus area expansion in neutrophils post partial aspiration (x) and in neutrophils post-phagocytosis (). Each data point represents a different neutrophil. The right panel shows in detail the boxed area in the left panel. Straight lines are fits to the aspiration data at less than 25% expansion (right) and more than 30% expansion (left; see Eqns 8 and 9).

View larger version (38K): [in a new window]   Fig. 4. (Top left) Histogram of percentage area of slack membrane taken up before viscous surface tension occurs under passive aspiration (24 cells, mean 5.7%, s.d. 1.5%). (Top right) As for top left but in phagocytosis (20 cells, mean 27%, s.d. 11%). (Bottom left) Histogram of the magnitude of the surface viscosity under passive aspiration (28 cells, mean 72 mN m–1 s, s.d. 41 mN m–1 s). (Bottom right) As for bottom left but in phagocytosis (15 cells, mean 200 mN m–1 s, s.d. 100 mN m–1 s).

View larger version (121K): [in a new window]   Fig. 5. (A) Phagocytosis of a bead of radius 1.1 µm by a neutrophil of radius 4.2 µm. (B) phagocytosis of a bead of radius 2.3 µm by a neutrophil of radius 4.2 µm. (C) left, phagocytosis of a bead of radius 3.3 µm by a neutrophil of radius 4.5 µm; right, attempted phagocytosis of a bead of radius 5.5 µm by a neutrophil of radius 4.4 µm. (D) Sequential phagocytosis of two beads of radii 1.6 and 1.7 µm by a neutrophil of radius 4.3 µm.

View larger version (29K): [in a new window]   Fig. 6. Percentage of bead circumference phagocytosed () and neutrophil cortical tension () versus time for cases shown in Fig. 5.

View larger version (24K): [in a new window]   Fig. 7. Phagocytosis of a 1.6 µm radius bead by a 4.2 µm radius neutrophil with a surface area pre-stretched by 14% by aspiration. Percentage of bead circumference phagocytosed () and neutrophil cortical tension () versus time.

View larger version (19K): [in a new window]   Fig. 8. (A) Sketch of the contributions from unwrinkling of membrane and from vesicular exocytosis to the increasing macroscopic cell surface area during phagocytosis. (B) Sketch of the hierarchical unraveling of membrane wrinkles with stronger cross-links as surface tension increases.