LadHyX, CNRS, École polytechnique, Institut Polytechnique de Paris, Palaiseau, France; Institut de Chimie Physique, CNRS UMR 8000, Université Paris-Saclay, Orsay, France.
Institut de Chimie Physique, CNRS UMR 8000, Université Paris-Saclay, Orsay, France.
Biophys J. 2022 Apr 19;121(8):1381-1394. doi: 10.1016/j.bpj.2022.03.021. Epub 2022 Mar 19.
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.
吞噬细胞构成了生物体的第一道防线，吞噬微生物病原体。吞噬作用涉及到尚未被很好理解的细胞力学变化。理解这些力学变化有望揭示触发病理并发症的免疫过程。以前的研究表明，吞噬细胞在其靶标周围经历一系列的伸展事件，随后细胞张力增加。似乎与之矛盾的是，其他研究观察到细胞张力的增加伴随着膜的扩张。尽管吞噬细胞是粘弹性的，但很少有研究量化吞噬过程中的粘性变化。也不清楚细胞系的力学行为是否与原代中性粒细胞相似。我们通过使用免疫球蛋白 G 包被的 8-和 20-μm 直径的珠作为靶标，研究了吞噬过程中同时或顺序伸展和力学变化的问题。我们使用基于微管的单细胞流变仪监测 PLB 细胞和原代人中性粒细胞吞噬过程中的粘弹性特性。我们表明，PLB 细胞在较大的珠上更快的扩展是一个几何效应，反映了吞噬杯的恒定推进速度。细胞在 20-μm 珠上比在 8-μm 珠上更硬，PLB 细胞伸展和变硬的相对时间取决于靶标大小：在较大的珠上，变硬在达到最大伸展面积之前开始，但在达到最大面积之后结束。在较小的珠上，细胞吞噬珠后刚度开始增加。与 PLB 细胞类似，原代细胞在较大的珠上变得更硬，但开始伸展和变硬更快，并且在两种珠大小上的伸展结束之前变硬开始。我们的结果表明，吞噬细胞中的力学变化不是细胞伸展的直接结果，并且吞噬作用的模型应该加以修正，以解释除了膜扩张之外导致细胞变硬的原因。
