Department of Pure and Applied Physics, Graduate School of Advanced Science and Engineering, Waseda University, Tokyo, Japan.
Department of Physics, School of Advanced Science and Engineering, Waseda University, Tokyo, Japan.
Biophys J. 2023 Jul 11;122(13):2707-2726. doi: 10.1016/j.bpj.2023.05.025. Epub 2023 May 24.
The zipper model has been dominantly used to describe the driving mechanism of the engulfment process and its specific identification of antigens during phagocytosis in macrophages. However, the abilities and limitations of the zipper model, capturing the process as an irreversible reaction, have not been examined yet under the critical conditions of engulfment capacity. Here, we demonstrated the phagocytic behavior of macrophages after reaching the maximum engulfment capacity by tracking the progression of their membrane extension during engulfment using IgG-coated nondigestible polystyrene beads and glass microneedles. The results showed that, after macrophages reached their maximum engulfment capacity, they induced membrane backtracking (the reverse phenomenon of engulfment) in both polystyrene beads and glass microneedles, regardless of the difference in the shape of these antigens. We evaluated the correlation of engulfment in simultaneous stimulations of two IgG-coated microneedles and found that each microneedle was regurgitated by the macrophage independently of the advancement or backtracking of membranes on the other microneedle. Moreover, assessing the total engulfment capacity determined by the maximum amount the macrophage was capable of engulfing when imposing each antigen geometry showed that the capacity increased as the attached antigen areas increased. These results indicate that the mechanism of engulfment should imply the following: 1) macrophages have a backtracking function to recover their phagocytic activity after reaching maximal engulfment limit, 2) both phagocytosis and backtracking are local phenomena of the macrophage membrane that operates independently, and 3) the maximum engulfment capacity is determined not only by mere local cell membrane capacity but also by the whole-cell volume increase during simultaneous phagocytosis of multiple antigens by the single macrophages. Thus, the phagocytic activity may entail a hidden backtracking function, adding to the conventionally known irreversible zipper-like ligand-receptor binding mechanism during membrane progression to recover the macrophages that are saturated from engulfing targets beyond their capacity.
拉链模型一直被用来描述吞噬过程的驱动机制及其在巨噬细胞吞噬过程中对特定抗原的识别。然而，在吞噬容量的临界条件下，尚未对拉链模型的能力和局限性进行检验，该模型将这一过程捕捉为不可逆反应。在这里，我们通过跟踪 IgG 包被的不可消化聚苯乙烯珠和玻璃微针在吞噬过程中细胞膜延伸的进展，展示了巨噬细胞在达到最大吞噬容量后的吞噬行为。结果表明，在巨噬细胞达到最大吞噬容量后，它们会在聚苯乙烯珠和玻璃微针中诱导膜回溯（吞噬的反向现象），而与这些抗原的形状差异无关。我们评估了同时刺激两个 IgG 包被微针时的吞噬相关性，发现每个微针都被巨噬细胞独立地吐出，而与另一个微针上的膜前进或回溯无关。此外，评估由巨噬细胞在施加每种抗原几何形状时能够吞噬的最大量确定的总吞噬容量表明，随着附着抗原面积的增加，容量增加。这些结果表明，吞噬的机制应该暗示以下几点：1）巨噬细胞具有回溯功能，可在达到最大吞噬极限后恢复其吞噬活性；2）吞噬和回溯都是巨噬细胞膜的局部现象，独立运作；3）最大吞噬容量不仅取决于单纯的局部细胞膜容量，还取决于单个巨噬细胞同时吞噬多个抗原时整个细胞体积的增加。因此，吞噬活性可能需要一种隐藏的回溯功能，补充了在膜进展过程中传统上已知的不可逆拉链样配体-受体结合机制，以恢复因吞噬能力超过目标而饱和的巨噬细胞。
