Phagocytic ‘teeth’ and myosin-II ‘jaw’ power target constriction during phagocytosis

Abstract

Phagocytosis requires rapid actin reorganization and spatially controlled force generation to ingest targets ranging from pathogens to apoptotic cells. How actomyosin activity directs membrane extensions to engulf such diverse targets remains unclear. Here, we combine lattice light-sheet microscopy (LLSM) with microparticle traction force microscopy (MP-TFM) to quantify actin dynamics and subcellular forces during macrophage phagocytosis. We show that spatially localized forces leading to target constriction are prominent during phagocytosis of antibody-opsonized targets. This constriction is largely driven by Arp2/3-mediated assembly of discrete actin protrusions containing myosin 1e and 1f (‘teeth’) that appear to be interconnected in a ring-like organization. Contractile myosin-II activity contributes to late-stage phagocytic force generation and progression, supporting a specific role in phagocytic cup closure. Observations of partial target eating attempts and sudden target release via a popping mechanism suggest that constriction may be critical for resolving complex in vivo target encounters. Overall, our findings present a phagocytic cup shaping mechanism that is distinct from cytoskeletal remodeling in 2D cell motility and may contribute to mechanosensing and phagocytic plasticity.

Mechanisms of frustrated phagocytic spreading of human neutrophils on antibody-coated surfaces

“…For example, F-actin accumulation at the front of the phagocytic cup has been shown to be correlated with force production during macrophage phagocytosis (Nelsen et al, 2020). Novel techniques to measure phagocytic forces with high resolution hold great promise for illuminating the detailed mechanisms linking actin remodeling to force generation (Vorselen et al, 2021; Vorselen et al, 2020). It seems plausible to ascribe the local character of this cytoskeletal remodeling to localized signaling triggered by fresh cell-substrate contact.…”

Actin nano-architecture of phagocytic podosomes

“…On closed phagosomes, podosomes were found to be partially resistant to inhibition of the actin nucleator Arp2/3 17 , a key component of conventional podosomes. In contrast, the number of phagocytic teeth at the phagocytic cup were significantly reduced upon the inhibition of Arp2/3 16 . Much remains unknown about the nature and role of the podosome-like structures at the phagocytic cup.…”

“…Podosomes and podosome-like structures all appear to consist of a tightly packed actin core surrounded by a looser actin meshwork which includes radial actin fibers that extend away from the core 12 . The structures formed during phagocytosis have been called "podosome-like structures" [13][14][15] , phagocytic "teeth" 16 and phagosome-associated podosomes 17 . Phagocytic podosomes recruit proteins like those in other podosomes, but they are shorter-lived, with higher turnover at the phagocytic cup 15 .…”

T Cell Traction Forces show temporal patterns which Depend on Stimulation and Cell Subtype

“…The forces exerted by these cells are expected to be comparatively feeble and less localized. Nevertheless, the ability of immune cells to generate and respond to forces is at the heart of their function in a variety of situations, ranging from phagocytosis (Herant 2006; Vorselen et al 2020; 2021; Jaumouillé and Waterman 2020) and stop/go signal for migration (Jannat, Dembo, and Hammer 2011; S. H. J. Kim and Hammer 2021; Huse 2017), to antigen extraction and maturation by B cells (Spillane and Tolar 2018; Kumari et al 2019) and early activation of T cells (Hu and Butte 2016; Thauland et al 2017; Klotzsch and Schütz 2013; Y.…”