Walbaum Stefan, Ambrosy Benjamin, Schütz Paula, Bachg Anne C, Horsthemke Markus, Leusen Jeanette H W, Mócsai Attila, Hanley Peter J
Institut für Molekulare Zellbiologie, Westfälische Wilhems-Universität Münster, Münster, Germany.
Center for Translational Immunology, University Medical Center Utrecht, Utrecht, The Netherlands.
J Biol Chem. 2021 Jan-Jun;296:100256. doi: 10.1016/j.jbc.2021.100256. Epub 2021 Jan 8.
A long-standing hypothesis is that complement receptors (CRs), especially CR3, mediate sinking phagocytosis, but evidence is lacking. Alternatively, CRs have been reported to induce membrane ruffles or phagocytic cups, akin to those induced by Fcγ receptors (FcγRs), but the details of these events are unclear. Here we used real-time 3D imaging and KO mouse models to clarify how particles (human red blood cells) are internalized by resident peritoneal F4/80 cells (macrophages) via CRs and/or FcγRs. We first show that FcγRs mediate highly efficient, rapid (2-3 min) phagocytic cup formation, which is completely abolished by deletion or mutation of the FcR γ chain or conditional deletion of the signal transducer Syk. FcγR-mediated phagocytic cups robustly arise from any point of cell-particle contact, including filopodia. In the absence of CR3, FcγR-mediated phagocytic cups exhibit delayed closure and become aberrantly elongated. Independent of FcγRs, CR3 mediates sporadic ingestion of complement-opsonized particles by rapid phagocytic cup-like structures, typically emanating from membrane ruffles and largely prevented by deletion of the immunoreceptor tyrosine-based activation motif (ITAM) adaptors FcR γ chain and DAP12 or Syk. Deletion of ITAM adaptors or Syk clearly revealed that there is a slow (10-25 min) sinking mode of phagocytosis via a restricted orifice. In summary, we show that (1) CR3 indeed mediates a slow sinking mode of phagocytosis, which is accentuated by deletion of ITAM adaptors or Syk, (2) CR3 induces phagocytic cup-like structures, driven by ITAM adaptors and Syk, and (3) CR3 is involved in forming and closing FcγR-mediated phagocytic cups.
一个长期存在的假说是补体受体（CRs），尤其是CR3，介导下沉吞噬作用，但缺乏证据。另外，据报道CRs可诱导膜皱褶或吞噬杯，类似于由Fcγ受体（FcγRs）诱导的膜皱褶或吞噬杯，但这些事件的细节尚不清楚。在这里，我们使用实时3D成像和基因敲除小鼠模型来阐明颗粒（人类红细胞）是如何通过CRs和/或FcγRs被驻留腹膜F4/80细胞（巨噬细胞）内化的。我们首先表明，FcγRs介导高效、快速（2 - 3分钟）的吞噬杯形成，FcRγ链的缺失或突变或信号转导子Syk的条件性缺失可完全消除这种形成。FcγR介导的吞噬杯强烈地从细胞与颗粒接触的任何点产生，包括丝状伪足。在没有CR3的情况下，FcγR介导的吞噬杯表现出延迟闭合并异常伸长。独立于FcγRs，CR3通过快速的吞噬杯样结构介导补体调理颗粒的散在摄取，这些结构通常从膜皱褶发出，并且在免疫受体酪氨酸基激活基序（ITAM）衔接子FcRγ链和DAP12或Syk缺失时大部分被阻止。ITAM衔接子或Syk的缺失清楚地表明存在一种通过受限孔口的缓慢（10 - 25分钟）下沉吞噬模式。总之，我们表明：（1）CR3确实介导一种缓慢的下沉吞噬模式，ITAM衔接子或Syk的缺失会加剧这种模式；（2）CR3诱导由ITAM衔接子和Syk驱动的吞噬杯样结构；（3）CR3参与FcγR介导的吞噬杯的形成和闭合。
