title: Frustrated Phagocytic Spreading of J774A-1 Macrophages Ends in Myosin II-Dependent Contraction.
abstract: Conventional studies of dynamic phagocytic behavior have been limited in terms of spatial and temporal resolution due to the inherent three-dimensionality and small features of phagocytosis. To overcome these issues, we use a series of frustrated phagocytosis assays to quantitatively characterize phagocytic spreading dynamics. Our investigation reveals that frustrated phagocytic spreading occurs in phases and is punctuated by a distinct period of contraction. The spreading duration and peak contact areas are independent of the surface opsonin density, although the opsonin density does affect the likelihood that a cell will spread. This reinforces the idea that phagocytosis dynamics are primarily dictated by cytoskeletal activity. Structured illumination microscopy reveals that F-actin is reorganized during the course of frustrated phagocytosis. F-actin in early stages is consistent with that observed in lamellipodial protrusions. During the contraction phase, it is bundled into fibers that surround the cell and is reminiscent of a contractile belt. Using traction force microscopy, we show that cells exert significant strain on the underlying substrate during the contraction phase but little strain during the spreading phase, demonstrating that phagocytes actively constrict during late-stage phagocytosis. We also find that late-stage contraction initiates after the cell surface area increases by 225%, which is consistent with the point at which cortical tension begins to rise. Moreover, reducing tension by exposing cells to hypertonic buffer shifts the onset of contraction to occur in larger contact areas. Together, these findings provide further evidence that tension plays a significant role in signaling late-stage phagocytic activity.
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia; Department of Physics, Emory University, Atlanta, Georgia.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Kovari
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Wenbin
authors.initials: W
authors.lastname: Wei
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Patrick
authors.initials: P
authors.lastname: Chang
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Jan-Simon
authors.initials: JS
authors.lastname: Toro
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Ruth Fogg
authors.initials: RF
authors.lastname: Beach
authors.affiliation: Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Dwight
authors.initials: D
authors.lastname: Chambers
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Karen
authors.initials: K
authors.lastname: Porter
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia.
authors.forename: Doyeon
authors.initials: D
authors.lastname: Koo
authors.affiliation: School of Physics, Georgia Institute of Technology, Atlanta, Georgia. Electronic address: jennifer.curtis@physics.gatech.edu.
authors.forename: Jennifer E
authors.initials: JE
authors.lastname: Curtis
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D002021:Buffers; D002460:Cell Line; D048430:Cell Shape; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism; D055595:Mechanical Phenomena; D051379:Mice; D024462:Myosin Type II / Q000378:metabolism*; D010587:Phagocytosis
chemical_list: D000199:Actins; D002021:Buffers; D024462:Myosin Type II