Servicenavigation

Project Details

Back

Projekt Print View

Cellular mechanics of particle binding and phagocytosis investigated by photonic force microscopy and high-speed imaging

Subject Area Biophysics
Term from 2011 to 2020
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 189771364
 
Final Report Year 2024

Final Report Abstract

The binding of particles such as bacteria, viruses or debris to living cells and the possible uptake into the cell interior – phagocytosis – represent central processes in cell biology and immunology. The observation of such binding and uptake processes, which usually occur stepwise, is limited by the spatial and temporal resolution of light microscopes. Despite modern fluorescence techniques, fluctuation-based processes, such as the (re-)organization of molecular bonds can hardly be observed or analyzed. Until recently, the measurement of binding strengths had not been possible at all and processes like binding, particle transport or active engulfment into the cell body are not sufficiently understood, especially not regarding the cell mechanics. The smaller the particle or the cellular structure, the faster are their movements. Many processes occur on scales of nanometers and milliseconds, which have not been addressable by most optical methods - especially for living cells. Using highly developed measurement techniques such as Photonic Force Microscopy (PFM) equipped with dynamic optical tweezers and MHz 3D interferometric particle tracking, such as 100 Hz super-resolving label-free microscopy (by Rotating Coherent Scattering) or fast 3D fluorescence microscopy (TIRF, SIM, Light-Sheet, confocal spinning disc), fascinating novel interaction concepts between particles and the periphery of cells could be unravelled. By spectral decomposition of thermal particle fluctuation recorded with PFM, we could analyse and reveal smallest or even hidden interactions of particles nearby the cell membrane, allowing to identify the varying interaction strengths of different cellular components. By investigating the role of membrane fluctuations during particle binding and uptake with PFM, we found that the uptake energy into a GUV becomes predictable since the energy increases for smaller fluctuation amplitudes and longer relaxation time. E.g. the reduced particle uptake energy for protein-ligand interactions LecA-Gb3 or Biotin-Streptavidin results also from pronounced, low-friction membrane fluctuations. Using 100 Hz ROCS microscopy, we were the first to monitor how numerous tiny, fluctuating, virus mimicking particles attached to the jagged periphery of macrophages and analysed their biding behaviour. Mean thermal fluctuation amplitudes decreased within 15 minutes from 20nm to 10 nm leading to a fivefold increase in binding stiffness. Another remarkable result was that we were able to show that filopodia (”fingers”) of macrophage (killer) cells pull at particles, e.g. presented in optical traps. After successive failing and pulling, the filopodium can increase its pulling force over time finally withdraw the particle for further uptake. We have been able to unravel and explain this process, being likely a frequent process in the immune response during infection. Several other biologically interesting and relevant findings are described in the report. This has become possible by further advances in optical technologies such as ROCS microscopy, Fourier plane interferometric tracking or electric-tunable-lens controlled spinning disc confocal microscopy, which we have all developed or improved within the scope of this project.

Publications

 
 

Additional Information

© 2026 DFG Disclaimer / Copyright / Privacy Policy

Textvergrößerung und Kontrastanpassung