When we test how soft a mattress is, or squeeze a pear to find out whether it is ripe, we are assessing something’s mechanical properties. It has also been known for some years that these mechanical properties can distinguish cells from each other. Three years ago, Dr. Oliver Otto from the University of Greifswald and scientists from the TU Dresden developed a technique called real-time deformability cytometry (RT-DC) to measure the mechanical properties of cells. So far, however, this has only been able to measure how elastic the cells are. Now the team has further developed the method so that they can also work out a cell’s viscosity. The simultaneous measurement of these two things allows the scientists to find out exactly which cell types are located in a tiny drop of blood within a few seconds. With the new dynamic RT-DC (dRT-DC), it is even possible to distinguish between certain subtypes of immune cells, the B and T lymphocytes. "Previously, this was only possible by using fluorescence-labelled antibodies or complex computer programs," explains DZHK scientist Dr. Otto, who heads the biomechanics research group at the University of Greifswald.
Under existing technology, researchers must already know what they are looking for, using matched ‘labels’ and fluorescent dyes for the cell they want to find. Cells are labelled with a fluorescence-labelled antibody that recognizes a structure on their surface but this ‘fluorescence-labelling’ can alter the properties and function of the cells. This new, label-free, method offers researchers the great advantage that they can simply analyze a sample and interpret the data to find out what is there, without a starting point, and dRT-DC does not alter the cells themselves.
The new dRT-DC method can measure viscosity and elasticity of up to 100 cells per second, making it a potentially powerful research tool.
Photo-shoots in the channel
With RT-DC, the cells are pushed through a narrow channel, which squashes them and causes them to deform, as they are recorded by a camera. Bob Fregin, a PhD student in Dr. Otto's research group, has improved the method by increasing the number of images taken of each cell. "Previously we only had a snapshot of the deformed cell, but now we can observe in real time how its shape changes as it flows through the channel and can use it to calculate not only the elasticity but also how viscous the cell is," said Fregin explaining the principle of dRT-DC.
The scientists from Greifswald regard their method as complementary to previous tools. "Our approach also provides rapid information on which cell types are present and whether their number has changed in comparison to the other cells in the blood," explains Otto. "Based on these results in combination with the mechanical properties of the cells, further targeted investigations can then be carried out, for example on the molecular changes.”
From the mechanical properties, the scientists can also determine whether immune cells are activated or not. Activated immune cells are a sign that inflammation is present in the body. "The ability of the dRT-DC to identify and characterize cells in a cell mixture might be relevant for a better understanding of the role of the immune system in acute and chronic diseases," said Professor Stephan Felix, Director of the Clinic and Polyclinic for Internal Medicine at the University Hospital of Freiburg. In Greifswald, dRT-DC is used to investigate how inflammation-related cardiovascular diseases develop. The first promising results have already been obtained from ongoing projects.
Original work: High-throughput single-cell rheology in complex samples by dynamic real-time deformability cytometry. Fregin B, Czerwinski F, Biedenweg D, Girardo S, Gross S, Aurich K, Otto O. Nat. commun. 2019 Jan 24;10(1):415. DOI: 10,1038/s41467-019-08370-3.
Christine Vollgraf, Press and Public Relations, German Centre for Cardiovascular Research (DZHK), Tel.: 030 3465 529 02, presse(at)dzhk.de
Dr. Oliver Otto, Center for Innovation Competence HIKE Humoral Immune Reactions in Cardiovascular Diseases, University of Greifswald, oliver.otto(at)uni-greifswald.de