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Atomic force microscopy: dancing on the stage of immunology

Cellular & Molecular Immunology volume 18, pages 1605–1606 (2021)Cite this article

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Biomechanical properties are critical in regulating gene expression, protein synthesis, and macromolecule conformation, thus profoundly influencing the migration, proliferation, and apoptosis of cells.1 Applying a force to the contact area of a cell results in stress, which is described as the force per unit contact area, and causes cell deformation. The deformation degree is positively related to the stress. To describe the ability of a cell to resist deformation, the term “stiffness” is commonly used as the ratio of stress to deformation. Cell stiffness is mainly decided by intracellular actin filaments (F-actin) but not by the plasma membrane because the plasma membrane only contributes 1/1000–1/10,000 of the stiffness to the cell.2 Different cell types possess different stiffnesses, which match the corresponding tissue stiffness and allow the cell to properly sense and respond to mechanical cues. Cell stiffness in the human body may range from 0.01 to 12 kPa.

At least two methods are currently available to measure cell stiffness. One is magnetic twisting cytometry (MTC), which twists RGD (Arg-Gly-Asp)-coated magnetic microbeads bound to membrane integrins and measures bead rotation with a magnetometer. The measured distortion range is calculated to reflect the cell stiffness or mechanical force. Another method is atomic force microscopy (AFM), which is different from MTC as well as traditional optical and electronic microscopes. AFM does not need a light or electron source; instead, it uses a sharp probe to contact the surface of an object, such as a biomaterial or a cell, to obtain clear information. A key AFM component is the probe, which is a cantilever with a tip. The tip is at the end of the cantilever and is used to touch the sample in a process that is similar to using a finger to touch the sample, but here, the ‘finger’ is tiny and soft. By applying a force to let the probe gradually approach and contact the sample surface, the stiffness of the sample causes the cantilever to bend. When leaving the surface of the sample upon retraction, the curvature of the cantilever will decrease but is still attracted downward due to the adhesion between the tip and sample. Such deflection of the cantilever can be transformed into an image by the detection laser, photodetection, and piezoelectric actuator. Thus, the height, stiffness, and adhesion of a sample can be deduced from the force curve.

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Authors and Affiliations

  1. Department of Immunology & National Key Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences (CAMS) & Peking Union Medical College, Beijing, China

    Bo Huang

  2. Department of Biochemistry & Molecular Biology, Tongji Medical College, Huazhong University of Science & Technology, Wuhan, China

    Bo Huang

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  1. Bo Huang
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Correspondence to Bo Huang.

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Huang, B. Atomic force microscopy: dancing on the stage of immunology. Cell Mol Immunol 18, 1605–1606 (2021). https://doi.org/10.1038/s41423-021-00664-1

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  • DOI: https://doi.org/10.1038/s41423-021-00664-1

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