New tool for visualizing leukocytes in the brain

Fluorescent antibody tool enables visualization of leukocytes in the brain vasculature during in vivo two-photon laser scanning microscopy.
25 May 2022
Representative two-photon images of cell labeling in cerebral microvasculature
Representative two-photon images of cell labeling in cerebral microvasculature: (left) superficial cortical microvessels, (right, top) cells flowing through capillaries, (right, bottom) leukocytes deforming to fit in capillaries. Image credit: Faulhaber et al., doi 10.1117/1.NPh.9.3.031917.

Tracking the movement of immune cells in health and disease can help us understand the mechanisms that recruit inflammatory white blood cells, also known as leukocytes, to tissue targets. Cell-mediated inflammation is an important cause of neurologic disorders such as multiple sclerosis. To treat such disorders successfully, we must understand and modulate the behavior of inflammatory cells. To date, most investigators have used genetically encoded markers for imaging leukocytes in live animal models. However, this is not always feasible.

As reported in Neurophotonics, researchers at the Center for Developmental Biology and Regenerative Medicine at Seattle Children’s Research Institute have shown that a well-validated antibody targeting the leukocyte marker, CD45, is a useful tool to add to the live imaging armamentarium.

CD45 is a cell-surface protein that is ubiquitously expressed by all types of white blood cells. When the antibody is injected intravenously, it binds to CD45 and labels the cell. The antibody can be tagged with a variety of fluorescent molecules to make it detectable via microscopy. The researchers show that this strategy can be successfully employed to visualize circulating leukocytes in brain microvessels via two-photon laser scanning microscopy.

A translucent window is placed into the skull of a mouse, allowing a direct view of the blood vessels of the cerebral cortex. When fluorescently labeled CD45 antibodies are injected during imaging, they decorate all the circulating white blood cells, which can then be tracked over time and space.

Importantly, the researchers show that the antibody treatment does not lead to loss of the leukocytes, which is important for allowing prolonged imaging of cell behavior. This makes CD45 antibodies a very useful tool for live imaging, and it sets the stage for the development of other antibody-based labels that can be used to target specific immune cell subsets.

Read the Gold Open Access article by L.D. Faulhaber et al., “Antibody-based in vivo leukocyte label for two-photon brain imaging in mice,” Neurophotonics 9(3), 031917 (2022), doi 10.1117/1.NPh.9.3.031917. The article is part of a Neurophotonics Special Section on Imaging Neuroimmune, Neuroglial, and Neurovascular Interfaces, guest edited by Andy Shih, Kıvılcım Kılıç, and Vanessa Coelho-Santos.

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