Background
Neuroinflammation is generally defined as the response of brain cells to infection and other sources of cell death, involving infiltration of circulating immune cells to the brain.
Neutrophils are commonly known as the earliest responders to acute inflammation, aiding the initiation and continuation of immune reactions throughout the human body. In particular, during neuroinflammation, neutrophils participate in the general immune response by signaling to diverse cell types, including endothelial cells, mesenchymal stem cells, lymphocytes, and microglia.
The IntraVital Two-photon Microscope System : IVM-M was used to observe the effects of lipopolysaccharide (LPS)-induced neuroinflammation on neutrophils and microglia within brain tissue of live mice.
Method
Two weeks before intravital imaging, cranial window surgery of LysMGFP/+ mice was performed. Intravital imaging was performed at 6 h after LPS injections for 2 consecutive days.
LysMGFP/+ mice have the lysozyme gene replaced by green fluorescent protein (GFP) and this is used for the visualisation of neutrophils. After performing mouse tail vein intravenous injections of Texas red dextran to label the blood vessels, a laser scanning intravital two-photon microscope (IVM-M, IVIM Technology) was used to perform two-color imaging.
Results
Imaging results below show two examples of neutrophils returning to the vessel after cross-talk with Microglia during LPS induced neuroinflammation. Reverse-transendothelial migration of neutrophils in inflamed brain parenchyma can be followed in this manner.
The IVIM-M intravital microscope is ideal for live cell in vivo imaging of animal models. As a purpose-built system, the tuneable two-photon imaging system with ultrafast scanning and uniform illumination at scan rates up to 100fps @512×512 pixels produces high-quality images in real-time. Furthermore, with integrated anesthesia capabilities and body temperature monitoring and automated regulation combined with animal motion stabilisation (highly suited to abdominal organ imaging) this system is a true turnkey solution suitable for imaging any mouse organ and the shedding light on human diseases and treatments.
Summary
Using IVIM Tech’s IVIM-M two photon intravital microscope, researchers have been able to directly observe the effects of neutrophils and microglia on mouse brains undergoing LPS-induced neuroinflammation in real-time. Using this technique researchers have observed various changes in neutrophils and microglia, specifically neutrophil infiltration and increased levels of movement within the brain tissue. Perhaps most interestingly, neutrophils were observed to have actively interacted with microglial processes as well as exhibiting reverse transendothelial migration (rTEM) back to the bloodstream.
For more details on this study, please refer to “Neutrophils Return to Bloodstream Through the Brain Blood Vessel After Crosstalk With Microglia During LPS-Induced Neuroinflammation“, by Kim et al. (2020), published in Frontiers in Cell and Developmental Biology.