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Aby Joseph, Colin J Chu, GUANPING FENG, Kosha Dholakia, Jesse B Schallek; Label-free adaptive optics imaging of single immune cells and vascular response in retinal inflammation. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1132.
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© ARVO (1962-2015); The Authors (2016-present)
Little is known about the cellular immune response of the central nervous system (CNS) as the brain is shrouded in highly scattering media (skull). While a craniotomy may assist, the very act of surgery and exogenous tagging of immune cells may alter cell behavior. Here we show the first label-free images of single immune cell dynamics and vascular response to inflammation in the living retina, a part of the CNS.
An intravitreal injection of lipopolysaccharide (LPS) induced acute ocular inflammation (Chu et al. 2016) in anesthetized C57BL/6J mice (N=6). Mice were imaged with custom phase-contrast (796 nm) adaptive optics scanning light ophthalmoscopy. Retinal venules, neighboring arterioles and intermediate neural parenchyma were imaged longitudinally at baseline and 6, 24, 72 and 240 hours post-injection. Cellular blood flow was quantified with 15 kHz linescan imaging (Joseph et al. 2019). Time-lapse imaging over tens of minutes revealed immune cell motility.
An infiltration of immune cells was seen by 6 hours post LPS injection. Motility of cells confirmed them to be circulating immune cells of myeloid origin, and not neurons or macroglia. Rolling of white blood cells (WBCs) along the venular wall was imaged; rolling speeds (0-14 µm/s) were far slower than RBC speeds (0.5-23.1 mm/s). Secondary to rolling, time lapse imaging showed WBCs extravasate through the vascular wall into the neural parenchyma (Fig. 1). Cell infiltration peaked at 24 hours post LPS injection, with inflammatory resolution within 240 hours. Blood flow in both arterioles and venules increased (58±9% at 24 hours), though remarkably, they achieved this in different ways. Venules increased flow by dilating (36±8% dilation at 24 hours, mean±SD) (Fig. 2). Arterioles did not dilate, but had increased velocity (49±31%), to facilitate conservation of flow. Vessels had reduced flow on 10th day (10±15% >baseline).
For the first time, single immune cell dynamics were imaged in the CNS inflammatory response, without contrast agents or surgery. Cellular blood flow response and rolling, trans-endothelial migration and parenchyma surveillance of WBCs were imaged. These biomarkers could be tracked longitudinally in the same animals to reveal progressive inflammation within hours and resolution within days. Excitingly, our label-free approach using safe NIR light suggests possible translation to humans.
This is a 2020 ARVO Annual Meeting abstract.
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