Abstract
Inflammation in vascularized tissues is mediated by circulating immune cells that are recruited to damaged tissue. Immune cells undergo dramatic changes in speed and motility indicating the severity and staging of inflammation. Here, we characterize the spectrum of retinal leukocyte kinetics in response to an acute inflammatory stimulus using adaptive optics scanning light ophthalmoscopy (AOSLO) in living mice.
C57BL/6J male mice were injected intravitreally with 1 µL lipopolysaccharide (LPS) and imaged at 6, 24 and 72 hours after LPS injection using phase contrast and fluorescence AOSLO. Speed of circulating leukocytes (n= 286 cells, 2 mice) was measured with 15kHz point-scan imaging using automated approach (Joseph et al. 2019). Rolling leukocytes (n=300 cells, 5 mice, 6 hrs after LPS) and extravasated cells (n=92 cells, 8 mice) were visualized with time-lapse imaging and manually tracked using ImageJ.
Using our custom AOSLO, we observed leukocyte speeds spanning 5 orders of magnitude in the living retina. The fastest speeds were the circulating leukocytes (13,257.37 ± 7,086.41 µm/s). After LPS, leukocytes roll along the venular wall, where cell speed was 1000x slower (11.45 ± 7.45 µm/s.) When immune cells extravasated into the tissue, cell speed dropped further by 100x (0.3 ± 0.15 µm/s).
Observed leukocyte speeds cluster around three distinct velocity bands that stratify the unique and purposeful behavior of these cells as they progress through the inflammatory cascade.
Funding: Funding: NIH Grant R01 EY028293, P30 EY001319, Career Development Award, Career Advancement Award (Schallek) and Unrestricted Grant to the University of Rochester Department of Ophthalmology from Research to Prevent Blindness, New York, New York , and a research collaboration grant from Genentech Inc.