Requirements for Passage of T Lymphocytes Across Non-Inflamed Retinal Microvessels

Abstract

Abstract: : Purpose: To investigate the requirements for passage of T lymphocytes across the blood-retinal-barrier (BRB) to perform immune surveillance. Methods: Naive and in vitro concanavalin A (Con A) activated T cells were labelled with calcein-AM (C-AM) and adoptively transferred into syngeneic normal B10.RIII mice or human interphotoreceptor retinoid binding protein (IRBP) peptide immunized mice, 9 days post-immunization (pi), with experimental autoimmune uveitis (EAU). Cell movement in the retinal circulation was tracked using intravital microscopy. Infiltration of blast cells into the retina, breakdown of the BRB and expression of intercellular adhesion molecule-1 (ICAM-1) and P-selectin were evaluated in retinal whole mounts at different times after adoptive transfer of blast T cells using confocal microscopy. Results: Only activated T cells were able to penetrate the normal BRB. A minimum number (≥ 1× 10⁵ cells/mouse) of Con A-activated blast T cells needed to be adoptively transferred before lymphocytes could cross the normal BRB. In vitro Con A-activated T cells could cross a disabled BRB, in a mouse with EAU, within one hour, whereas 8-16 hours were needed for them to penetrate a normal BRB. This passage of activated blast cells across the breached BRB, occurred more quickly and more extensively than for the naive T cells. Cell rolling and reduction of shear stress did not occur in normal retinal venules and post-capillary venules, only in those of IRBP-peptide immunized mice at day 9 pi. In normal recipient mice, neither adoptive transfer of Con A blast cells nor naïve cells changed the hydrodynamic factors. However, in mice that had been pre-treated with Con A blast cells 24 hours earlier, the population of slow-moving cells (3-5 mm/s) increased significantly compared to that in untreated recipient mice. Adoptive transfer of 10⁷ Con A blast cells induced limited and transient breakdown of the BRB and up-regulation of the adhesion molecule ICAM-1. Conclusions: Only activated T lymphocytes are able to cross the non-inflamed BRB and enter the neuroretina and this is only after the activation of vascular endothelial cells. Up-regulation of ICAM-1 and breakdown of the vascular endothelial barrier is required and is likely to be induced by activated lymphocytes themselves over a period of 8-16 hours.

Keywords: retina • pathology: experimental • inflammation