T CELL MEDIATED AUTOIMMUNE TARGETING OF THE ASTROCYTIC ENDFOOT PROTEIN AQP4 LEADS TO NEURONAL/AXONAL SWELLING BUT NOT CELL LOSS IN THE RETINA

Abstract

Purpose : Glial cells constitute a majority of cells of the CNS and play a significant supportive role in maintaining neuronal function and survival. Targeted autoimmune mediated injury of different glial populations appears to result in different clinical disease phenotypes. While targeting oligodendrocytes via MOG results in neuronal loss, we describe here the surprising reversible pattern of injury seen with targeting AQP4 which is found on the astrocytic end feet surrounding vascular endothelium.

Methods : We induced optic nerve (ON) inflammation in female C57Bl/6J wild-type (WT) recipient mice by Th17-polarized AQP4 p201-220-specific (n=5) or MOG p35-55-specific T cells (n=5), using 5 sham-immunized mice as controls. We monitored and compared clinical severity scores and inner retinal layer (IRL) thickness obtained from Spectral Domain OCT volume scans throughout the course of disease. ONs from representative mice of all groups were stained for inflammation, demyelination, and neuronal/axonal injury. After two weeks, ganglion cells (GC) on retinal whole-mount were stained for Brn3a and quantified.

Results : All AQP4 and MOG-immunized mice developed paralysis. Onset of disease induced by AQP4 p201-220-specific T cells occurred earlier and, in contrast with EAE induced by WT MOG-specific T cells, recovery was complete. In AQP4-immunized mice, IRL thickness increased parallel to the clinical disease course, with complete return of IRL thickness to baseline upon recovery. Retinal whole-mount staining demonstrated preservation of GC. In contrast, mice that received MOG-specific T cells exhibited persistent clinical disease, which was associated with progressive IRL thinning (66±0.53 vs. 72±1.04 µm in controls at day 14, P<0.001) and loss of GC (1,847±157 vs. 4,292±110 GC/mm², P<0.001). AQP4-specific T cells caused ON inflammation characterized primarily as a perineuritis. In contrast, MOG-specific T cells induced severe optic neuritis.

Conclusions : AQP4-specific T cells can enter the CNS to initiate clinical and histologic CNS disease, but are not sufficient to cause permanent damage. Retinal OCT can be used as a surrogate for CNS injury and neuronal loss in MOG and AQP4-targeted CNS autoimmunity in mice. Our models provide evidence that T cell mediated injury is not the basis for the tissue destructive pattern of damage seen in neuromyelitis optica.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.