Abstract
Purpose: :
Anterior chamber associated immune deviation (ACAID) is a model for studying mechanisms of immune privilege. The purpose of this project was to study if and why immune privilege is compromised post–retinal laser burn (RLB). In particular we examined, in vitro and in vivo, the effect of RLB on ocular immune privilege in the anterior chamber, (ACAID). We postulated that a laser burn to the retina would affect the ability of the anterior chamber to induce tolerance to a.c.–inoculated antigen.
Methods: :
A diode laser (wave length 810 nm, diameter 200 nm, power 50 mW, duration time 50 ms) was used to deliver four spot burns to the right retina of B6 mice. The retina tissue was examined by light microscopy (HE staining) at various times (1, 4, 7, 14, 21days (D)) after RLB, ACAID was induced by a.c.–inoculation of OVA (50 µg/2 µl) and immunized 7D later with OVA/CFA. To test for delayed hypersensitivity (DH), mice were challenged 7D later in the ear pinnae with OVA–pulsed peritoneal exudates cells (PEC: 2x 105) and ear swelling was measured after 24 hours. The aqueous humor (AqH), AqH was collected from 10 eyes at various time points post burn.
Results: :
The quality of the burn was observed, by histological examination, destruction of outer nuclear layer (ONL), photoreceptor segment, Bruch’s membrane and retinal pigment epithelium (RPE) followed the laser burn. We also saw dilation of choroid vessels and infiltrating inflammatory cells in the ONL 1D post burn. Also, RPE appeared to move toward the ONL, while other RPE around the laser burn lost their pigment. As early as 6 hours post laser burn and as late as 21D, antigen inoculation into the anterior chamber failed to induce ACAID induction in both the eye that received the RLB and the contralateral eye. Not only was ACAID induction suppressed in the eyes post burn but the inoculation of antigen into the anterior chamber induced an immune response. Unlike AqH from eyes of unmanipulated mice, in vitro analyses of the AqH samples harvested 24 hours post RLB from both the burned and non burned eye were unable to down regulated the expression of CD40 on thioglycolate induced PEC.
Conclusions: :
Since laser burn to the back of the eye affects the immune privilege in front of eye the possibility arises that the posterior eye is a major source of the immunosuppressive factors in the AqH. Alternatively because the non–burned eye also lost immune privilege, we postulate that the RLB damage to neural fibers or neurons plays a major role in the loss of ACAID.
Keywords: ACAID • laser • retina