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L.C. Hooper, M.S. Chin, B. Detrick, J.J. Hooks; Alterations in TNF– receptor signaling in Experimental Coronavirus Retinopathy . Invest. Ophthalmol. Vis. Sci. 2004;45(13):565.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Experimental coronavirus retinopathy (ECOR) is a retinal degeneration model system that is triggered by a virus and is composed of a genetic and autoimmune component. Preliminary studies indicated that both TNF–α and soluble TNFRs are elevated in virus–infected retinal degeneration susceptible BALB/c mice. The purpose of this study was to characterize alterations in downstream signaling molecules, such as NO (nitric oxide). Methods: Mice were injected intravitreally with 5 µl of media or with MHV, strain JHM at a concentration of 1.3 x 106 pfu/ml. Eyes were collected at varying times after inoculation. Eyes were dissected and retinas removed for mRNA isolation followed by RT–PCR for iNOS (inducible nitric oxide synthase). Mononuclear cells were isolated and release of sTNFR2 was evaluated by ELISA. Production of iNOS and NO was measured in the presence or absence of sTNFR2. Results: During the acute phase of the infection, at day 4 and 8, mRNA levels of iNOS were only detected within retinas of infected animals and not in control or mock–injected animals. Gene expression of iNOS decreased from day 4 to 8 in BALB/c mice, while it increased in CD–1 mice during this time period. These studies indicate that NO production was down regulated in BALB/c mice at day 8, a critical time point for the conversion from inflammatory disease to retinal degeneration. We next performed in vitro studies to determine the source of sTNFR2 and its effect on TNF–α receptor signaling. The adherent cell population of mononuclear cells from BALB/c mice released significantly more sTNFR2 (p< 0.0005) than did these cells from CD–1 mice. Incubation of mouse macrophages with TNF–α and IFN–γ augmented NO production. The presence of sTNFR2 significantly (p<0.01) inhibited this TNF–α receptor signaling in monocyte cell cultures. Conclusions: These studies demonstrate that retinal degeneration in ECOR is associated with up regulation of TNF–α and sTNFR2 combined with the down–regulation of NO. It is possible that the high levels of sTNFR2 decrease NO production within the retina and this shift may alter Th1 responses and thereby the autoimmune component of this retinal degenerative disease.
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