Interferon gamma immunoreactivity in iris nerve fibres during endotoxin induced uveitis in the rat

Expression of toll-like receptor 4 in uvea-resident tissue macrophages during endotoxin-induced uveitis

PURPOSE

To investigate the dynamics and distribution of toll-like receptor 4 (TLR4)-positive cells and resident tissue macrophages in the uvea during endotoxin-induced uveitis (EIU) in Wistar rats.

METHODS

Wistar rats (n=40) received a footpad injection of 200 microg of Vibrio cholera lipopolysaccharide (LPS), and the intensity of anterior segment inflammation was evaluated after the LPS injection. Ten rats each were killed 6, 12, 24 and 48 h after injection. Ten normal Wistar rats were killed as controls (0 h). The iris-ciliary body complex and choroids from each eye were removed and subdivided into segments. Immunohistochemical localization of TLR4 and a resident tissue macrophage marker, cluster of differentiation 163 (CD163), was performed on whole mount isolated iris-ciliary body complexes and choroids. TLR4+ and CD163+ cells in the iris were manually counted, and the cell density (cells/mm(2)) was calculated. The distribution patterns and phenotypes of cells expressing these two proteins were further characterized by double-labeled immunofluorescence studies.

RESULTS

The iris-ciliary body complex did not express TLR4 in normal rats. TLR4+ cells were detectable in the iris stroma 6 h after injection, and the number significantly increased (p<0.001 by one-way ANOVA) 12, 24, and 48 h after injection. The morphology of TLR4+ cells hardly changed 12-48 h after injection. CD163 was expressed in the uvea in all rats. During the inflammatory response phase (0-48 h after injection), the proportion of CD163+ tissue macrophages having a round morphology increased (p<0.001 by one-way ANOVA) concurrently with a decrease in the proportion of dendritiform CD163+ cells. These changes occurred mainly in the macrophages located in the stroma bordering the iris endothelial layer. Double-labeling immunofluorescence demonstrated the co-expression of TLR4 and CD163 in round stroma cells with TLR4 located at the cell membrane and CD163 in the cytoplasm. TLR4+ cells could not be detected in choroids in any of the rats.

CONCLUSIONS

The results of the present study indicate that TLR4 expression increased in the iris and iris tissue macrophages expressed TLR4 during EIU. This has significant implications for the understanding of ocular inflammation and for interpreting the potential role of Gram-negative bacteria in the pathogenesis of acute anterior uveitis.

Induced autoimmunity to heat shock proteins elicits glaucomatous loss of retinal ganglion cell neurons via activated T-cell-derived fas-ligand

Glaucomatous optic neuropathy causes blindness through the degeneration of retinal ganglion cells (RGCs) and their axons, which comprise the optic nerve. Glaucoma traditionally is associated with elevated intraocular pressure, but often occurs or may progress with intraocular pressure in the normal range. Like other diseases of the CNS, a subset of glaucoma has been proposed to involve an autoimmune component to help explain the loss of RGCs in the absence of elevated intraocular pressure. One hypothesis involves heat shock proteins (HSPs), because increased serum levels of HSP autoantibodies are prominent in some glaucoma patients with normal pressures. In the first direct support of this hypothesis, we found that HSP27 and HSP60 immunization in the Lewis rat induced RGC degeneration and axon loss 1-4 months later in vivo in a pattern with similarities to human glaucoma, including topographic specificity of cell loss. Infiltration of increased numbers of T-cells in the retina occurred much earlier, 14-21 d after HSP immunization, and appeared to be transient. In vitro studies found that T-cells activated by HSP immunization induced RGC apoptosis via the release of the inflammatory cytokine FasL, whereas HSP immunization induced activation of microglia cells and upregulation of the FasL receptor in RGCs. In summary, our results suggest that RGC degeneration in glaucoma for selected individuals likely involves failed immunoregulation of the T-cell-RGC axis and is thus a disturbance of both proapoptotic and protective pathways.

NK1.1 Cells Downregulate Murine Endotoxin-Induced Uveitis Following Intraocular Administration of Interleukin-12

To evaluate the role of IFN-gamma (interferon gamma) in IL-12- (interleukin-12)-induced inhibition of the inflammatory response in the eye during endotoxin-induced uveitis (EIU). C57BL/6 wild type mice and IFN-gamma-deficient (GKO) mice were injected with 250 microg of Salmonella typhymurium endotoxin as a model for EIU. Animals were then injected intraocularly with 100 ng of rIL-12 or the equivalent volume of Phosphate-buffer saline (PBS). Histopathologic grading of disease was performed 12, 36 and 72 h after endotoxin injection. Chemokine mRNA expression in the eye was evaluated by reverse transcriptase-polymerase chain reaction. Depletion of NK1.1+ cells in vivo was performed using a PK136 antibody. Depletion of IFN-gamma was performed using the R4-6A2 antibody. C57BL/6 mice treated with rIL-12 intraocularly were protected from the development of EIU. Neutralization of IFN-gamma with a monoclonal antibody abrogated such protection. The IL-12 protective effects were lost in NK1.1-depleted mice. Intraocular IL-12 decreased the expression of keratinocyte-derived chemokines (KC) gene but had no effect on macrophage inflammatory protein (MIP-2) gene. The protective effect of IL-12 during EIU occurs through production of IFN-gamma by NK1.1+ cells. IL-12-induced higher levels of IFN-gamma are also correlated with lower expression of the chemokine KC, resulting in diminished attraction of neutrophils to the inflammatory site.

T-bet expression in the iris and spleen parallels disease expression during endotoxin-induced uveitis

BACKGROUND

T lymphocytes have been implicated in the development of endotoxin-induced uveitis (EIU). T-bet is a Th1 cell-specific transcription factor that is involved in differentiation and effector functions. The aim of this study was to investigate kinetics of T-bet expression at the mRNA and protein levels during EIU using real-time PCR and whole-mount immunohistochemistry.

METHODS

A single footpad injection of 200 mug of lipopolysaccharide (LPS) was administered to male Wistar rats in order to induce EIU. Clinical changes were followed by slit-lamp examination. The expression of T-bet mRNA in the spleen was evaluated 0, 8, 16, 24, 48, and 96 h after LPS injection using real-time PCR. Immunohistochemistry was performed on the iris whole-mounts as well as on frozen sections of the spleen to evaluate T-bet protein expression. Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) was performed on the iris whole-mounts to assay apoptotic cells.

RESULTS

Uveitis was observed in all rats that received LPS. T-bet(+) cells and TUNEL(+) cells in the iris whole-mounts showed a similar pattern in cell number and distribution and both types of cells were observed at 8 h, significantly increased 24 h, and decreased 48 h after LPS injection. T-bet expression at both the mRNA and protein levels in spleen also paralleled ocular inflammation. It was weakly detectable after 0 h, increased after 8 h (index 1.3, T-bet(+) cells OD 17.43+/-2.15), reached its peak after 24 h (index 4.00, OD 53.52+/-4.00), and decreased 48 h following LPS injection (index 1.38, OD 25.75+/-2.45).

CONCLUSIONS

The results show that T-bet expression in both the iris and the spleen, and in apoptotic cells in the iris parallel the severity of intraocular inflammation after systemic LPS administration. These results suggest that T-bet may play a significant role in the dynamics of EIU.