Apoptosis of CD4+ T cells occurs in experimental autoimmune anterior uveitis (EAAU)

Expressions of lymphotactin and its receptor, XCR, in Lewis rats with experimental autoimmune anterior uveitis

BACKGROUND

To demonstrate the expression of lymphotactin and its receptor (XCR) in the iris/ciliary body and popliteal lymph node, and to clarify their roles in experimental autoimmune anterior uveitis (EAAU).

METHODS

Uveitis was induced in Lewis rats by injection of melanin-associated antigen into the peritoneum and footpad. At defined time points, mRNA expression levels of lymphotactin and XCR in the iris/ciliary body and popliteal lymph node were measured by semiquantitative polymerase chain reaction. Lymphotactin levels in aqueous humor and serum after immunization were determined by enzyme-linked immunosorbent assay. In a separate experiment, an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC; 200 mg/kg/day), was injected daily into the intraperitoneum after immunization. Cellular sources of lymphotactin were determined by immunhistochemical staining and flow cytometry.

RESULTS

Lymphotactin mRNA was upregulated in the iris/ciliary body with a peak level at day 14, which is in line with the disease course. XCR mRNA was expressed maximally and then declined gradually from days 5 to 21. With an expression pattern similar to that of mRNA expression, lymphotactin in aqueous humor had attracted corresponding numbers of leukocytes. PDTC markedly inhibited the expression of lymphotactin in aqueous humor and serum. Immunohistochemical staining and flow cytometry analysis revealed that the expression of lymphotactin was detected in infiltrated inflammatory cells, dominantly CD8+ T cells, and increased along with inflammation.

CONCLUSIONS

The lymphotactin and XCR interaction might direct distinct lymphocytes subsets to inflammatory sites. Lymphotactin could regulate the inflammatory process. Lymphotactin expression may be modulated, at least in part, through the NF-κB signaling pathway.

Inhibition of T cell apoptosis in the aqueous humor of patients with uveitis by IL-6/soluble IL-6 receptor trans-signaling

A fundamental mechanism of immune privilege in the eye is the induction of T lymphocyte apoptosis. Intraocular inflammation in uveitis implies compromise of immune privilege. This study sought to determine whether apoptosis of T cells is actively inhibited in patients with uveitis and by what pathways this may occur. Apoptotic lymphocytes were found to be absent from aqueous humor (AqH) of virtually all patients with recent-onset uveitis. However, T cells removed from the eye were highly susceptible to both spontaneous and Fas ligand-induced apoptosis in vitro. AqH from patients with uveitis had no modulatory effect on Fas ligand-induced apoptosis, but strongly suppressed survival factor deprivation-induced apoptosis. In contrast, noninflammatory AqH from patients undergoing cataract surgery had no modulatory effects on apoptosis at all. These data suggest that triggering of the Fas pathway is diminished in uveitis, and also that homeostatic resolution through survival factor deprivation-induced apoptosis is inhibited by factors present in AqH. The most widely recognized pathways, common gamma-chain cytokines and type I IFNs, did not contribute to AqH-mediated T cell survival. High levels of both IL-6 and soluble IL-6R were found in AqH. IL-6 alone did not induce T cell survival, because IL-6R expression on T cells in AqH was too low to facilitate signaling. However, combinations of IL-6 and soluble IL-6R were highly effective inhibitors of T cell apoptosis, suggesting that the trans-signaling pathway is likely to be a key mediator of T cell apoptosis inhibition mediated by uveitis AqH.

Resistance of lymphocytes to Fas-mediated apoptosis in Behçet's disease and Vogt-Koyangi-Harada syndrome

BACKGROUND

Behçet's disease and Vogt-Koyanagi-Harada (VKH) syndrome are characterized by a severe intraocular inflammation with a long course and recurrent episodes. Activated autoreactive lymphocytes are considered to be responsible for the development of this inflammation. These lymphocytes may also be involved in the perpetuation and recurrence of this inflammation if they do not properly go into apoptosis. To investigate this hypothesis, a study was carried out to evaluate the resistance of lymphocytes to apoptosis in these two uveitis entities.

METHODS

Blood samples were obtained from 17 patients with Behçet's disease, 15 patients with VKH syndrome, and 11 healthy individuals. Mononuclear cells were isolated by centrifugation with Ficoll-Paque and cultured in RPMI 1640 with or without phytohemagglutinin (PHA) for 9 h at 37 degrees C in an atmosphere with 5% CO( 2). The obtained cells were incubated with anti-Fas antibody for 8 h at 37 degrees C in an atmosphere with 5% CO(2). The cells were stained with annexin V/propidium iodide and finally subjected to flow cytometry.

RESULTS

A significantly lower percentage of apoptotic lymphocytes after PHA stimulation was noted in Behçet's disease (19.7 +/- 4.1%) and VKH syndrome (20.4 +/- 6.9%) than in controls (26.1 +/- 7.3%). The percentage of apoptotic lymphocytes without PHA stimulation also tended to be lower in the patients with Behçet's disease (12.6%) and with VKH syndrome (12.8%) than in controls (14.6%), although the difference was not significant.

CONCLUSION

Lymphocytes in patients with either Behçet's disease or VKH syndrome are relatively resistant to apoptosis mediated by anti-Fas antibody. These apoptosis-resistant, or long-lived, lymphocytes may be involved in the chronic and recurrent intraocular inflammation seen in these patients.