Hematopoietically derived retinal perivascular microglia initiate uveoretinitis in experimental autoimmune uveitis

BACKGROUND

Hematopoietically derived cells in the retina were studied for the expression of molecules associated with antigen presentation.

METHODS

Bone marrow cells of (Lewis x Brown Norway) F1 rats (LBNF1) were transplanted to sublethally irradiated Brown Norway (BN) rats to construct chimeric rats (LBNF-->BN). Each of 21 established chimeras received an adoptive transfer of uveitogenic Lewis T lymphocytes. Three rats were killed on each of 7 consecutive days. The right eye of each rat was processed for flat-mount preparation of the retina; the left eye of each was frozen for cryostat sectioning. All tissues were then stained with one of the following antibodies: OX-3 (Lewis-specific MHC class II marker), anti-ICAM, anti-B7- 1, anti-TNF-alpha or anti-IL-1beta.

RESULTS

Initial clinical signs of EAU appeared first on day 4; by day 6, full-blown EAU was noted. The flatmount preparations revealed the presence of OX-3+ cells in the retina, perivascularly exhibiting dendritic morphology on day 2. These cells were observed in the retinal nerve fiber layer (NFL). No B7-1+, ICAM-1+, TNF-alpha+ or IL-1beta + cells were detected. Cryostat sections revealed positive cell staining of perivascular microglia and astrocytes in the retinal NFL with anti-IL-1beta and anti-TNF-alpha antibodies.

CONCLUSIONS

Since only perivascular bone marrow-derived cells are seen to express MHC class II molecules prior to onset of EAU, and since these cells also generate the cytokines IL- 1beta and TNF-alpha, it appears that initial presentation of antigen in the retina could be by these cells.

Copolymer 1 inhibits experimental autoimmune uveoretinitis

Copolymer 1 (Cop 1) inhibits experimental allergic encephalomyelitis induced by a variety of myelin proteins, but has been found ineffective so far in inhibiting other experimental autoimmune diseases such as diabetes or arthritis. Here, we report for the first time that Cop I inhibits the development of experimental autoimmune uveoretinitis, induced in mice by interphotoreceptor retinoid-binding protein (IRBP). Pooled data of three experiments showed that treatment with Cop 1, at 0.5 mg/mouse, reduced the disease severity by 53% ( p = 0.0002). Cop 1 treatment also inhibited the proliferation and the production of cytokines by lymph node cells in response to IRBP and moderately reduced the antibody response to this antigen. The possible mechanisms of EAU inhibition by Cop 1 are discussed.

Effects of FTY720, a novel immunosuppressant, on experimental autoimmune uveoretinitis in rats

The immunosuppressive properties of FTY720, a novel immunosuppressant obtained by structural modification of ISP-I isolated from the fermentation broth of Isaria sinclairii, were studied in experimental autoimmune uveoretinitis (EAU) in rats. Lewis rats were immunized with S-antigen and treated with FTY720 (0. 03, 0.06, 0.1 mg kg(-1)day(-1)) or distilled water for 16 days after the immunization. FTY720 suppressed the incidence and intensity of EAU in a dose-dependent manner as demonstrated by clinical and histological examinations. The drug significantly suppressed the serum levels of antibodies to S-antigen and antigens-specific lymphocyte proliferation. The number of peripheral lymphocytes, but not neutrophils, was markedly reduced by FTY720 treatment. FTY720 also suppressed the intensity of EAU when it was given from the day of EAU onset. These results indicate that FTY720 has intense immunosuppressive effects on EAU in rats and may be a potential candidate for use in the treatment of patients with autoimmune uveitis.

Identification of a new epitope of human IRBP that induces autoimmune uveoretinitis in mice of the H-2b haplotype

PURPOSE

Experimental autoimmune uveoretinitis (EAU) is a T-cell-mediated disease induced by immunization with interphotoreceptor retinoid binding protein (IRBP). Major uveitogenic sites have been identified for mice of the H-2r and H-2k haplotypes but not for the H-2b haplotype. The present communication describes the characterization of an epitope contained in residues 1 to 20 of human IRBP that induces EAU in H-2b mice.

METHODS

H-2b (C57BL/6, 129/J) and H-2r (BIO.RIII) mice were immunized with peptide 1-20 or with whole (bovine) IRBP. EAU (histopathology) and immunologic responses (delayed-type hypersensitivity [DTH], lymphocyte proliferation, and cytokine production) were assessed after 21 days.

RESULTS

C57BL/6 mice, 129/J and (129/JxC57BL/6)F1 mice, immunized with 200 to 300 microg of peptide, developed DTH and EAU with scores comparable to those induced by 100 microg IRBP. Their lymphocytes proliferated to the peptide and produced interferon-gamma (but not interleukin-4) and transferred EAU to syngeneic recipients. Lymphocytes of IRBP-immunized mice also responded to the peptide. Peptide 1-20-immunized B1O.RIII mice failed to develop either disease or immunologic responses. CONCLUSIONS. Human IRBP peptide 1-20 contains a major epitope for the H-2b haplotype, which is apparently not presented by the H-2r haplotype.

The role of costimulatory molecules B7-1 and B7-2 in mice with experimental autoimmune uveoretinitis

BACKGROUND

Onset of experimental autoimmune uveoretinitis (EAU) is believed to involve a CD4-positive type 1 T helper cell (Th1) immune response, with inhibition involving a Th2 immune response. Development of Th1 and Th2 responses involves the participation of the costimulatory molecules B7-1 and B7-2, respectively. The purpose of this study was to investigate the role of B7-1 and B7-2 in the EAU model in mice.

METHODS

B10.A mice were immunized with interphotoreceptor retinoid-binding protein (IRBP) and given daily intraperitoneal injections of either phosphate-buffered saline (control), mouse monoclonal antibody (mAb) to B7-1, mAb to B7-2, or mAb to both B7-1 and B7-2. Eyes were evaluated by histopathological criteria and cytokines were assayed in culture medium of IRBP-stimulated lymphocytes. Cellular immune responses were measured by cell proliferation assay under IRBP stimulation.

RESULTS

Rates of EAU onset were 5/10 (50%) for control mice, 1/9 (11%) for mice treated with anti-B7-1 mAb, 5/6 (83%) for mice treated with anti-B7-2 mAb, and 2/6 (33%) for mice treated with both anti-B7-1 and anti-B7-2 mAb. Mean histopathological severity scores were 2. 4+/-0.8, 1.0+/-0, 2.6+/-1.0, and 1.0+/-0, respectively. Production of IL-5 was significantly increased in mice treated with anti-B7-1 mAb, while IFN-gamma was increased in mice treated with anti-B7-2 mAb. Spleen cell proliferation was significantly reduced in mice treated with anti-B7-1 mAb.

CONCLUSIONS

These results suggest that the costimulatory molecules B7-1 and B7-2, via their influence on generating Th1 and Th2 immune responses, play an important role in the clinical outcome of EAU in mice immunized with IRBP.

The requirement for pertussis to induce EAU is strain-dependent: B10.RIII, but not B10.A mice, develop EAU and Th1 responses to IRBP without pertussis treatment

PURPOSE

Experimental autoimmune uveoretinitis (EAU) in mice is an important model for elucidating basic mechanisms in autoimmune eye disease. The need for pertussis toxin (PTX) as an additional adjuvant to elicit EAU has limited the usefulness of this model in some types of studies by introducing a pleiotropic factor with confounding effects on the immune response.

METHODS

In the present study the authors examined the ability of B10.RIII mice, the most susceptible strain known so far, to develop EAU in response to the retinal antigen, interphotoreceptor retinoid-binding protein (IRBP), and to a major uveitogenic epitope of IRBP, peptide (p)161-180, in the absence of PTX treatment.

RESULTS

The data indicate that high disease scores in response to IRBP and p161-180 were found in B10.RIII mice, without the need for PTX as part of the immunization protocol. Unlike the B10.A strain in which appreciable disease did not develop without PTX, B10.RIII mice mounted a high IFN-gamma response to IRBP in the absence of PTX treatment. Interestingly, and unlike the effect with IRBP, in vitro recall response to p161-180 was low in IFN-gamma, despite good EAU scores.

CONCLUSIONS

The data indicate that an important mechanism through which PTX facilitates induction of cell-mediated autoimmunity is by promoting a Th1 polarization of the immune response. The propensity of B10.RIII mice to mount a more polarized Th1 response to IRBP than other strains may contribute to their ability to develop EAU without pertussis adjuvant. Nevertheless, the induction of EAU by p161-180 in the context of a relatively limited IFN-gamma production indicates that non-Th1- and Th-related mechanisms are likely to act in concert to determine the outcome of disease.

Cytokines and apoptotic molecules in experimental melanin-protein induced uveitis (EMIU) and experimental autoimmune uveoretinitis (EAU)

The cytokine profile and occurrence of apoptosis during experimental melanin-protein induced uveitis (EMIU) were investigated and compared with that of experimental autoimmune uveoretinitis (EAU). EMIU or EAU was induced in Lewis rats. Eyes were collected at different time points after immunization. Cytokine mRNA expression was identified in the inflammatory cells in the uvea of EMIU rats; IL-2, IFN-gamma and IL-12 increased at the peak of the inflammation, and then tapered off as inflammation subsided. IL-4 and IL-10 increased at the peak of ocular inflammation, and persisted with inflammation resolved. Fas and FasL were expressed consistently in ocular resident cells of EMIU, but were elevated in EAU. In EAU, Bcl-2 expression showed a sharp peak in inflammatory cells but not in the resident cells. In EMIU, high levels of Bcl-2 were present and persisted in both ocular resident and inflammatory cells. Expression of Bax was relatively stable in both EAU and EMIU. Cellular DNA fragmentation was detected in the retinal glial cells of EAU and some inflammatory cells of EMIU. In EMIU, the dynamics of Th1 cytokines were consistent with the ocular inflammation, whereas persistent expression of Th2 cytokines was consistent with their known regulatory role. The continuous high expression of Bcl-2 and the high ratio of Bcl-2 to Bax in the eyes of EMIU may possibly contribute to prevention of ocular tissue damage, and of inflammatory cells from undergoing apoptosis, thus resulting in chronic recurrent inflammation.

Systemic expression of rat soluble retinal antigen induces resistance to experimental autoimmune uveoretinitis

To assess the role of sequestration in the maintenance of the immune privilege of the retina, retrovirally mediated gene transfer was used to express a defined, specific retinal autoantigen, rat soluble retinal Ag (S-Ag), in a systemic, nonsequestered manner. In this study we report the stable, long term transduction of rat retinal S-Ag into PBMC. Tolerance to S-Ag was assayed by challenging the S-Ag chimeric animals with S-Ag peptides in CFA and monitoring the time course and severity of experimental autoimmune uveoretinitis (EAU). The resulting data showed a correlation between the incidence of S-Ag chimerism and the loss of susceptibility to EAU. The development of resistance to EAU induction supports the hypothesis that Ag sequestration contributes to retinal immune privilege.

Effects of monoclonal antibodies directed at cell surface molecules on murine experimental autoimmune uveoretinitis

BACKGROUND

To elucidate the immunopathogenic mechanism of endogenous uveitis, the effects of monoclonal antibodies to molecules involved in the immune response were studied in murine experimental autoimmune uveoretinitis (EAU).

METHODS

Monoclonal antibodies to CD4, CD8, Ia(k), Ia(d), lymphocyte function-associated antigen-1 (LFA-1), and intercellular adhesion molecule-1 (ICAM-1) were used in this study. The monoclonal antibodies were added in the culture of lymph node cells from B10.BR mice(H-2(K)) immunized with interphotoreceptor retinoid-binding protein (IRBP) and the inhibition of proliferative response was measured. In vivo, IRBP-immunized mice were treated with a high dose of the antibody, and the EAU induction was examined both clinically and pathologically.

RESULTS

Proliferative response of IRBP-sensitized lymph node cells was inhibited strongly by anti-CD4 or anti-LFA-1 monoclonal antibody and moderately by anti-Ia(k) or anti-ICAM-1 monoclonal antibody. In contrast, no inhibitory effect of anti-CD8 or anti-Ia(d) monoclonal antibody was observed. In vivo treatment with anti-CD4 monoclonal antibody inhibited development of EAU in a dose-dependent manner, while in vivo treatment with other monoclonal antibodies did not cause significant suppression of EAU.

CONCLUSIONS

CD4, Ia, LFA-1, and ICAM-1 molecules play important roles in the antigen-specific immune response of lymphocytes. However, in in vivo treatment with monoclonal antibodies to these molecules, only anti-CD4 monoclonal antibody had a strong inhibitory effect on the development of EAU.

Effects of experimental ocular inflammation on ocular immune privilege

PURPOSE

To determine whether the inflammation of endotoxin-induced uveitis (EIU) and experimental autoimmune uveoretinitis (EAU) alters key in vivo and in vitro parameters of ocular immune privilege.

METHODS

For EIU induction, C3H/HeN mice received 200 microg lipopolysaccharide (LPS). For EAU induction, B10.A mice were immunized with 50 microg interphotoreceptor retinoid-binding protein (IRBP) mixed with complete Freund's adjuvant. Aqueous humor (AqH) was collected at periodic intervals and assayed for leukocyte content and the ability to suppress or enhance T-cell proliferation. Eyes with EAU were assessed for the capacity to support anterior chamber (AC)-associated immune deviation (ACAID) induction after injection of ovalbumin (OVA).

RESULTS

Inflammation within the anterior segment in EIU peaked at 12 to 24 hours and was detected from 10 days onward in EAU. In AqH of EIU, protein content rose within 4 hours, followed by infiltrating leukocytes. EIU AqH promptly lost its capacity to suppress T-cell proliferation and became mitogenic for T cells. In AqH of EAU, protein and leukocyte content rose at 11 days and continued to remain elevated thereafter. Whereas 11-day EAU AqH failed to suppress T-cell proliferation, AqH at later time points reacquired immunosuppressive properties. Injection of OVA into the AC of eyes of mice with EAU failed to induce ACAID.

CONCLUSIONS

The intraocular inflammation of EIU and EAU disrupted important parameters of immune privilege, ranging from breakdown of the blood- ocular barrier, to loss of an immunosuppressive microenvironment, to abrogation of ACAID. Because AqH from inflamed EAU reacquired the ability to suppress T-cell proliferation, the authors conclude that the capacity to regulate immune expression and inflammation can be a property even of inflamed eyes.

Retinal expression of a neo-self antigen, beta-galactosidase, is not tolerogenic and creates a target for autoimmune uveoretinitis

Recent studies revealing active mechanisms of immune privilege in neural tissues have diminished the putative role of passive tolerance. To examine the significance of Ag localization in the retina on immune privilege, the immune responses of transgenic mice expressing high and low levels of beta-galactosidase (beta-gal) in the photoreceptor cells of the retina were compared with those of normal mice and those of mice expressing moderate levels of beta-gal systemically. Immunization with beta-gal induced experimental autoimmune uveoretinitis indistinguishable from that induced by known photoreceptor cell autoantigens, including destruction of photoreceptor cells, in transgenic mice with high level retinal expression. Retinal expression had no apparent effect on the immune responses to beta-gal, showing that tolerance was not elicited by levels of retinal beta-gal sufficient to serve as a target for autoimmune disease. Mice with systemic expression exhibited reduced lymphoproliferative responses following immunization with beta-gal and did not develop autoimmune disease. T cells prepared from normal mice immunized with beta-gal transferred experimental autoimmune uveoretinitis to the transgenic mice with high level retinal beta-gal expression, but no disease was found in mice with systemic transgene expression under these conditions. The results of our experiments are most consistent with sequestration being the primary mechanism of retinal immune privilege. The results also show that beta-gal can serve as an immunopathogenic neural autoantigen, and that T cells raised by immunization of normal mice with a foreign Ag can be immunopathogenic in certain transgenic recipients.

Retinitis pigmentosa, Coats disease and uveitis

PURPOSE

To study the anamnestic immune response to retinal specific antigens of two patients suffering from a rare triad of retinitis pigmentosa, Coats disease and uveitis.

PATIENTS

17-year-old girl presented with an acute episode of panuveitis, and her 19-year-old brother suffered from chronic uveitis. On examination, both patients showed retinal vascular changes and subretinal exudations typical of Coats disease, with bone-spicule pigmentary changes as observed in retinitis pigmentosa.

RESULTS

All routine examinations were unrevealing. However, the peripheral lymphocytes from these two siblings gave a specific anamnestic response to retinal antigens in vitro. A stimulation index of 4.6 was obtained when the sister's lymphocytes were stimulated with interphotoreceptor binding protein, IRBP--during the acute stage of the uveitis. The brother's lymphocytes showed a stimulation index of 2.7 towards S-Ag during the chronic phase of his uveitic condition.

CONCLUSIONS

These results indicate that autoimmunity towards retinal antigens may play some role in specific types of retinitis pigmentosa. Whether these autoimmune reactions are a primary pathological mechanism or are secondary to the extensive destruction of the photoreceptor layer resulting from the retinitis pigmentosa remains debatable.

Intranasal administration of retinal antigens induces transient T cell activation and apoptosis within drainage lymph nodes but not spleen

Mechanisms of mucosal tolerance induction, including anergy/deletion and active suppression are frequently described as mutually exclusive; dependent upon nature, dose and route of antigen administration. We have previously described induction of low-dose tolerance with administration of retinal autoantigens via the nasorespiratory tract which is antigen-specific, suppresses both cell mediated immunity and ultimately tissue destruction in experimental autoimmune uveoretinitis (EAU) and is mediated by splenic-derived regulatory cells. The present data further shows that splenocytes or fractionated splenic T cells, which secrete IL-4 and IL-10 when stimulated with retinal antigen in vitro, and not regional drainage lymph node cells transfer tolerance to naïve animals. Analysis of apparent mechanistic differences shows that during intranasal antigen administration, the proportion of CD4(+)T cells within drainage lymph nodes increases, concurrent with a burst of IFN-gamma. Following subsequent antigen challenge, T cells downregulate alphabetaTCR expression and undergo apoptosis in regional drainage lymph nodes. An increase in functional Th2 cytokine activity was noted in both Con-A and retinal antigen stimulated lymph node cultures in tolerized animals. T cells from tolerized animals secreted IL-4, whereas IL-10 was secreted predominantly by the non-T cell population present equally in control and tolerized animals. Therefore, spleen derived regulatory cells which suppress Th1 responses and T cell deletion/apoptosis in regional drainage lymph nodes are mechanisms which co-exist in tolerant rats. Th2 cytokine production after immunization appears consequential to tolerance-induced Th1 suppression.

Protective effect of the type IV phosphodiesterase inhibitor rolipram in EAU: protection is independent of IL-10-inducing activity

PURPOSE

Experimental autoimmune uveoretinitis (EAU) is a cell-mediated model of retinal autoimmunity that is negatively regulated by interleukin (IL)-10. The antidepressant drug rolipram, a type IV phosphodiesterase inhibitor, enhances IL-10 production by monocyte/macrophages. The effect of rolipram on induction of EAU and its associated immunologic responses was investigated.

METHODS

Mice were challenged for EAU induction by immunization with the retinal antigen interphotoreceptor retinoid-binding protein (IRBP) or by adoptive transfer of uveitogenic T cells and were treated with rolipram. EAU severity and immunologic responses to IRBP were analyzed. In addition, the effect of rolipram added to the culture on antigen-driven responses of primed lymph node cells was tested.

RESULTS

Rolipram treatment from days -1 to 7 after immunization (afferent phase) was not protective, but severity of EAU was reduced to 50% by treatment from days 8 to 16 after immunization or when EAU was induced by adoptive transfer (efferent phase). Antigen-specific proliferation and interferon (IFN)-gamma production ex vivo by lymph node cells of protected mice were not reduced. However, the addition of rolipram directly to the culture suppressed IRBP-driven proliferation and IFN-gamma production by primed lymph node cells. Freshly explanted lymph node cells of treated mice showed inhibition of IFN-gamma mRNA but no parallel enhancement of IL-10 mRNA by quantitative polymerase chain reaction. Rolipram inhibited EAU in IL-10 knockout mice equally well compared with controls and suppressed their primed lymph node cells in culture.

CONCLUSIONS

Rolipram appears to inhibit the expansion and effector function of uveitogenic T cells, raising the possibility that it may be useful for treatment of established disease. Contrary to expectations based on in vitro studies, the protective effects in vivo appear to be independent of IL-10. The observation that suppression of antigen-specific responses is demonstrable only in the physical presence of the drug suggests that, in a clinical setting, continuous administration of rolipram might be needed to sustain its therapeutic effect.

Identification of genomic regions controlling experimental autoimmune uveoretinitis in rats

The present study attempts to identify specific genetic loci contributing to experimental autoimmune uveoretinitis (EAU) susceptibility in F2 progeny of resistant Fischer (F344/N) and susceptible Lewis (LEW/N) inbred rats. F2 progeny of F344/N x LEW/N inbred rats were immunized with the R16 peptide of interphotoreceptor retinoid-binding protein (IRBP). A genome-wide scan was conducted using 125 simple sequence length polymorphism markers in selected F2 animals that developed severe eye disease or remained unaffected to identify phenotype:genotype co-segregation. The F2 population (n = 1287) demonstrated a wide range of histologically assessed EAU scores (assessed on a scale of 0-4). The disease incidence and severity were not consistent with a simple Mendelian inheritance model. Of the F2 hybrid rats, 60% developed EAU, implying the existence of a potent susceptibility locus with incomplete penetrance associated with the LEW genome or a more complex polygenic model of inheritance. Two genomic regions, on chromosomes 4 and 12, showed strong genetic linkage to the EAU phenotype (P < 0.0016), suggesting the presence of susceptibility loci in these chromosomal regions. In conclusion, we have identified two genomic candidate intervals from D4Arb8 to D4Mit17 on chromosome 4 and from the chromosome end to D12Arb8 on chromosome 12, that appear to influence EAU susceptibility in LEW/F344 rats. Further analysis of these genomic regions may lead to identification of the susceptibility genes and to characterization of their function.

Kinetics of intraocular cytokines in the suppression of experimental autoimmune uveoretinitis by type I IFN

The systemic administration of IFN-alpha/beta was previously found to suppress inflammation in rats with experimental autoimmune uveoretinitis (EAU); however, an effect on the systemic immune response was not identified. In order to investigate an immunological basis for suppression at the intraocular level, rats immunized with interphotoreceptor retinoid-binding protein (IRBP) were administered daily intramuscular injections of 10(5) IU IFN-alpha/beta and cytokines were measured by ELISA in intraocular extracts prepared by ultrasonification at various timepoints throughout the course of EAU. In control EAU, intraocular concentrations of IFN-gamma were found to be non-detectable on day 8 before the onset of inflammation, significantly elevated on day 12 at peak inflammation (182+/-106 pg/ml), then non-detectable again on day 16 after inflammation had begun to subside. In contrast, intraocular IFN-gamma in IFN-alpha/beta-treated rats remained non-detectable or low at all timepoints. Measurement of intraocular IL-2 revealed no difference between the two groups of rats. Intraocular IL-4 concentrations were elevated in rats treated with IFN-alpha/beta, although this cytokine was also detected in the same range in controls as well as normal rats. Finally, intraocular IL-10 was non-detectable on day 8, significantly elevated at peak inflammation on day 12 (588+/-139 pg/ml), then decreased to low levels on day 16 in control EAU rats, while remaining non-detectable or low in IFN-alpha/beta-treated rats. These results suggest that acute inflammation in IRBP-induced EAU in rats involves both IFN-gamma and IL-10 at the local intraocular level, and that systemic administration of IFN-alpha/beta inhibits EAU via a mechanism that involves suppression of both cytokines.

Retinal immunopathology in horses with uveitis

BACKGROUND

Equine uveitis is a spontaneous disorder of horses that can serve as a model for the study of human uveitis. Although the initial presentation is that of an anterior uveitis, retinal involvement has been noted in some cases. We report here the immunohistopathology of retinas from horses with uveitis.

METHODS

Sections of eyes recovered from horses with naturally occurring uveitis and from Shetland ponies with experimental leptospira-induced uveitis were stained by hematoxylin and eosin for histopathological evaluation. Immunohistochemistry was used to evaluate retinas for MHC Class II antigen expression and infiltration of T and B lymphocytes.

RESULTS

Histopathological abnormalities in retinas from horses with uveitis ranged from minimal to total loss of retinal tissue. MHC Class II antigen-positive round and dendritiform cells were seen in these retinas, but were not seen in retinas from horses without uveitis. There was no significant reactivity noted in the retinal pigment epithelial cells or Muller cells. Numbers of MHC Class II antigen-expressing cells and T lymphocytes correlated with the extent of retinal histopathology. B lymphocytes were seen primarily in retinas from horses that were seroreactive for Leptospira interrogans serovar pomona. Retinas from ponies with experimental uveitis had changes similar to those from horses with spontaneous uveitis.

CONCLUSIONS

These results suggest that retinal pathology may be a primary immunological event in equine uveitis, provide evidence that leptospira-associated uveitis may be a distinct subset of equine uveitides, underscore the relevance of the study of equine uveitis to human uveitis, and support the plausibility of a post-infectious immunopathogenesis of some naturally occurring uveitides in both humans and horses.

Effect of type I interferon on experimental autoimmune uveoretinitis in rats

In order to establish a scientific basis for the potential use of type I interferons (IFNs) in clinical uveitis, we examined the effect of a preparation of IFN-alpha/beta on experimental autoimmune uveoretinitis (EAU). Lewis rats were immunized with bovine interphotoreceptor retinoid-binding protein (IRBP) and given daily intramuscular injections of 10(5) IU mouse natural IFN-alpha/beta. Intraocular inflammation was assessed by slit-lamp biomicroscopy and histopathological examination. Rats treated daily with IFN-alpha/beta starting on the day of IRBP immunization showed decreased intraocular inflammation as well as a slight delay in onset of inflammation when compared to control rats. This effect was also observed to a lesser extent in rats treated during either the induction phase of EAU only, or starting immediately after the onset of inflammation in the effector phase of EAU. Measurement of IRBP-stimulated splenocyte proliferation and serum anti-IRBP antibody subtypes did not reveal a significant difference between IFN-alpha/beta-treated rats and control rats. Measurement of cytokine production by IRBP-stimulated splenocytes in vitro showed significantly decreased TNF-alpha for IFN-alpha/beta-treated rats compared to control, but no difference for IFN-gamma, IL-2, IL-4, and IL-10. These results indicate that systemic administration of IFN-alpha/beta suppresses IRBP-induced EAU in rats, and suggest that such suppression may be mediated in part by a reduction in TNF-alpha production.

Antigen-presenting cells in experimental autoimmune uveoretinitis

The present study attempts to identify the antigen-presenting cells in the retina, utilizing bone marrow-transplanted chimeric rats. Two types of chimeras were used: one produced by transplanting bone marrow cells from F1 hybrids of Lewis and Brown Norway (BN) into sublethally irradiated Brown Norway rats (LBN/F1-->BN), followed by adoptive transfer of S-antigen-specific T cells obtained from Lewis rats; the second produced by transplanting bone marrow cells from BN rats into sublethally irradiated F1 hybrids (BN-->LBN/F1), followed by adoptive transfer of S-antigen-specific T cells obtained from F1 hybrids. As controls, Lewis, F1 hybrids and BN rats also received adoptive transfer of syngeneic uveitogenic T cell lines. All animals were killed on the seventh day after adoptive transfer and their eyes and pineal glands were analysed immunohistochemically, utilizing antibody directed against Lewis specific MHC class II molecules(OX-3). The analyses revealed the development of uveoretinitis and pinealitis in both types of chimeras and in the Lewis and F1 hybrid rats. BN rats did not develop uveoretinitis. OX-3-positive cells were found in the retina and the pineal glands of both types of chimeras, and in the Lewis and F1 hybrid rats but not in the BN rats. These cells in the retina expressed dendritic morphology and perivascular distribution. Retinal pigment epithelia, Müller cells and the vascular endothelia of both chimeras, the two strains, and the F1 hybrid rats did not demonstrate OX-3-positive staining. These results suggest that the bone marrow-derived cells in the retina and pineal gland may present S-antigen to T cells, initiating the cascade of uveoretinitis and pinealitis.

Oral tolerance in experimental autoimmune uveoretinitis: feeding after disease induction is less protective than prefeeding

Oral administration of antigen modulates subsequent immune responses raised by conventional subcutaneous priming. If experimental autoantigens are administered, subsequent induction of autoimmune diseases may be inhibited. However, feeding autoantigens after priming or disease induction is more clinically relevant, but the trials have been less successful. Using therapeutic feeding of peptides to inhibit experimental autoimmune uveoretinitis (EAU) induced in LEW rats by bovine S-Ag peptides, we found that only mild disease could be inhibited if feeding was delayed until after immunization, and relatively high feeding doses were required. In recipients with more severe EAU, the clinical efficacy of therapeutic feeding was minimal despite concurrent down-regulation of in vitro antigen-specific lymphocyte proliferation and serum antibody responses. No further inhibition of EAU was found by increasing the feeding dose. Feeding the same peptides prior to immunization produced resistance to moderate to severe disease induction. Unlike prophylactic feeding protocols, conditions were found such that feeding after immunization with low doses of antigen led to worsening of mild disease, raising a note of caution.

Human antiretinal antibodies in toxoplasma retinochoroiditis

BACKGROUND/AIMS

Toxoplasma retinochoroiditis (TR) is an important cause of blindness and visual morbidity, affecting young adults. It has been postulated that some of the retinal damage observed in TR is due to antiretinal autoimmune mechanisms.

METHODS

Humoral antiretinal autoimmunity in TR was investigated by indirect immunofluorescence (IIF) on normal human cadaveric retina and by a human retinal S-antigen ELISA. 36 patients with TR were separated on clinical grounds into those with first recurrence of disease (n = 18) or those with multiple recurrences (n = 18). Patients were also segregated into those with active (n = 28) or quiescent disease (n = 8). Serum from 16 normal controls (six with positive toxoplasma serology and 10 without) with no evidence of eye disease and 12 patients with idiopathic retinal vasculitis (IRV) were also tested.

RESULTS

Sera from 34 of the 36 patients (94%) with TR demonstrated photoreceptor layer reactivity by IIF contrasting with six of 16 normal controls (p = < 0.001) and three of 12 IRV patients (p = < 0.001). Titres of antiphotoreceptor antibody were also higher among TR patients than controls. Sera from 27 of the 36 TR patients, 10 of 16 normals, and nine of 12 retinal vasculitis patients possessed anti-human retinal S-antigen antibodies at a titre of 1:400 or more as assessed by ELISA (p = > 0.05). Antiretinal autoantibody as detected by IIF did not run in parallel with S-antigen reactivity.

CONCLUSIONS

The data indicate that the extent of antiretinal reactivity within TR is not accounted for by anti-S-antigen antibodies alone. This remarkably high prevalence of antiphotoreceptor antibody in TR as opposed to that found in either healthy or disease controls suggest that these antibodies may be co-pathogenic in toxoplasma retinochoroiditis.

Increased vascular endothelial growth factor (VEGF) and transforming growth factor beta (TGFbeta) in experimental autoimmune uveoretinitis: upregulation of VEGF without neovascularization

Experimental autoimmune uveoretinitis (EAU) was induced in Lewis rats and B10.A mice by immunization with S-antigen (S-Ag) to study the potential roles of vascular endothelial growth factor (VEGF) and the beta1 and beta2 isoforms of transforming growth factor (TGFbeta1 and TGFbeta2) during the progression of the disease. VEGF has been implicated as an angiogenic factor in ischemic retinopathies; however, Lewis rats developing EAU have high levels of VEGF in the retina, but no neovascularization. In the present study, immunohistochemical staining for VEGF, TGFbeta1 and TGFbeta2 was performed on the retinas of Lewis rats developing EAU or with oxygen-induced ischemic retinopathy. In rats immunized with S-antigen, a marked upregulation of VEGF was immunohistochemically visualized from the inner nuclear layer to the inner limiting membrane prior to blood-retinal barrier (BRB) failure and lymphocytic infiltration. VEGF is normally induced by hypoxia and its induction leads to neovascularization. Coincident with the increase in VEGF, there was increased immunoreactivity for TGFbeta1 and TGFbeta2 within the same layers of the retina. In contrast, rats with ischemic retinopathy and retinal neovascularization showed only a modest increase in VEGF immunoreactivity, which is largely confined to retinal ganglion cells and inner retinal vessels, and little or no increase in TGFbeta1 or TGFbeta2. In addition, in mice developing EAU, which does not have an abrupt onset as it does in rats and may involve neovascularization, a comparable upregulation of VEGF in the inner retina to that seen in rats developing EAU occurs with no increase in TGFbeta1 or TGFbeta2. Since TGFbeta can inhibit endothelial cell proliferation, it is likely that an increase in TGFbeta may prevent VEGF from exerting its endothelial growth activity in the rat EAU model, but VEGF may be operative in inducing BRB failure. These data suggest that there is a complex interaction among growth factors in the retina and that retinal neovascularization may require an imbalance between stimulatory and inhibitory factors.

IL-10 has a protective role in experimental autoimmune uveoretinitis

The role of IL-10 in the regulation of ocular autoimmune disease was studied in experimental autoimmune uveoretinitis (EAU) elicited in mice by immunization with the retinal antigen interphotoreceptor retinoid binding protein. IL-10-deficient mice were susceptible to EAU, indicating that pathogenesis can occur without presence of IL-10. Treatment of normal mice with IL-10 for 5 days after uveitogenic immunization ameliorated subsequent EAU scores, and down-regulated antigen-specific production of tumor necrosis factor-alpha and IFN-gamma. A concomitant treatment with IL-4 further reduced disease, and resulted in emergence of antigen-specific IL-4 and IL-10 production, as well as in enhancement of the IgG1 antibody isotype. IL-4 by itself was not protective. Only IL-10, but not IL-4, was able to inhibit the function of differentiated uveitogenic T cells in culture. Expression of mRNA for Th1 and Th2 cytokines in the eye during the course of EAU showed that while a Th1 pattern predominated early, IL-10 mRNA expression coincided with down-regulation of the Th1 response and resolution of EAU. Systemic neutralization of IL-10 during the expression phase of EAU resulted in elevated disease scores. Our results suggest that endogenous IL-10 limits expression of EAU and may play a role in the natural resolution of disease. The data further suggest that exogenous IL-10 may be useful in therapeutic control of autoimmune uveitis. While IL-10 by itself is sufficient to suppress Th1 effector development and function, a concomitant administration of IL-4 is required to shift the autoimmune response towards a non-pathogenic Th2 pathway.