Experimental autoimmune anterior uveitis (EAAU). II. Dose-dependent induction and adoptive transfer using a melanin-bound antigen of the retinal pigment epithelium

Experimental autoimmune uveitis and other animal models of uveitis: An update

Over the past several decades, animal models of autoimmune uveitis directed at eye-specific antigens (Ags) have been developed. These have allowed researchers to understand the basic mechanisms that lead to these diseases and also recently helped the researchers in translational research for therapeutic interventions. Experimental autoimmune uveitis (EAU) is an animal disease model of human endogenous uveitis and can be induced in susceptible animals by immunization with retinal Ags. Ever since the first description of EAU in mice in 1988, several animal models of uveitis has been described by researchers. Disease-specific model for cytomegalovirus retinitis and tubercular uveitis has evolved our understanding of these complex entities. Endotoxin induced uveitis is another useful model for anterior uveitis, which is not an autoimmune process and is triggered by injection of bacterial endotoxin (lipopolysaccharides) resulting in a rapid short lasting uveitis. The current article will give an insight into the various EAU animal models and their current implications in translational research. The article will also highlight the different grading systems for EAU in the animal model.

Expression of MicroRNAs in the Eyes of Lewis Rats with Experimental Autoimmune Anterior Uveitis

Purpose. This study aimed to determine the dynamic changes of NF-κB-related microRNAs (miRNAs) and cytokines over the course of experimental autoimmune anterior uveitis (EAAU) and elucidate the possible immunopathogenesis. Materials and Methods. Uveitis was induced in Lewis rats using bovine melanin-associated antigen. The inflammatory activity of the anterior chamber was clinically scored, and leukocytes in the aqueous humor were quantified. RNA was extracted from the iris/ciliary bodies and popliteal lymph nodes to reveal the dynamic changes of eight target miRNAs (miR-155-5p, miR-146a-5p, miR-182-5p, miR-183-5p, miR-147b, miR-21-5p, miR-9-3p, and miR-223-3p) and six cytokine mRNAs (IFN-γ, IL-17, IL-12A, IL-1β, IL-6, and IL-10). In situ hybridization of miRNA and enzyme-linked immunosorbent assay quantification of cytokines were performed to confirm the results. Results. Disease activity and leukocyte quantification were maximum at day 15 after immunization. The profiling of miRNA revealed downregulation of miR-146a-5p, miR-155-5p, miR-223-3p, and miR-147b and upregulation of miR-182-5p, miR-183-5p, and miR-9-3p. Cytokine analysis revealed IFN-γ, IL-17, IL-12A, IL-1β, and IL-6 overexpression, with IL-10 downregulation. Conclusions. Dynamic changes of miRNAs were observed over the course of EAAU. By initiating NF-κB signaling, the expressions of downstream cytokines and effector cells from the Th17 and Th1 lineages were sequentially activated, contributing to the disease.

Chitosan oligosaccharides attenuate ocular inflammation in rats with experimental autoimmune anterior uveitis

We investigated the protective effects and mechanisms of chitosan oligosaccharides (COS) on experimental autoimmune anterior uveitis (EAAU) in rats. EAAU was induced in Lewis rats by footpad and intraperitoneal injections of melanin-associated antigen. The rats received intraperitoneal injections of low-dose (5 mg/kg) or high-dose (10 mg/kg) COS or PBS daily after the immunization. The effects of COS were evaluated by determining the clinical scores and the morphology of the iris/ciliary body (ICB). The expression of inflammatory mediators was evaluated using western blot, immunofluorescence, and ELISA. Treatment with COS significantly attenuated the clinical scores and the leukocyte infiltration in the ICB in a dose-dependent manner. COS effectively reduced the expression of inflammatory mediators (TNF-α, iNOS, MCP-1, RANTES, fractalkine, and ICAM-1). Moreover, COS decreased the IκB degradation and p65 presence in the ICB, which resulted in the inhibition of NF-κB/DNA binding activity. In an in vitro study, sensitized spleen-derived lymphocytes of the COS-treated group showed less chemotaxis toward their aqueous humor and decreased secretion of the above inflammatory mediators in the culture media. COS treated EAAU by inhibiting the activation of NF-κB and reducing the expression of inflammatory mediators. COS might be a potential treatment for acute anterior uveitis.

Immunotherapeutic strategies in autoimmune uveitis

Autoimmune uveitis is an organ-specific disorder characterized by irreversible lesions to the eye that predominantly affect people in their most productive years and is among the leading causes of visual deficit and blindness. Currently available therapies are effective in the treatment of a wide spectrum of uveitis, but are often associated with severe side effects. Here, we review ongoing research with promising immunomodulatory therapeutic strategies, describing their specific features, interactions and the responses triggered by the targeted immune molecules that aim to minimize clinical complications and the likelihood of disease relapse. We first review the main features of the disease, diagnostic tools, and traditional forms of therapy, as well as the animal models predominantly used to understand the pathogenesis and test the novel intervention approaches aiming to control the acute immune and inflammatory responses and to dampen chronic responses. Both exploratory research and clinical trials have targeted either the blockade of effector pathways or of their companion co-stimulatory molecules. Examples of targets are T cell receptors (CD3), their co-stimulatory receptors (CD28, CTLA-4) and corresponding ligands (B7-1 and B7-2, also known as CD80 and CD86), and cytokines like IL-2 and their receptors. Here, we summarize the available evidence on effectiveness of these treatments in human and experimental uveitis and highlight a novel CD28 antagonist monovalent Fab′ antibody, FR104, which has shown preclinical efficacy suppressing effector T cells while enhancing regulatory T cell function and immune tolerance in a humanized graft-versus-host disease (GVHD) mice model and is currently being tested in a mouse autoimmune uveitis model with encouraging results.

Biologic agents in experimental autoimmune uveitis

Experimental uveitis models were developed in an effort to elucidate the pathogenesis of human uveitis. The therapeutic effects of numerous anti-inflammatory agents including corticosteroids and immunomodulatory agents including biologic response modifiers have been investigated in both experimental and human uveitis. Monoclonal antibodies to tumor necrosis factor alpha and anti-interleukins, among others, demonstrate efficacy and are employed in the treatment of uveitis refractory to conventional immunomodulatory agents.

Elevated levels of anti-endotoxin antibodies in patients with bilateral idiopathic acute anterior uveitis

PURPOSE

Endotoxins have been proved to be responsible for acute anterior uveitis (AAU) in animals in a well-established experimental model of endotoxin-induced uveitis (EIU). The purpose of our study was the detection of antibodies against endotoxins of selected enterobacteria in the serum of patients with idiopathic AAU and searching for correlations between the levels of these antibodies and the presence of HLA-B27 antigen as well as characteristic signs of EIU such as bilaterality and the absence of spontaneous recurrences of the disease.

METHODS

Reactions of serum IgG antibodies with lipopolysaccharides (LPSs) of Escherichia coli O1, E. coli O10, E. coli O111, E. coli J5, and Klebsiella pneumoniae O3 were determined for 60 patients with idiopathic AAU and 40 healthy volunteers. The presence of HLA-B27 antigen in patients was determined. Documentation of the frequency of recurrences of AAU during a follow-up period of 8 years was collected.

RESULTS

We have observed that the sera of patients with a first attack of AAU reacted stronger with the LPS of K. pneumoniae O3 than the sera of patients with relapse of the disease. Patients with bilateral AAU had markedly higher levels of antibodies against four of the five used LPSs than patients with one eye involved. A multiply comparison showed higher levels of IgG reacting with LPS of E. coli O111 in patients with bilateral eye inflammation admitted with the first attack of AAU comparing to controls. The incidence of recurrent form of AAU was significantly increased in HLA-B27-positive patients compared to HLA-B27-negative patients. However, we found in HLA-B27 carriers that those with the bilateral form of AAU had over three times smaller risk of recurrence and showed stronger immunization by endotoxins than patients with unilateral inflammation.

CONCLUSION

Our results suggest a potential role of endotoxins in the aetiology of the nonrecurrent bilateral form of AAU. We suggest that not only HLA-B27 status but also determination of number of involved eyes may be useful to assess the risk of recurrence of the idiopathic AAU.

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 Experimental Autoimmune Anterior Uveitis by Adenovirus-Mediated Transfer of the Interleukin-10 Gene

AIMS

The aim of this study was to investigate the efficiency of adenoviral-mediated transfer of the interleukin (IL)-10 gene for inhibition of experimental autoimmune anterior uveitis, a rat model of human acute anterior uveitis. Uveitis was induced in the Lewis rat by simultaneous injection of melanin-associated antigen intraperitoneally (i.p.) and into the left footpad. The animals were treated by systemic administration of adenoviral construct expressing IL-10 (Ad-IL-10) or Ad-Mock carrying no cytokine transgene.

RESULTS

A significant reduction in ocular inflammation was noted for rats that received one or two divided i.p. administrations of Ad-IL-10 (one 10 x 10(9) and two 5 x 10(9) particles of adenoviral construct, respectively), as judged by reduced clinical scores and decreased leukocyte infiltration in the anterior chamber and confirmed by histological examinations, relative to control animals. Systemic Ad-IL-10, treatment also revealed a higher serum level of IL-10, compared to the controls.

CONCLUSIONS

The results suggest that systemic adenovirus-mediated IL-10 gene therapy has an anti-inflammatory effect on immune-mediated ocular inflammation and that this approach may be promising for the treatment of acute anterior uveitis.

Acute anterior uveitis and HLA-B27

Acute anterior uveitis is the most common form of uveitis. HLA-B27-associated acute anterior uveitis is a distinct clinical entity that has wide-ranging medical significance due to its ocular, systemic, immunologic, and genetic features. The association between HLA-B27 and the spectrum of HLA-B27-associated inflammatory diseases remains one of the strongest HLA-disease associations known to date. This review examines acute anterior uveitis with particular focus on HLA-B27-associated acute anterior uveitis, including the epidemiology, immunopathology, association with HLA-B27 and its subtypes, clinical features, complications, prognosis, and potential new therapies such as anti-TNFalpha therapy and oral HLA-B27-peptide tolerance. There have been substantial recent advances in both clinical and basic scientific research in this field, including studies of the various animal models of acute anterior uveitis and the HLA-B27 transgenic animals, and these are summarized in this review. To the ophthalmologist, HLA-B27-associated acute anterior uveitis is an important clinical entity that is common, afflicts relatively young patients in their most productive years, and is associated with significant ocular morbidity due to its typically recurrent attacks of inflammation and its potentially vision-threatening ocular complications. Furthermore, to the ophthalmologist and the internist, HLA-B27-associated acute anterior uveitis is also of systemic importance due to its significant association with extraocular inflammatory diseases.

Effects of pyrrolidine dithiocarbamate, an NF-kappaB inhibitor, on cytokine expression and ocular inflammation in experimental autoimmune anterior uveitis

AIMS

The aim of this study was to investigate the effects of pyrrolidine dithiocarbamate (PDTC), a nuclear factor (NF)-kappaB inhibitor, on cytokine expression and suppression of anterior chamber inflammation in experimental autoimmune anterior uveitis. Uveitis was induced in the Lewis rats with the injection of a melanin-associated antigen into the peritoneum and footpad. At defined time points, cytokine mRNA expressions in the iris and ciliary body were measured by using a semiquantitative polymerase chain-reaction method.

RESULTS

We found that interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF)-alpha mRNA expression peaked during the active phase of uveitis, whereas interleukin (IL)-10 mRNA increased during the disease resolution. In a separate experiment, PDTC (100 and 200 mg/kg/day) was administrated intraperitoneally daily after immunization. We found that PDTC (100 and 200 mg/kg/day) effectively suppressed ocular inflammation, as indicated by reduced clinical scores and inflammatory cells infiltration in aqueous humor and the iris and ciliary body.

CONCLUSIONS

The inhibitory effects of PDTC are mainly resulted from inhibiting the expression of proinflammatory cytokines, TNF-alpha and IFN-gamma but augmenting anti-inflammatory cytokines, IL-10 expression. These findings suggest that the application of NF-kappaB inhibitors may be a potential therapeutic method for the treatment of acute anterior uveitis.

Characterization of rat CD8+ uveitogenic T cells specific for interphotoreceptor retinal-binding protein 1177-1191

The uveitogenic T cells that mediate experimental autoimmune uveitis are commonly assumed to be exclusively CD4(+). In the present study, we showed that, although a panel of long-term cultured rat uveitogenic T cell lines specific for the interphotoreceptor retinal-binding protein peptide, R16, all expressed CD4, approximately 40% of the R16-specific uveitogenic T cells freshly prepared from Ag-immunized rats were CD8(+)alphabetaTCR(+), as demonstrated by CFSE staining. We showed that the expansion of these CD8(+)alphabetaTCR(+) T cells was Ag-specific and that highly purified CD8(+) R16-specific T cells were able to induce uveitis on transfusion into naive rats. Moreover, CD8(+) uveitogenic T cells more readily switched phenotype from, and to, TCR(-)CD8(-)CD4(-) during in vivo or in vitro activation compared with their CD4(+) counterparts. In a previous study, we showed that highly purified CD8(+) myelin oligodendrocyte glycoprotein-specific T cells induced more severe autoimmune encephalomyelitis than the corresponding CD4(+) T cells. In this study, we show that an interphotoreceptor retinal-binding protein peptide consistently activated a high proportion of CD8(+)alphabetaTCR(+) T cells, which were uveitogenic in Lewis rats.

Expression of chemokine and receptors in Lewis rats with experimental autoimmune anterior uveitis

The purpose of this study is to investigate the sequential expression of certain chemokines and chemokine receptors in the iris-ciliary body and popliteal lymph nodes of Lewis rats and, thus, to establish their roles in experimental autoimmune anterior uveitis. Uveitis was induced with the injection of melanin-associated antigen intraperitoneally and into the left foot. The clinical severity of the uveitis was scored. At defined time points, CC chemokines (monocyte chemoattractant protein-1, macrophage inflammatory protein-1, and regulated-upon-activation normal T-cell expressed and secreted), CXC chemokines (interferon gamma-inducible protein-10, stromal-derived factor-1, and interleukin-8), and receptor (CCR2, CCR3, CCR5, CXCR1, CXCR2, CXCR3, and CXCR4) mRNA expression were semiquantified by using a reverse-transcriptase reaction followed by polymerase chain reaction. The concentrations of macrophage inflammatory protein-1 and regulated-upon-activation normal T-cell expressed and secreted in aqueous humor were determined by means of enzyme-linked immunosorbent assay. Levels of monocyte chemoattractant protein-1, macrophage inflammatory protein-1 and interferon gamma-inducible protein-10 started increasing before the clinical onset of disease; these might have been involved in the initial recruitment of inflammatory cells. The level of regulated-upon-activation normal T-cell mRNA, however, started rising concurrently with the onset of clinical disease, suggesting that this chemokine may exert amplifying role in generating uveitis. Stromal-derived factor-1 exhibited an early and high level of expression with the increase of cognate receptor, CXCR4, indicating that stromal-derived factor-1 plays a role in either promoting angiogenesis or attracting for T-cells. Instead of upregulation like other chemokine receptors, interleukin-8 receptors, CXCR1and CXCR2, mRNA could not be detected in accord with the increase of interleukin-8. These findings appeared that downregulation of chemokine receptors on neutrophils may make themselves less respond to interleukin-8 and subsequently lead to decreased recruitment of neutrophils into the iris-ciliary body. In addition, the expression of chemokine receptors in popliteal lymph nodes were earlier than those in the iris-ciliary body. This sequence of expression may reflect the process of T lymphocytes maturation and differentiation. Monocyte chemoattractant protein-1 protein was immunohistologically detected in the ciliary epithelium and infiltrating leukocytes. The above results suggest that chemokines, which act on T cells and monocytes, are sequentially upregulated during the clinical course of experimental autoimmune anterior uveitis, and thus, may contribute to the pathogenesis of acute anterior uveitis.

Conversion of Monophasic to Recurrent Autoimmune Disease by Autoreactive T Cell Subsets

Autoimmune uveitis has been elicited in susceptible rodents by several ocular-specific Ags. In most of these animal models the induced uveitis is acute and monophasic. Because recurrent uveitis poses the highest risk for blinding ocular complications in human disease, a spontaneous relapsing animal model would be most helpful in understanding the disease pathogenesis. In our current study we have observed that the adoptive transfer of interphotoreceptor retinoid-binding protein residues 1177-1191-specific T cells to naive Lewis rats induced a chronic relapsing disease, in contrast to the monophasic disease induced by immunization with interphotoreceptor retinoid-binding protein residues 1177-1191 emulsified in CFA. The chronic relapsing uveitis induced by autoreactive T cell subsets is dependent on the number of autoreactive T cells generated as well as their activation status. Our study documented a spontaneous model of recurrent uveitis in the rat, which should assist us in the study of disease pathogenesis and the design of specific therapy.

Activation of the alternative complement pathway by fungal melanins

Melanins are complex biological pigments formed by the oxidative polymerization of phenolic and/or indolic compounds. These pigments have been implicated in the pathogenesis of some microbial infections, malignancies, degenerative disorders, and autoimmune diseases. Recent studies have demonstrated that melanins have antigenic and anti-inflammatory properties. These findings led us to further explore the interaction of melanins with the immune system. Melanin particles ("ghosts") were isolated from in vitro-melanized Cryptococcus neoformans cells and Aspergillus niger conidia and then incubated in normal human serum containing (125)I-labeled complement C3. The results demonstrated deposition of C3 fragments onto the melanin ghosts as early as 1 min after incubation, with maximum deposition occurring after 12 min for C. neoformans-derived melanin ghosts and after 25 min for A. niger-derived melanin ghosts. The blocking of classical pathway activation did not affect the kinetics or total deposition of C3 onto the melanin ghosts, indicating that melanins activate complement through the alternative pathway. Immunofluorescence analysis of lungs from BALB/c mice injected intratracheally with C. neoformans-derived melanin ghosts demonstrated deposition of C3 fragments onto the ghosts. Small granulomas were also observed surrounding the ghosts. However, melanization of the C. neoformans cell wall did not alter the kinetics or total deposition of C3 fragments onto the fungal cells. The finding that melanin surfaces can activate the complement system suggests a potential mechanism for the pathogenesis of some degenerative and/or autoimmune processes that involve melanized cells as well as another potential role for melanin in the virulence of melanin-producing microorganisms.

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.

Inhibition of experimental melanin protein-induced uveitis (EMIU) by targeting nitric oxide via phosphatidylcholine-specific phospholipase C

Experimental melanin protein-induced uveitis (EMIU) is an autoimmune uveitis induced by immunization with uveal melanin protein. Fas and FasL enhancement is reported in rats with EMIU. Tricyclodecan-9-yl-xanthogenate (D609), a specific inhibitor of phosphatidylcholine-specific phospholipase C, inhibits inducible nitric oxide synthase (iNOS) induction. In two independent experiments, 35 Lewis rats with EMIU received either D609 or PBS daily. The eyes and draining lymph nodes were collected for histology, analyses of nitrite, peroxide, and superoxide dismutase, Fas and FasL immunochemistry, in situ hybridization for iNOS mRNA and in situ apoptosis detection at the peak of the disease. Both experiments showed significant inhibition of EMIU by D609. Decreases in nitrite and peroxide, increase of superoxide dismutase and lower expressions of iNOS mRNA were found in D609-treated, as compared to PBS-treated eyes. There was mild enhancement of Fas and FasL in the eyes and lymph nodes of D609-injected animals. DNA fragmentation was increased in the lymph nodes of D609-treated rats. We conclude that iNOS activation is responsible for NO production in eyes with EMIU. The suppressive effect of D609 on EMIU may result from scavenging NO and activating apoptosis previously inhibited by NO along with other anti-inflammatory effects.

Experimental melanin-induced uveitis in the Fischer 344 rat is inhibited by anti-CD4 monoclonal antibody, but not by mannose-6-phosphate

Experimental melanin-induced uveitis (EMIU) is a rodent model of acute anterior uveitis which was described in 1993. We investigated strain susceptibility, and age and gender characteristics of the model, undertook histological and immunohistochemical studies to investigate underlying cellular mechanisms, and examined several treatment options. Rats were immunized with bovine ocular melanin (250 microg), and disease was followed by slit lamp examination. Lewis, Fischer 344 and Porton rats were found to be susceptible to EMIU, whereas Wistar-Furth, DA, and Hooded Wistar strains were resistant. EMIU was neither age- nor gender-dependent. In Fischer 344 rats, EMIU was characterized clinically by florid anterior segment inflammation. Histopathological findings included infiltration of ciliary body and iris with mononuclear cells and neutrophils. Both CD4+ and CD8+ T lymphocytes were prominent. Rats were then treated with intraperitoneal injections of anti-CD4, anti-CD8 or irrelevant isotype-matched MoAb on days -3, 0, 3, 6 and 9 with respect to melanin immunization. Incidence of uveitis was significantly reduced in rats treated with a non-depleting cocktail of anti-CD4 MoAbs (P = 0.007), whereas a depleting anti-CD8 antibody had no effect on the disease. Mannose-6-phosphate inhibits lymphocyte migration in some models of T cell-mediated inflammation. This simple sugar was administered to additional rats via intraperitoneal osmotic pumps for 14 days following disease induction, but did not influence the uveitis. We conclude that EMIU is controlled by CD4+ T cells, and disease may be abrogated by treatment with anti-CD4 MoAbs.

Basic pathogenic mechanisms operating in experimental models of acute anterior uveitis

Acute anterior uveitis is a recurrent inflammatory disease of the eye that occurs commonly, is distressing for the patient, and may have potentially blinding sequelae. The pathogenesis of the disease is poorly understood, and anti-inflammatory treatment is consequently non-specific and may be associated with significant complications. Animal models are a possible key to a better understanding of this disease. In one model, rats and mice develop a relatively short-lived anterior uveal inflammation almost immediately after systemic injection of bacterial endotoxin. Accumulating evidence suggests that cytokine production by resident uveal macrophages initiates endotoxin-induced uveitis which is characterized by an infiltration of neutrophils and mononuclear cells. A second model displays features in keeping with a delayed-type hypersensitivity immune response. Experimental melanin-induced uveitis is an acute recurrent uveitis with delayed onset but extended duration, observed when rats are immunized with bovine ocular melanin. Both animal models have clinical features in common with acute anterior uveitis, although experimental melanin-induced uveitis appears to mimic the human disease more closely. Novel treatment options to target implicated inflammatory cells and molecules are currently under consideration.

The Antibody Response to Fungal Melanin in Mice

Melanins are associated with virulence in several important human pathogens, but little is known about the immune response to this ubiquitous biologic compound. We hypothesized that melanin produced by the fungus Cryptococcus neoformans was immunogenic. C. neoformans melanin was purified from melanized fungal cells and was used to immunize C57BL/6, BALB/c, and T cell-deficient (nude) BALB/c mice. The Ab response was evaluated by ELISA, immunofluorescence, and agglutination. The results demonstrate that melanin can be immunogenic, and the humoral immune response is T cell independent. Furthermore, the experiments demonstrate 1) a sensitive ELISA for the measurement of Ab to melanin, 2) that mice mount an intense Ab response to fungal melanin that includes Abs of IgM and IgG isotypes, 3) that melanins from different sources have cross-reactive epitopes, and 4) melanin in the cell wall of melanized yeast cells reacts with Abs raised to l-dopa C. neoformans melanin. The biologic significance of Ab to melanin remains to be determined, but the development of Ab suggests that this amorphous insoluble polymer can stimulate the immune system. The serologic techniques described here may prove useful for the evaluation of Ab responses to melanin in a variety of diseases.

Uveitogenic proteins isolated from bovine iris and ciliary body

Experimental autoimmune anterior uveitis (EAAU) is an animal model for acute anterior uveitis in humans. Previously, we have shown that EAAU can be induced in Lewis rats by a protein(s) associated with ocular melanin. The present study was designed to further purify the pathogenic antigen. Melanin associated antigen (MAA), isolated from bovine iris and ciliary body, was digested with V8 protease and the soluble protein separated on a cation exchange column. The bound protein was eluted with a salt gradient. Lewis rats were immunised with the resulting fractions to test for pathogenicity. Moderate to severe EAAU, with clinical and histopathological features similar to induction with crude soluble bovine MAA, was observed with the 100-200 mM gradient of NH4Cl. Thus, bovine MAA has been partially purified using cation exchange chromatography. Studies are currently under way to purify bovine MAA to homogeneity.

Differential effect of macrophage depletion on two forms of experimental uveitis evoked by pigment epithelial membrane protein (EAPU), and by melanin-protein (EMIU)

The purpose of the present study was to clinically and histologically investigate the influence of macrophage depletion on the development of experimental autoimmune pigment epithelial membrane protein-induced uveitis (EAPU), and experimental melanin-protein induced uveitis (EMIU) in the Lewis rat. EAPU is mainly characterized by pigment epitheliitis. Posterior mononuclear cell accumulations enclose and destroy the retinal pigment epithelium (RPE). In EMIU the inflammation is specifically localized in the uvea. EAPU was induced by immunization with RPE membrane protein, and EMIU was evoked by immunization with purified choroidal melanin. Systemic treatment with dichloromethylene diphosphonate (Cl2MDP)-containing liposomes just before the expected beginning of the clinical signs of EAPU (at day 7 and 9 after immunization) resulted in a considerable delay of the uveitis process. In the treated animals the typical plaque shaped cell accumulations (containing many macrophages) along the RPE were lacking. Two weeks after the treatment, severe rebound EAPU developed. Local treatment by subconjunctival liposome injections did not exert any effect on EAPU. In EMIU, macrophage depletion by systemic treatment did not noticeably influence the clinical and histological development of the inflammation. Systemic treatment at the peak stage of EAPU (at day 12 and 14 after immunization) resulted in the rapid disappearance of the clinical signs of uveitis. Vitreous and anterior chamber cells were virtually absent two days later. This situation remained unchanged until the experiment was terminated two weeks later. Already deposited cell accumulations along the RPE did not regress but stopped their progression. Hematogenous macrophages thus appear to play a crucial role in the development of EAPU but the effect of early macrophage depletion on EAPU appeared to be temporary due to blood repopulation. A possible explanation for the differential influence of macrophage depletion on EAPU and EMIU is discussed, and is based on differences in immunopathogenesis.

Resident and infiltrating cells in the rat iris during the early stages of experimental melanin protein-induced uveitis (EMIU)

Experimental melanin protein-induced uveitis (EMIU) is reported to be a model of anterior uveitis and choroiditis in which the retina is spared. In this study, we chose to compare EMIU with experimental autoimmune uveoretinitis (EAU), a well-recognised model of endogenous posterior uveitis, with regard to the nature and dynamics of the cellular infiltrate in the iris. Female Lewis albino rats were immunised with mixtures of crude retinal extract/complete Freund's adjuvant (CFA) (EAU), phosphate-buffered saline/CFA (controls), or iris melanin/CFA (EMIU) using established protocols. Animals were sacrificed on days 10 and 13 (around disease onset). Following whole body perfusion fixation, irides were dissected from the remainder of the globe. Iris wholemount preparations were then subjected to immunohistochemical analysis in order to investigate both the dynamics of infiltrating leukocytes and the effects of the inflammatory changes on resident immune cells in the iris. The nature of the cellular infiltrate in both EMIU and EAU models was essentially similar, namely there was a rich infiltrate of EDI+ mononuclear cells, Ox42+ neutrophils and T cells. Resident tissue macrophages (ED2+) were slightly below normal densities in the iris of EAU animals and marginally elevated in EMIU animals, MHC class II (Ia) staining, associated in the normal eye with dendritic cells (DC), was considerably elevated in EMIU. It is likely that this was due to both increased DC numbers and an influx of Ia+ exudate macrophages. No striking difference was found in the nature and phenotype of the cellular infiltrate in the iris at the onset of the disease in these two models of uveitis (EAU and EMIU). This suggests that the anterior segment inflammation in both models represents non-specific changes secondary to cytokine release associated with interaction of activated antigen-specific T cells and target antigens, namely retinal photoreceptors in EAU and uveal tract melanin-containing cells in EMIU. Alternatively, it may suggest that antigen-presenting cells resident in the iris and ciliary body in normal eyes have access to ocular antigens on both sides of the blood-ocular barrier and are capable of activating circulating antigen-specific T cells in these models.

Uveitogenic 28/30 kD and 43 kD polypeptides in pigment epithelial membranes of the retina

The purpose of this study was the search for new intrinsic polypeptides of the retinal pigment epithelium (RPE) capable of evoking experimental uveitis. A membrane fraction was prepared from purified bovine RPE cells. The Triton X-100 soluble protein fraction was separated into polypeptide fractions by preparative gel electrophoresis, and the pathogenicity of the main isolated polypeptides was investigated in Lewis rats. After immunization, two hitherto unknown pigment epithelial polypeptides with M(r) 28/30 kD (doublet) and 43 kD (PEP-28/30 and PEP-43, respectively) elicited progressive pigment epitheliitis and choroiditis accompanied by extending plaque-shaped macrophage accumulations along the RPE-Bruch's membrane layer. No inflammatory foci were found within the neural retina. Polypeptide fractions with M(r) 14-17, 25 and 32/34 kD (doublet) (PEP-14/17, PEP-25 and PEP-32/34, respectively) appeared to be non-uveitogenic at the tested dose. PEP-28/30 and PEP-43 exhibited a partial antigenic relationship to PEP-65. PEP-28/30 exhibited marked reactivity to a monoclonal antibody previously raised to a 32 kD RPE-specific protein.

IN CONCLUSION

in addition to the previously described main RPE-specific membrane polypeptide PEP-65, the RPE appears to contain two more uveitogenic components, the intrinsic pigment epithelial membrane polypeptides PEP-28/30 and PEP-43. Like PEP-65, these antigens are able to evoke experimental autoimmune pigment epithelial protein-induced uveitis (EAPU) in rats.

Immunohistochemical studies on melanin associated antigen (MAA) induced experimental autoimmune anterior uveitis (EAAU)

Experimental autoimmune anterior uveitis (EAAU), a model of uveitis induced by sensitization to melanin associated antigen (MAA) derived from the iris and ciliary body, closely resembles human acute anterior uveitis. The immunopathogenesis of EAAU was studied by immunohistochemical detection of immune cells and the expression of Ia, ICAM-1 and LFA-1 antigens. Male Lewis rats were immunized with bovine MAA, mixed with CFA and pertussis toxin in the hind foot pad. Animals were examined daily by slit-lamp biomicroscopy and serially sacrificed up to 30 days. Immunohistology of the enucleated eyes was performed with monoclonal antibodies W3/25 (CD4), OX-8 (CD8), ED2 (macrophage), OX-33 (B cell), OX-6 (Ia), IA29 (ICAM-1) and WT.1 (LFA-1). During each stage of EAAU, CD4+ T cells predominated over both CD8+ T cells and macrophages in the uvea. Very few B cells were detected during each stage of EAAU. EAAU could not be induced by the adoptive transfer of sera obtained from immunized animals. Low levels of constitutive ICAM-1 and Ia were observed. An increase in ICAM-1 expression was first noted on the epithelial cells of the uveal tract and RPE on day 9 post immunization and preceded LFA-1 and Ia upregulation by approximately 2 days. The immunopathogenesis of EAAU appears to be linked to the presence of the CD4+ T cells.

Experimental melanin-protein-induced uveitis in the Lewis rat. Immunopathologic processes

PURPOSE

To study the immunopathology of experimental melanin-protein-induced uveitis in the Lewis rat.

METHODS

Rats were immunized with bovine ocular melanin protein. The kinetics of experimental melanin-protein-induced uveitis was studied by clinical examination and immunopathology. Cellular and humoral responses were evaluated by lymphocyte proliferation, delayed-type hypersensitivity, and agglutination. After clinical disease subsided, recurrent experimental uveitis was induced with a low-dose footpad injection of lipopolysaccharide.

RESULTS

Experimental melanin-protein-induced uveitis was characterized by bilateral uveal infiltration mainly with lymphocytes and monocytes. Delayed-type hypersensitivity, lymphocyte proliferation, and agglutination to bovine ocular melanin protein were positive. Expressions of major histocompatibility complex class II and intercellular adhesion molecule-1 were observed before ocular infiltration. The predominantly infiltrating cells were CD4+ lymphocytes. Experimental melanin-protein-induced uveitis subsided within 1 month, spontaneously recurred within 1 week in approximately one quarter of the rats, and was inducible in most rats with 5 micrograms of lipopolysaccharide confirmed by histopathology.

CONCLUSIONS

Experimental melanin-protein-induced uveitis is a T-cell-mediated autoimmune uveitis, resembling noninfectious recurrent iridocyclitis and choroiditis in humans.

Experimental autoimmune anterior uveitis (EAAU): induction by melanin antigen and suppression by various treatments

The uveitogenicity of melanin has been a controversial subject for a long time, presumably as a result of the use of ill-defined preparations in the experiments. We have developed procedures for the preparation of purified uveitogenic melanins from the retinal pigment epithelium and choroid that are free from pathogenic retinal photoreceptor proteins. The active melano-antigen is located at the surface of the melanin granules and is probably identical in both tissues. It retains its pathogenicity in hot polar detergent and during in vitro proteolysis, but it is inactivated by macrophage phagocytosis and hydrolysis in hot hydrochloric acid. Lewis rats immunized with microgram doses of bovine retinal pigment epithelial or choroidal melanin develop severe experimental autoimmune anterior uveitis (EAAU) about 10 days later. Retinitis and pinealitis are not observed. Skin melanin prepared in a similar way evokes EAAU as well, but it is only weakly pathogenic. EAAU cannot be transferred by serum, and its development can effectively be inhibited by antibodies to the inciting antigen and by cyclosporin. Vitamin E treatment of the animals causes a delay in its onset. The results indicate that cell-mediated immunity plays a dominant role in the pathogenesis of EAAU. This is the first time it has been shown that purified ocular and skin melanins are able to induce an autoimmune disease. The relevance of this finding for the study of melanin-related immunopathology in man is discussed.

Experimental autoimmune posterior uveitis accompanied by epitheloid cell accumulations (EAPU). A new type of experimental ocular disease induced by immunization with PEP-65, a pigment epithelial polypeptide preparation

Purified retinal pigment epithelial cells of bovine eyes have been fractionated by a series of buffer and detergent extractions. The electropherogram of the buffer-insoluble, Triton X-100-soluble fraction (RPE-TS) exhibits a major polypeptide band of M(r) 65 kDa and a variety of minor components. Electrophoretically purified 65 kDa-band protein (PEP-65) is immunologically unrelated to the known uveitogenic photoreceptor proteins, to other neural retina proteins, and to PEP-X, the RPE-melanin-bound uveitogenic antigen. An immunocytochemical study of eye tissues suggests that it is exclusively located in the RPE. Immunization of Lewis rats with PEP-65 or affinity-purified RPE-TS induces a new type of ocular disease: experimental autoimmune posterior uveitis accompanied by epitheloid cell accumulations (monocytes) adjacent to the RPE (EAPU). The disease starts 9 days after immunization, provided that pertussis toxin is used as co-adjuvant. The first clinical signs are transient flare and cells in the anterior chamber. Choroiditis develops, and epitheloid cells accumulate focally along one or both sides of the Bruch's membrane-RPE layer. Such foci resemble, in some respects, Dálen-Fuchs nodules which occur in human sympathetic ophthalmia. Areas of inflammation are frequently localized in the chorioretinal periphery adjacent to the pars plana. Vitreous cell infiltration is the most prominent clinical feature of EAPU. During at least 2 months, extending chorioretinal areas containing epitheloid cell collections remain while the adjacent photoreceptor cells sometimes disappear without being invaded by these cells. Retinal vasculitis is seldomly observed and pinealitis is absent. EAPU has the latter feature in common with PEP-X-induced experimental autoimmune anterior uveitis (EAAU). The two diseases differ from the various photoreceptor antigen-induced forms of EAU where pinealitis and inflammation of the neural retina are prominent features. However, just as in EAU and EAAU, EAPU can be adoptively transferred, and is inhibited by cyclosporin treatment suggesting T-cell dependency.