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.

Improved myeloperoxidase assay for quantitation of neutrophil influx in a rat model of endotoxin-induced uveitis

Previously described models of endotoxin-induced uveitis quantify neutrophil influx into the eye using biochemical or direct cell count methods that result in an underestimation of ocular leukocyte accumulation following the inflammatory stimulus. We have optimized the rat model of endotoxin-induced uveitis by first overcoming interference in the biochemical assay of myeloperoxidase due to endogenous ocular reductants and cellular constituents containing free thiol functional groups. This was accomplished by simultaneously 1) extensively diluting soluble, interfering substances and 2) blocking tissue sulfhydril functional groups during tissue homogenization. Uveitis was induced in rats by subplantar injection of endotoxin. Twenty-four hours later, eyes were enucleated, homogenized, fractionated, and myeloperoxidase activity of neutrophils sedimenting with the membranous pellet was extracted. Previously published extraction procedures yielded only 40% of total assayable myeloperoxidase activity. Optimal recovery of myeloperoxidase activity (>twofold increase) was achieved only with two sequential extractions using 50 mM phosphate buffer (pH 7.4) containing 10 mM N-ethylmaleimide, and subsequent solubilization of myeloperoxidase activity by extraction with 0.5% hexadecyltrimethylammonium bromide in 50 mM phosphate buffer (pH 6.0). This modified extraction procedure and optimized myeloperoxidase assay conditions (300 microM hydrogen peroxide and 1.5 mM o-dianisidine) were then used to enhance the uveitis model. Maximum ocular neutrophil accumulation was observed at endotoxin doses of 100-200 microg. Total ocular neutrophil infiltrations ranged from 250,000 to 800,000 cells/globe. This leukocyte influx was inhibited dose-dependently by topical ocular administration of dexamethasone, with half-maximal inhibition observed at a concentration of 0.01%, w/v. Further validated by the correlation of biochemical results with histological evaluation, the refined methodology described in this report has application in assessing the ophthalmic therapeutic potential of antiinflammatory agents.

Nitric oxide accelerates the onset and increases the severity of experimental autoimmune uveoretinitis through an IFN-gamma-dependent mechanism

The production of large amounts of nitric oxide (NO) by inducible nitric oxide synthase (iNOS) has been described as a double-edged sword eliciting pro- or anti-inflammatory effects in different immune situations. Our aim, therefore, was to investigate its role in experimental autoimmune uveoretinitis (EAU), a model of ocular inflammation, induced in the Lewis rat following a single footpad injection of retinal Ags. iNOS enzyme was not detected in the normal Lewis rat eye, but was strongly expressed by infiltrating ED1+ macrophages during the acute inflammatory stages of EAU. Treating immunized animals with L-arginine increased urinary NO metabolite (NOx) levels, accelerated the inflammatory response, and increased disease severity, whereas treatment with the NOS inhibitor, N(G)-nitro-L-arginine methyl ester, reduced NOx excretion, delayed the onset, and reduced the clinical signs of EAU. Reverse transcription-PCR analysis of ocular tissue from untreated and treated animals detected iNOS mRNA at all stages of disease, and expression was up-regulated during peak disease. L-arginine treatment enhanced cytokine mRNA expression, particularly of IFN-gamma, which was detected earlier than in control animals, corresponding with the more rapid onset of disease and increased disease severity observed in this group. N(G)-nitro-L-arginine methyl ester had little or no effect on iNOS or inflammatory cytokine mRNA expression. These results suggest NO is central to the pathogenesis of EAU and highlight the importance of the macrophage as an effector cell in what is considered a CD4+ T cell-dependent disease. Furthermore, this study demonstrates the therapeutic potential of NOS inhibitors in the treatment of inflammatory and autoimmune mediated disease.

Cellular localisation and dynamics of nitric oxide synthase expression in the rat anterior segment during endotoxin-induced uveitis

The present study examined the temporal pattern and cellular localisation of nitric oxide synthase in Endotoxin-Induced Uveitis (EIU). Lewis rats (n=40) received a single footpad injection of 200 microg of bacterial lipopolysaccharide. Animals were killed at 0, 2, 4, 6, 12, 24, 48 and 72 hr after injection and ocular tissues prepared as iris-ciliary body wholemounts or frozen sections of the anterior segment. The expression of constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) was investigated at all time points by immunohistochemistry. A further group of animals (n=6) were killed at the peak of the disease (12 hr) and the cellular co-localisation of iNOS on resident and infiltrating immune cells was investigated by double immunohistochemistry utilising the biotinylated monoclonal antibodies ED1, ED2 and Ox6. Expression of cNOS on iris vessels did not alter during the course of EIU. Quantitative analysis of iris-ciliary body wholemounts revealed the first evidence of iNOS+ at 2 hr which increased dramatically at 4 and 6 hr with a peak at 12 hr. The expression of iNOS in the early phase of the disease (2-6 hr) was associated with small round marginating and newly extravasated cells that on morphological criteria were most likely neutrophils and monocytes. At 12 hr, cells of more mixed morphologies began to express iNOS and double labelling revealed 70% of these cells were also ED1(+) (a lysosomal antigen present in monocytes/macrophages and dendritic cells), 52% were Ox6(+) (MHC class II) (dendritic cells, activated macrophages and some T-cells) and 19% were ED2(+) (pan-specific resident tissue macrophages). Expressed in an alternative manner, 10% of the total ED1(+) cell population, 11% of the ED2(+) cells and 44% of Ox6(+) cells co-expressed iNOS. Expression of iNOS decreased significantly by 24 hr to near baseline levels and was absent by 48 and 72 hr. Within the ciliary processes iNOS+ dendriform cells were noted at 6 hr and accumulations of many small round iNOS+ cells were present at 12 hr. The ciliary epithelium did not at any time express iNOS at the protein level detectable by immunohistochemistry. The results of this study suggest that iNOS expression early in EIU is associated with infiltrating or newly recruited neutrophils and monocytes/macrophages in the iris whereas later in the disease resident tissue macrophages and MHC class II+ cells (activated macrophages and putative dendritic cells) in the iris and ciliary body may synthesise nitric oxide. The role of this late phase of nitric oxide synthesis may include lymphocytostasis and immunosuppression as proposed in other tissue sites. The outcome of the present study may help in planning therapeutic strategies using NOS inhibitors.

Concomitant treatment with a 5-lipoxygenase inhibitor improves the anti-inflammatory effect of the inhibition of nitric oxide synthase during the early phase of endotoxin-induced uveitis in the rabbit

Nitric oxide (NO) synthase inhibitors, such as NG-nitro-L-arginine methyl ester (L-NAME), have been shown to attenuate endotoxin-induced uveitis (EIU) but they could increase leukocyte adhesion to the vascular endothelium. We hypothesize that a concomitant treatment with the 5-lipoxygenase inhibitor nordihydroguaiaretic acid (NDGA) in 50% dimethylsulfoxide (DMSO, a hydroxyl radical scavenger) could improve the anti-inflammatory activity of L-NAME. EIU was induced in albino rabbits by intravitreal injection of 100 ng lipopolysaccharide. Animals were treated with multiple intraperitoneal injections of 50% DMSO in phosphate-buffered saline (PBS), NDGA (10 mg/kg) in 50% DMSO, L-NAME (50 mg/ kg) in PBS, or the combination NDGA+L-NAME. Uveitis was assessed by slit lamp examination, protein levels in aqueous humor, and myeloperoxidase (MPO) activity in the iris/ciliary body 6 h after induction. Nitrite, leukotriene B4 (LTB4), prostaglandin E2 (PGE2), platelet-activating factor (PAF) and interleukin-1 beta (IL-1 beta) levels in aqueous humor were also determined. NDGA or L-NAME alone did not show a significant reduction of uveitis intensity, although a significant decrease in MPO or in proteins was found, respectively. The combination NDGA+L-NAME significantly reduced the uveitis intensity, MPO in the iris/ciliary body, and the levels of nitrites, LTB4, PGE2, and PAF in aqueous humor. IL-1 beta levels were lower than the detection limit of the radioimmunoassay in all treatment groups. We conclude that concomitant treatment with NDGA in DMSO improves the anti-inflammatory activity of L-NAME during the early phase of EIU, suggesting that the inhibition of NO synthesis could enhance leukocyte infiltration and the release of oxygen free radicals.

Expression of inducible nitric oxide synthase in the eye from endotoxin-induced uveitis rats

PURPOSE

Inducible nitric oxide (NO) synthase (iNOS) has been implicated in the pathogenesis of endotoxin-induced uveitis (EIU). This study was undertaken to localize the cells, in the eye, which express iNOS during EIU in the rat.

METHODS

EIU was induced in Lewis rats by a single foot pad injection of 150 micrograms lipopolysaccharide (LPS) from Salmonella typhimurium. At different time intervals after LPS injection, the authors evaluated ocular inflammation (slit lamp observation), iNOS localization by in situ hybridization, and comparison of OX-42- and ED1-positive cell appearance and of glial response by specific immunohistochemistry.

RESULTS

iNOS mRNA was not detected in the iris-ciliary body nor in the retina of control rats. It was detected strongly in the epithelial cells of the iris-ciliary body at 6 hours and also in stromal cells of the ciliary processes at 16 hours after LPS injection. In the neuroretina, iNOS mRNA was observed in the inner layers 16 hours after LPS injection. iNOS-positive cells were also present on the vitreous at this time. At 6 and approximately 16 hours after LPS injection, immunohistochemistry experiments revealed a large number of OX-42- and ED1-positive cells (microglia, macrophages, or polymorphonuclear leukocytes) colocalized in part with some iNOS-positive cells in the ciliary body and in the retina. Furthermore, expression of iNOS in Müller cells cannot be excluded.

CONCLUSIONS

These observations confirm that subcutaneous injection of endotoxin dramatically induces NOS mRNA expression in the eye, and they demonstrate that epithelial cells of the iris-ciliary body and cells infiltrating the anterior segment of the eye and the retina are the major source of NO. These results support the hypothesis that both inflammatory and resident ocular cells are involved in iNOS expression during EIU.

[Serum adenosine deaminase and angiotensin converting enzyme activity in patients with endogenous uveitis]

Serum activity of adenosine deaminase (ADA) and angiotensin converting enzyme (ACE) was investigated in 32 patients with sarcoidosis, 22 patients with Behçet's disease, 22 patients with Vogt-Koyanagi-Harada's (VKH) disease and 253 healthy controls. In healthy controls, the ADA level was significantly higher in females than in males (p < 0.01). In patients with sarcoidosis, the serum ADA level was significantly higher in both males and females than in the controls (p < 0.01). In patients with Behçet's disease, the serum ADA level was significantly higher than in the controls (p < 0.01) in males only. In VKH disease, the serum ADA level showed no significant difference from the normal controls. Significant elevation of the serum ACE activity was observed only in patients with sarcoidosis (p < 0.01). Serum ACE activity was therefore considered to be more specific to sarcoidosis than serum ADA activity.

Chemoattractant and neutrophil degranulation activities related to interleukin-8 in vitreous fluid in uveitis and vitreoretinal disorders

PURPOSE

To investigate whether the cytokine interleukin-8 (IL-8), a strong chemoattractant and activator for neutrophils, is responsible for neutrophil infiltration and degranulation in the eye in uveitis.

METHODS

IL-8 and elastase were measured with specific enzyme-linked immunoassays in vitreous fluid samples obtained from 69 patients with various uveitis entities. Vitreous fluid of nonuveitis patients and eye bank eyes served as controls. The chemotactic activity of vitreous fluid was tested with the Boyden chamber technique.

RESULTS

IL-8 was detected in 45% of the vitreous fluid samples from uveitis patients and in 26% of vitreous fluid samples from nonuveitis patients. Vitreous fluid samples with IL-8 levels exceeding 100 pg/ml were chemotactic for neutrophils. This chemotactic activity could be blocked by 41% to 79% with a monoclonal anti-IL-8 antibody. Elastase levels in vitreous fluid of uveitis patients with detectable IL-8 were significantly higher than those in vitreous fluid samples with no detectable IL-8.

CONCLUSION

These results indicate that IL-8 participates in the inflammatory processes in the eye by attracting and degranulating neutrophils. It is suggested that these processes contribute to the pathogenesis of tissue destruction in uveitis.

[Effect of kontrikal on the course of experimental nonspecific phacogenic uveitis]

Nonspecific phacogenic uveitis (NPGU) was simulated in 21 chinchilla rabbits to follow the time course of the blood serum proteolytic activity and the principal protease inhibitors (alpha 1 inhibitor and alpha 2 macroglobulin) in various stages of the inflammatory process. Effects of contrykal, a synthetic protease inhibitor, on these parameters and the course of the inflammation was also under study. The results evidence that i.v. and subconjunctival contrykal administration reduced the periods of NPGU treatment 1.5-2 times.

The lysosomal enzymes of the iris-ciliary body are retained in their organelles and exhibit increased activities during acute uveal inflammation

Acute uveal inflammation, characterised by conjunctival hyperaemia, limbal vascular injection, iritis and aqueous flare, was induced in the rabbit eye by a single intravitreal injection of 10 micrograms of Shigella endotoxin. Twenty-four, 48 and 72 h after endotoxin administration, lysosomal-rich fractions and cytosolic supernatants were prepared from iris-ciliary bodies and the enzymatic activities of some lysosomal hydrolases in these fractions were assayed. Acid phosphatase, aryl sulphatase and N-acetyl-B-D-glucosaminidase exhibited increased activities in the lysosomal preparations from inflamed iris-ciliary bodies, relative to the activities of the same enzymes in lysosomal fractions from normal iris-ciliary bodies. No significant differences in activities were obtained for these enzymes in cytosolic supernatants from normal and inflamed iris-ciliary bodies. The results suggest that during acute ocular inflammation the lysosomal hydrolases are retained in their organelles at an elevated state of activity.

[The kallikrein-kinin system in experimental uveitis]

The author analyzes changes in the activities of the kallikrein-kinin system (KKS) parameters over the course of experimental toxic allergic uveitis induced in 24 animals; the reference group consisted of 8 intact animals. Clinical examinations of the eyes were parallelled by biochemical analyses that revealed a significant activation of the blood serum and vitreous KKS, the degree of this activation correlating with uveitis severity. No normalization of KKS parameters was associated with complete clinical cure, this being possibly due to a chronic course of the condition and thus valuable for pathogenetically oriented therapy.

Role of free radicals in uveitis

In acute inflammation, the tissue damage is generally mediated through polymorphonuclear leukocytes and macrophages. Recent studies on the mechanism of this leukocyte-mediated cytolysis have demonstrated that these cells, on stimulation, release a variety of reactive products. These metabolic products consist of superoxide and hydrogen peroxide, which in turn can form highly reactive species such as hydroxyl radicals. It is believed that these oxygen products play an important role in the tissue damage that occurs in inflammations such as uveitis. The ocular structures contain various antioxidant enzymes that normally protect against free radical mediated injury. In experimental animal models of uveitis, it has been shown that antioxidants and free radical scavengers can function as antiinflammatory agents and can protect the eye from inflammation-mediated tissue damage.

Concentration of angiotensin-converting enzyme in tears of patients with sarcoidosis

The concentration of angiotensin-converting enzyme (ACE) was studied in 39 patients with sarcoidosis, 6 of whom had active uveitis, 7 patients with non-sarcoid uveitis and 36 healthy controls. ACE concentration in tears was also compared with total protein concentration in tears in order to exclude the effect of varying dilution of tears at sampling. Mean tear ACE concentration and ACE/protein ratio were higher in patients with sarcoidosis than in controls. There were no significant differences in tear ACE concentration or ACE/protein ratio between sarcoidosis patients with uveitis and those with no eye involvement. Tear ACE concentration and ACE/protein ratio did not correlate significantly with serum ACE concentration. It is concluded that the mean concentration of tear ACE and ACE/protein ratio are elevated in sarcoidosis, but that this elevation is independent of any eye involvement.

Angiotensin-converting enzyme in sarcoid and chalazion granulomas of the conjunctiva

Angiotensin-converting enzyme (ACE) was studied immunohistochemically in conjunctival biopsies from 6 patients with systemic sarcoidosis, 4 patients with posterior non-sarcoid uveitis and in specimens from 4 patients with chalazion of the eyelid. Specimens with sarcoid granulomas showed intense ACE-positive immunoreactivity in epitheloid cells of the granuloma, whereas chalazion granulomas did not contain ACE-immunoreactivity. There was no difference in staining patterns between specimens without granulomas. Thus immunohistochemical staining for ACE may be of help in differentiating conjunctival granulomatous tissue of a chalazion from sarcoid granuloma.

Angiotensin-converting enzyme activity in human aqueous humor

We measured aqueous angiotensin-converting enzyme (ACE) activity in 37 patients. Patients with granulomatous uveitis and probable sarcoidosis (based on increased serum ACE activity or characteristic radiologic findings) had a significant increase in aqueous ACE activity compared with normal subjects. Aqueous ACE activity was also significantly elevated in patients with sarcoid who had normal serum ACE activity. We believe that measurement of aqueous ACE activity should be considered in patients with uveitis who have normal serum ACE activity and are suspected of having sarcoidosis.

Ascorbic acid inhibits the activity of polymorphonuclear leukocytes in inflamed ocular tissues

Myeloperoxidase (MPO) is present at high levels in polymorphonuclear leukocytes (PMNs) and has been used as a marker to quantify the accumulation of PMNs in inflamed tissues. MPO activity in inflamed ocular tissues was inhibited by aspirates of aqueous humor. This inhibition could be duplicated by the addition of ascorbic acid at concentrations equivalent to those present in the aliquots of aqueous humor. Similarly, aqueous humor and ascorbic acid inhibited MPO from isolated rabbit leukocytes. Therefore, ascorbic acid appears to inhibit the functional activity of the peroxidase in PMNs, thus preventing potential tissue damage by this enzyme when released during leukocyte degranulation in inflammation. Ascorbic acid might fulfill a role as an endogenous anti-inflammatory agent in the eye.

Neutrophil collagenolytic activity in patients with Behçet disease

Studies were made on neutrophil dysfunction in Behçet disease by examining collagenolytic activity in neutrophils. The collagenolytic activity of neutrophil was found to be significantly higher in patients during the attack phase of this disease than in patients during the remission phase, in patients with other forms of uveitis and in normal controls. Collagenase was present in the collagenolytic enzyme, which showed high activity in the attack phase. The molecular weight of this enzyme was similar to that of mammalian neutrophil collagenase.

Immunoassay of serum alpha-1 antitrypsin level in uveitis

The serum alpha-1 antitrypsin level was measured in 60 patients with endogenous uveitis, 27 patients with phacoallergic endophthalmitis, 12 patients with phacolytic glaucoma, and 58 healthy subjects. Thirty-four patients with endogenous uveitis were also followed up for 6 months after treatment, and the serum alpha-1 antitrypsin level was measured again. There was a significant rise in the serum alpha-1 antitrypsin level in cases of endogenous uveitis and phacoallergic endophthalmitis but no alteration in cases of phacolytic glaucoma. Among the patients with endogenous uveitis the level was significantly raised in cases of anterior uveitis, but there was no change in cases of posterior uveitis. A significant rise was seen only in cases of acute anterior uveitis but not in chronic anterior uveitis. The serum alpha-1 antitrypsin level was unaltered in endogenous uveitis despite clinical improvement.

Decreased ecto-5'-nucleotidase activity in rabbit lymphocytes during experimental lens-induced uveitis

An experimental uveitis was produced by immunizing albino and pigmented rabbits with heterologous (rat) lens protein six times at two-week intervals. After sensitization the anterior lens capsules were disrupted in an operation. After operation the rabbits were examined repeatedly with a slit-lamp. On the seventh day after operation the animals were sacrificed and both eyes were enucleated. The inflammatory reaction in the uveal tract was verified histopathologically. Thymus and spleen lymphocytes were purified using BSA-gradients. Ecto-5'-nucleotidase (AMP-ase) activity on the intact lymphocytes was measured biochemically and B-cells were counted using the fluorescent anti-IgG technique. Purified spleen and thymus lymphocytes were also analyzed using transmission electron microscopy. The AMP-ase activity of purified spleen lymphocytes was significantly decreased in albino rabbits suffering from experimental lens-induced uveitis when compared to that observed in control animals. The AMP-ase activity was also decreased in pigmented rabbits suffering from a very mild uveitis. Moreover, a decreased AMP-ase activity was observed in albino rabbits which were only immunized but not operated on and did not show any signs of uveitis. Differences in neither the B-cell proportions nor the ultrastructure of the purified lymphocytes could be observed in any of these experimental groups. It is proposed that the biochemical change in spleen lymphocytes observed in the present work is a reflection of the general immunological state which in certain conditions may lead to uveitis.

Ecto 5'-nucleotidase activity in lymphocytes in cases of uveitis

This study attempts to demonstrate cellular reactivity in cases of uveitis. Lymphocyte AMPase activity was measured in 59 patients with uveitis of different types, all in the active stage. The patients were divided into 3 groups: 1) anterior uveitis with known disease, 2) anterior uveitis with unknown aetiology, and 3) posterior uveitis. The AMPase activity in peripheral lymphocytes from uveitis patients with known disease (group 1) was significantly decreased in comparison to lymphocytes from controls. Patients having endogenous uveitis (unknown aetiology, group 2) showed heterogeneity concerning their enzyme activity, and no significant changes were demonstrated. A subpopulation of patients with very low AMPase activity in the active stage of their disease could be defined. Patients with posterior uveitis showed no change in their lymphocyte AMPase activity. B-cells were also counted in cell suspension to verify that there was no selective change in the B-cells. Cell suspensions from patients with low and normal AMPase activities were studied by the electron microscope and found to have similar proportions of different types of mononuclear cells. Enzyme deficiencies in lymphocytes were associated with immunological disorders and would reflect dysfunction of lymphocytes. The heterogenous results from patients with endogenous uveitis were interpreted as showing cellular reactivity to ocular damage caused by a variety of mechanisms.

Quantification of ocular inflammation: evaluation of polymorphonuclear leucocyte infiltration by measuring myeloperoxidase activity

Myeloperoxidase (MPO) activity was measured in rabbit cornea and iris-ciliary body to quantitate the infiltration and accumulation of polymorphonuclear leucocytes (PMN's) following an inflammatory stimulus. Following injection of clove oil into the cornea, MPO activity could be detected in the cornea at 6 hr, reaching a maximum at 12 hr, and falling to non-detectable levels at 72 hr. MPO activity was only detected in the iris-ciliary body 24 hr after intracorneal clove oil injection. MPO activity in the iris-ciliary body increased in a dose-dependent manner following intravitreal injection of endotoxin. No MPO activity could be detected in cornea. Topical administration of dexamethasone inhibited MPO activity in cornea and iris-ciliary body 24 hr after intracorneal clove oil and intravitreal endotoxin injection, respectively. Measurement of MPO activity in ocular tissues could provide a useful tool to quantitatively evaluate the severity and time course of inflammation.