Andrew D. Dick

Experimental autoimmune uveoretinitis : a model system for immunointervention : a review

Experimental autoimmune uveoretinitis (EAU) is a useful model of human posterior uveitis and as such, permits the analysis of strategies for immuno-intervention. Modulation of the autoimmune response may be attempted at the stages of induction of EAU, during homing of autoreactive lymphocytes to the target organ, the retina, or during the effector stage of the disease. This paper presents a brief overview of current immuno-therapeutic modalities and assesses the usefulness for extrapolation to human disease.

Total dose and frequency of administration critically affect success of nasal mucosal tolerance induction

AIMS Nasal tolerance induction with autoantigens can effectively protect against a variety of experimental models of autoimmune disease. The aims of this study were to characterise the dosage and kinetics of inhibition of experimental autoimmune uveoretinitis (EAU) via intranasal administration of the uveitogenic antigen interphotoreceptor retinal binding protein (IRBP) in the murine model of IRBP induced EAU. METHODS B10RIII mice were tolerised by intranasal administration of IRBP either with a long term multiple low dose or a short term/high dosing regimen before subcutaneous immunisation with IRBP in complete Freunds adjuvant (CFA). On day 15 post-immunisation, mice were killed and eyes were removed for histological examination and quantification of inflammatory cell infiltration and degree of target organ (rod outer segment, ROS) destruction. RESULTS Nasal administration of multiple low doses of IRBP (1 μg or 3 μg IRBP per mouse per day for 10 days) significantly protected mice from IRBP induced EAU. Short term/high dose regimens were only effective when given either as a single or, at most, as two consecutive doses (40 μg per dose). Multiple doses in the range of 45–120 μg over 3 days afforded no protection. CONCLUSIONS These results indicate that both dose and frequency of intranasal antigen administration are pivotal to tolerance induction and subsequent suppression of T cell mediated autoimmune disease.

Induction or suppression of a B cell-specific response to self antigen in vivo is dependent upon dendritic cell activation via the TNF-alpha receptor at the time of antigen uptake.

In this study we show that the retinal autoantigen, S‐antigen, contains a functional TNF‐α homologous domain which stimulates maturation and differentiation of cultured dendritic cells (DC) or tissue DC via the p55 TNF‐α receptor. Tissue DC became more dendritiform in shape, and migrated into culture supernatant. S‐antigen also stimulated accumulation of cell surface MHC class II antigen with a corresponding loss of acidic intracellular vesicles, and induced IL‐1β and IL‐12 mRNA expression in cultured bone marrow‐derived DC. In addition, cultured splenic DC primed immune responses to S‐antigen in vivo in the absence of other, exogenous cytokine sources. DC pulsed with either retinal S‐antigen or another retinal autoantigen, interphotoreceptor retinoid binding protein (IRBP), were able to stimulate naive T cell proliferation in vitro, but only S‐antigen‐pulsed DC were able to induce an immune response in vivo and initiate antibody class switching. In contrast, IRBP‐pulsed DC had no detectable in vivo priming effect and IgG antibody levels remained suppressed even after immunization with IRBP in complete Freunds adjuvant. These results indicate that DC from the same precursor population can either induce or suppress a B cell‐specific response to self antigen in vivo, the outcome being dependent upon DC activation at the time of antigen uptake and presentation.

Antineutrophil Cytoplasmic Antibodies in Chronic Idiopathic Intraocular Inflammatory Disease

Antineutrophil cytoplasmic antibodies (ANCA) are found in the sera of patients with Wegeners granulomatosis and other systemic necrotising vasculitides. Antibody levels correlate closely with disease activity so that follow-up of ANCA titres might be helpful in guiding therapy. The authors assessed in a cohort of patients with chronic ocular inflammatory disease ANCA titres prospectively over a two-year period, by an indirect immunofluorescent technique. They found that sera from 10/64 patients (15.6%) stained positive for c-ANCA antibodies, and none stained for p-ANCA. Six c-ANCA positive patients had one or more clinical relapses (range one to three) during this study period. Each relapse correlated with a rise in ANCA titre. The remaining four patients who were found to have persistently low titres of c-ANCA had no clinical relapses. The authors conclude that although c-ANCA is only present in a small proportion of patients with idiopathic chronic intraocular inflammatory disease, the ANCA titre may be used to monitor disease activity in this group of patients. Further study to assess the potential of c-ANCA titres in predicting disease relapse is indicated, which in the future may minimise the side effects of currently used immunosuppressive therapies.

The use of lithium clearance studies in the early detection of cyclosporin A (CsA) nephrotoxicity:a protocol of renal function assessment with CsA therapy.

Cyclosporin A nephrotoxicity was studied with the use of lithium and creatinine clearance tests in 18 patients with chronic intraocular inflammation (duration of treatment 3-48 months). In 11 patients lithium clearance and fractional excretion of lithium were significantly reduced (compared with pretreatment levels) within the first six months of treatment. There was no significant change in either serum creatinine or creatinine clearance within this period. In 14/18 patients there was a significant reduction in lithium clearance and fractional excretion of lithium during the treatment period. 7 patients whose therapy was stopped because of continuing nephrotoxicity despite dose reduction, demonstrated some reversibility of renal function on cessation of cyclosporin A. We propose a protocol for the assessment of renal function in these patients so that with dose modulation the changes in these parameters can be minimised, reducing the risk of renal impairment, whilst maximising immunosuppressive treatment.

UVEITOGENIC EPITOPES OF RETINAL S-ANTIGEN ARE GENERATED IN VIVO VIA AN ALTERNATIVE ANTIGEN-PRESENTATION PATHWAY

We have found that different antigen‐processing pathways are involved in the induction of experimental autoimmune uveoretinitis (EAU) by the retinal autoantigens S‐antigen and interphotoreceptor retinoid‐binding protein (IRBP). Although in vitro T‐cell proliferative responses to IRBP were completely inhibited in the presence of irreversible cysteine protease inhibitors, no significant reduction of S‐antigen proliferative responses was found. Furthermore, acidic proteolysis of S‐antigen by the cysteine protease cathepsin B prior to immunization radically reduced pathogenicity (disease severity). In addition, in vitro processing of S‐antigen, but not IRBP, was also found to be resistant to the action of cycloheximide and lysosomotropic agents, inhibition of proliferation only occurring after extended exposure of antigen‐presenting cells to methyl amine or high concentrations of chloroquine. These data indicate that an alternative pathway of antigen processing exists for S‐antigen, which is independent of processing within the normal endo‐lysosomal pathway and that uveitogenic peptides of naturally processed S‐antigen bind to major histocompatibility complex class II antigens either at the cell surface or within very early endosomes where cathepsin B is inactive.