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

Aims–Nasal tolerance induction with autoantigens can eVectively 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 Freund’s 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 eVective 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 aVorded 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. (Br J Ophthalmol 2001;85:739–744) Experimental autoimmune uveitis (EAU) is a T cell mediated disease that specifically targets the neural retina. Although EAU can be induced by a variety of retinal antigens in many diVerent animal strains, EAU in the mouse more closely resembles the pathology of a spectrum of human posterior segment intraocular inflammatory (PSII) conditions including sympathetic ophthalmia, sarcoidosis, and birdshot retinochoroidopathy. As a result of the close clinicopathological correlation of EAU in mice to human PSII, the model has been extensively used for the investigation of underlying immunological mechanisms and furthermore for the development of novel therapeutic approaches. Mucosal administration of autoantigens results in the development of a state of peripheral immunological tolerance. Mucosal tolerance induction by oral or nasal antigen administration of autoantigen eVectively prevents several experimental disease models, including experimental autoimmune encephalomyelitis (EAE), experimental myasthenia gravis (EAMG), collagen induced arthritis (CIA), insulin dependent diabetes mellitus in the NOD mouse, and EAU. Despite such success, the results of trials in autoimmune diseases in humans are equivocal. For example, in both multiple sclerosis and uveitis administration of bovine myelin basic protein and retinal antigens, respectively, failed to show conclusively any clinical significant improvement. 13 This may have been due in part to our fundamental lack of understanding of the mechanisms of tolerance with regard to induction protocol, dosage, and frequency of therapy. To date several mechanisms of mucosal tolerance induction have been proposed, including T cell anergy, generation of regulatory Th3 (TGF-â producing) cells, or CD8+ T cells 16 and ãä T cells, 18 all of which are dependent upon the dose and route of antigen delivery. Recent data have in part shifted emphasis towards the central role of CD4+ T cells and IL-2, 21 including both peptide aYnity for MHC class II binding as well as inherent hierarchical ability of T cell epitopes to induce tolerance. With respect to CD4+ T cells, mucosal administration of autoantigen results in early activation and subsequent apoptosis of T cell populations. Studies of transgenic (Tg) mice have shown that the success of tolerance therapy is dependent upon the duration of therapy that in turn is dependent upon the precursor frequency of antigen specific T cells. In both Tg OVA and AC1-9TCR Tg mice following intranasal antigen delivery early activation followed by a transient and incomplete deletion of T cells was observed. Residual T cells remained unresponsive, although in the EAE model, they produced IL-10. Such results are comparable with our previous data in EAU in rat showing that, following intranasal retinal antigen delivery, lymph node cells were activated (IFN-ã spurt) and on further antigen challenge increased levels of apoptosis were noted within the draining lymph node. Although regulatory cells were generated, tolerance could only be transferred via spleen cells. Moreover, the cells that did infiltrate the retina in tolerised animals produced IL-10. Br J Ophthalmol 2001;85:739–744 739 Department of Ophthalmology, University of Aberdeen Medical School Foresterhill, Aberdeen AB25 2ZD, UK