Uveitis in mouse and man

Autoimmune and autoinflammatory mechanisms in uveitis

The eye, as currently viewed, is neither immunologically ignorant nor sequestered from the systemic environment. The eye utilises distinct immunoregulatory mechanisms to preserve tissue and cellular function in the face of immune-mediated insult; clinically, inflammation following such an insult is termed uveitis. The intra-ocular inflammation in uveitis may be clinically obvious as a result of infection (e.g. toxoplasma, herpes), but in the main infection, if any, remains covert. We now recognise that healthy tissues including the retina have regulatory mechanisms imparted by control of myeloid cells through receptors (e.g. CD200R) and soluble inhibitory factors (e.g. alpha-MSH), regulation of the blood retinal barrier, and active immune surveillance. Once homoeostasis has been disrupted and inflammation ensues, the mechanisms to regulate inflammation, including T cell apoptosis, generation of T_reg cells, and myeloid cell suppression in situ, are less successful. Why inflammation becomes persistent remains unknown, but extrapolating from animal models, possibilities include differential trafficking of T cells from the retina, residency of CD8⁺ T cells, and alterations of myeloid cell phenotype and function. Translating lessons learned from animal models to humans has been helped by system biology approaches and informatics, which suggest that diseased animals and people share similar changes in T cell phenotypes and monocyte function to date. Together the data infer a possible cryptic infectious drive in uveitis that unlocks and drives persistent autoimmune responses, or promotes further innate immune responses. Thus there may be many mechanisms in common with those observed in autoinflammatory disorders.

Detection of choroid- and retina-antigen reactive CD8(+) and CD4(+) T lymphocytes in the vitreous fluid of patients with birdshot chorioretinopathy

Birdshot chorioretinopathy (BSCR), a progressive form of non-infectious uveitis, is the strongest HLA-associated disease described to date, with >95% of the patients displaying HLA-A29. Since indirect evidence indicates the involvement of T cells in the etiopathology of the disease, we now isolated, cultured and analyzed the vitreous fluid-infiltrating T cells from two BSCR patients with respect to their phenotype, cytokine profile, clonal distribution and antigen specificity. Phenotypic analyses revealed the predominant presence of both CD4(+) and CD8(+) T cells in vitreous fluid. Further analyses on short term expanded and cloned T cells suggested that eye-infiltrating T cells generally displayed a Th1 like cytokine profile with secretion of high levels of IFN-γ and TNF-α. In one patient an oligoclonal CD4(+) and CD8(+) T cell infiltration, with a moderate to strongly skewed TCR Vβ usage was suggestive for an antigen driven infiltration/expansion. Indeed, a number of intraocular CD4(+) and CD8(+) T cells responded to crude retinal and choroidal lysates. These results, which demonstrate for the first time the existence of eye-antigen-specific T cells in the vitreous fluid of BSCR patients, substantiate the current view on the role of eye-antigen specific T cells in the etiopathology of BSCR.

Functional validation of a human CAPN5 exome variant by lentiviral transduction into mouse retina

Exome sequencing indicated that the gene encoding the calpain-5 protease, CAPN5, is the likely cause of retinal degeneration and autoimmune uveitis in human patients with autosomal dominant neovascular inflammatory vitreoretinopathy (ADNIV, OMIM #193235). To explore the mechanism of ADNIV, a human CAPN5 disease allele was expressed in mouse retinas with a lentiviral vector created to express either the wild-type human (h) CAPN5 or the ADNIV mutant hCAPN5-R243L allele under a rhodopsin promoter with tandem green fluorescent protein (GFP) expression. Vectors were injected into the subretinal space of perinatal mice. Mouse phenotypes were analyzed using electroretinography, histology and inflammatory gene expression profiling. Mouse calpain-5 showed high homology to its human ortholog with >98% sequence identity that includes the ADNIV mutant residue. Calpain-5 protein was expressed in the inner and outer segments of the photoreceptors and in the outer plexiform layer. Expression of the hCAPN5-R243L allele caused loss of the electroretinogram b-wave, photoreceptor degeneration and induction of immune cell infiltration and inflammatory genes in the retina, recapitulating major features of the ADNIV phenotype. Intraocular neovascularization and fibrosis were not observed during the study period. Our study shows that expression of the hCAPN5-R243L disease allele elicits an ADNIV-like disease in mice. It further suggests that ADNIV is due to CAPN5 gain-of-function rather than haploinsufficiency, and retinal expression may be sufficient to generate an autoimmune response. Genetic models of ADNIV in the mouse can be used to explore protease mechanisms in retinal degeneration and inflammation as well as preclinical therapeutic testing.

Bowman lecture on the role of inflammation in degenerative disease of the eye

Inflammation, in the pathogenesis of many diseases previously thought to be strictly genetic, degenerative, metabolic, or endocrinologic in aetiology, has gradually entered the framework of a general mechanism of disease. This is exemplified by conditions such as Parkinson's disease, Alzheimer's disease, atherosclerosis, diabetes, and the more recently described Metabolic Syndrome. Chronic inflammatory processes have a significant, if not primary role, in ophthalmic diseases, particularly in retinal degenerative diseases. However, inflammation itself is not easy to define, and some aspects of inflammation may be beneficial, in a process described as 'para-inflammation' by Medhzitov. In contrast, the damaging effects of inflammation, mediated by pro-inflammatory macrophages through activation of the intracellular protein-signalling complexes, termed inflammasomes, are well recognised and are important therapeutic targets. In this review, the range of inflammatory processes in the eye is evaluated in the context of how these processes impact upon retinal degenerative disease, particularly diabetic retinopathy and age-related macular degeneration.