A novel pathogenic RBP-3 peptide reveals epitope spreading in persistent experimental autoimmune uveoretinitis

CTLA-4 expression on tregs is needed for suppression of autoimmune uveitis

Uveitis is a leading cause of blindness in the world and autoimmune uveitis is an ocular tissue specific autoimmune disease. Utilizing experimental autoimmune uveitis (EAU), we can interrogate different immune responses in the mouse that are relevant to the human disease. cytotoxic T-lymphocyte antigen 4 (CTLA-4) is an immune checkpoint molecule that has different roles depending on the target tissue. In this work we investigate the role of CTLA-4 on CD4 T cells in ocular tissue during EAU. We find that CTLA-4 is needed for both the severity of disease but also timely resolution of disease. Regulatory T cells (Tregs) that emerge in the spleen during resolution of EAU require CTLA-4 to suppress disease, but ocular Tregs that emerge in the eye do not require CTLA-4 to suppress disease. This report provides an additional understanding of CTLA-4 on Tregs that is specific for ocular tissue. The implications of this work are that circulating Tregs in uveitis patients may require CTLA-4 to suppress ocular inflammation but once in the eye the function of CTLA-4 is dispensable.

New insights into the phenomenon of remissions and relapses in autoimmune diseases and the puzzle of benign autoantibodies in healthy individuals

The onset and relapse of autoimmune diseases (AIDs) are triggered by autoimmune attacks on target tissues. However, symptoms are unlikely to appear if damaged cells are rapidly replaced. Addressing the implications of this premise, the present work examines the balance between target tissue destruction and recovery rates as a key factor in the mechanisms of remissions and relapses in AIDs. The theory, supported by published clinical data, suggests that remissions are improbable in AIDs characterized by slow target tissue recovery. Conversely, a high recovery rate is a necessary (though not sufficient) condition for cycles of remission and relapse in AIDs. A high recovery rate of target tissue explains the tendency for remitting-relapsing disease, the likelihood of detecting autoantibodies in healthy individuals and the responsiveness to immunosuppressive drug treatments. Analyzing specific AIDs through the balance of tissue destruction and recovery yields several insights. For example, the difference between androgenic alopecia, a non-remitting-relapsing disease and alopecia areata, a remitting-relapsing AID, is elucidated. A new mechanism underlying relapses and remissions in alopecia areata based on hair follicle regeneration rate is proposed. It is suggested that mild Graves' disease and remitting Hashimoto's thyroiditis would be responsive to corticosteroids or immunosuppressant treatment, unlike more severe forms of these diseases. Additionally, it is proposed that the transition from remitting-relapsing multiple sclerosis to secondary progressive multiple sclerosis is associated with the depletion of brain compensatory reserves. Notably, it is concluded that exercise will not play a neuroprotective role in secondary progressive multiple sclerosis.

The quest for early detection of retinal disease: 3D CycleGAN-based translation of optical coherence tomography into confocal microscopy

Optical coherence tomography (OCT) and confocal microscopy are pivotal in retinal imaging, offering distinct advantages and limitations. In vivo OCT offers rapid, noninvasive imaging but can suffer from clarity issues and motion artifacts, while ex vivo confocal microscopy, providing high-resolution, cellular-detailed color images, is invasive and raises ethical concerns. To bridge the benefits of both modalities, we propose a novel framework based on unsupervised 3D CycleGAN for translating unpaired in vivo OCT to ex vivo confocal microscopy images. This marks the first attempt to exploit the inherent 3D information of OCT and translate it into the rich, detailed color domain of confocal microscopy. We also introduce a unique dataset, OCT2Confocal, comprising mouse OCT and confocal retinal images, facilitating the development of and establishing a benchmark for cross-modal image translation research. Our model has been evaluated both quantitatively and qualitatively, achieving Fréchet inception distance (FID) scores of 0.766 and Kernel Inception Distance (KID) scores as low as 0.153, and leading subjective mean opinion scores (MOS). Our model demonstrated superior image fidelity and quality with limited data over existing methods. Our approach effectively synthesizes color information from 3D confocal images, closely approximating target outcomes and suggesting enhanced potential for diagnostic and monitoring applications in ophthalmology.

Combined Deficiency of the Melanocortin 5 Receptor and Adenosine 2A Receptor Unexpectedly Provides Resistance to Autoimmune Disease in a CD8+ T Cell-Dependent Manner

Regulatory immunity that provides resistance to relapse emerges during resolution of experimental autoimmune uveitis (EAU). This post-EAU regulatory immunity requires a melanocortin 5 receptor (MC5r)-dependent suppressor antigen presenting cell (APC), as shown using a MC5r single knock-out mouse. The MC5r-dependent APC activates an adenosine 2A receptor (A2Ar)-dependent regulatory Treg cell, as shown using an A2Ar single knock-out mouse. Unexpectedly, when MC5r^-/- post-EAU APC were used to activate A2Ar^-/- post-EAU T cells the combination of cells significantly suppressed EAU, when transferred to EAU mice. In contrast, transfer of the reciprocal activation scheme did not suppress EAU. In order to explain this finding, MC5r^-/-A2Ar^-/- double knock-out (DKO) mice were bred. Naïve DKO mice had no differences in the APC populations, or inflammatory T cell subsets, but did have significantly more Treg cells. When we examined the number of CD4 and CD8 T cell subsets, we found significantly fewer CD8 T cells in the DKO mice compared to WT and both single knock-out mice. DKO mice also had significantly reduced EAU severity and accelerated resolution. In order to determine if the CD8 T cell deficiency contributed to the resistance to EAU in the DKO mice, we transferred naïve CD8 T cells from WT mice, that were immunized for EAU. Susceptibility to EAU was restored in DKO mice that received a CD8 T cell transfer. While the mechanism that contributed to the CD8 T cell deficiency in the DKO mice remains to be determined, these observations indicate an importance of CD8 T cells in the initiation of EAU. The involvement of CD4 and CD8 T cells suggests that both class I and class II antigen presentation can trigger an autoimmune response, suggesting a much wider range of antigens may trigger autoimmune disease.

Molecular Mimicry and Uveitis

Molecular or antigenic mimicry is a term for the similarity of different antigens, which can be confused by the immune system. Antigen recognition by antibodies and T cell receptors is specific, but not restricted to a single antigen. Both types of receptors specifically recognize antigens and are expressed with a very high but still restricted variability compared to the number of different antigens they potentially could bind. T cell receptors only can bind to antigen peptides presented on certain self-MHC-molecules by screening only some amino acid side chains on both the presented peptides and the MHC molecule. The other amino acids of the peptide are not directly perceived by the T cell, offering the opportunity for a single T cell to recognize a variety of different antigens with the same receptor, which significantly increases the immune repertoire. The immune system is usually tolerant to autoantigens, especially to those of immune privileged sites, like the eye. Therefore, autoimmune diseases targeting these organs were hard to explain, unless a T cell is activated by an environmental peptide (e.g. pathogen) that is similar, but not necessarily identical with an autoantigen. Here we describe antigenic mimicry of retinal autoantigens with a variety of non-ocular antigens resulting in the induction of intraocular inflammation. T cells that are activated by mimotopes outside of the eye can pass the blood-retina barrier and enter ocular tissues. When reactivated in the eye by crossreaction with autoantigens they induce uveitis by recruiting inflammatory cells.

Quantitative proteomic analysis of rat retina with experimental autoimmune uveitis based on tandem mass tag (TMT) peptide labeling coupled with LC-MS/MS

Uveitis is a recurrent, inflammatory eye disease that occurs in the retina, iris, ciliary body and choroid. Currently, the detailed mechanism is still unclear. Proteomics can offer a powerful set of tools for the direct high-throughput study and a key contribution to the understanding of protein functions. This approach can also allow us to compare the protein profiling of the cells in healthy and diseased states that can be used to identify proteins associated with disease development and progression. In the present study, we first established an autoimmune uveitis (EAU) rat model. On day 12 after immunization, we isolated the rat retinas from both normal and EAU animals to collect total proteins. Using tandem mass tag (TMT) peptide labeling coupled with LC-MS/MS quantitative proteomics technique, we identified the differentially expressed proteins in EAU rat retinas, performed bioinformatics analyses, validated the expression of the COX1, NADH1, C3, and C9 proteins, and determined the adenosine triphosphate (ATP) levels. The results indicated that there were 190 upregulated and 103 downregulated proteins in EAU rat retinas. Bioinformatics analysis revealed the differentially expressed proteins were mainly involved in acute inflammatory response, visual perception and eye photoreceptor cell differentiation that were mainly related to complement and coagulation cascades, phagosome, PI3K-Akt signaling, and metabolic pathways. In conclusion, based on the TMT-based quantitative proteomics technique, the differentially expressed proteins in EAU rat retinas were mainly associated with complement and coagulation cascades and metabolic pathways. Our findings will facilitate the understanding of the pathogenesis of uveitis and will be useful for subsequent studies.

Stochastic dynamics in a time-delayed model for autoimmunity

In this paper we study interactions between stochasticity and time delays in the dynamics of immune response to viral infections, with particular interest in the onset and development of autoimmune response. Starting with a deterministic time-delayed model of immune response to infection, which includes cytokines and T cells with different activation thresholds, we derive an exact delayed chemical master equation for the probability density. We use system size expansion and linear noise approximation to explore how variance and coherence of stochastic oscillations depend on parameters, and to show that stochastic oscillations become more regular when regulatory T cells become more effective at clearing autoreactive T cells. Reformulating the model as an Itô stochastic delay differential equation, we perform numerical simulations to illustrate the dynamics of the model and associated probability distributions in different parameter regimes. The results suggest that even in cases where the deterministic model has stable steady states, in individual stochastic realisations, the model can exhibit sustained stochastic oscillations, whose variance increases as one gets closer to the deterministic stability boundary. Furthermore, in the regime of bi-stability, whereas deterministically the system would approach one of the steady states (or periodic solutions) depending on the initial conditions, due to the presence of stochasticity, it is now possible for the system to reach both of those dynamical states with certain probability. Biological significance of this result lies in highlighting the fact that since normally in a laboratory or clinical setting one would observe a single individual realisation of the course of the disease, even for all parameters characterising the immune system and the strength of infection being the same, there is a proportion of cases where a spontaneous recovery can be observed, and similarly, where a disease can develop in a situation that otherwise would result in a normal disease clearance.

Features of ectopic lymphoid-like structures in human uveitis

Persistent non-infectious uveitis has a significant morbidity, but the extent to which this is accompanied by inflammation driven remodelling of the tissue is unclear. To address this question, we studied a series of samples selected from two ocular tissue repositories and identified 15 samples with focal infiltration. Eleven of fifteen contained lymphocytes, both B cells (CD20 positive) and T cells (CD3 positive). In 20% of the samples there was evidence of ectopic lymphoid like structures with focal aggregations of B cells and T cells, segregated into anatomically different adjacent zones. To investigate inflammation in the tissue, an analysis of 520 immune relevant transcripts was carried out and 24 genes were differentially upregulated, compared with control tissue. Two of these (CD14 and fibronectin) were increased in ocular inflammation compared to control immune tissue (tonsil). We demonstrate that in a significant minority of patients, chronic persistent uveitis leads to dysregulation of ocular immune surveillance, characterized by the development of areas of local ectopic lymphoid like structures, which may be a target for therapeutic intervention directed at antibody producing cells.

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Active inflammation continues in cases of persistent uveitis.

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Some patients develop ectopic lymphoid-like structure.

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In these cases targeting B cells may be beneficial.

Are Anti-Retinal Autoantibodies a Cause or a Consequence of Retinal Degeneration in Autoimmune Retinopathies?

Autoantibodies (AAbs) against various retinal proteins have been associated with vision loss in paraneoplastic and non-paraneoplastic autoimmune retinopathies (AR). There are two major paraneoplastic syndromes associated anti-retinal AAbs, cancer-associated retinopathy (CAR), and melanoma-associated retinopathy. Some people without a cancer diagnosis may present symptoms of CAR and have anti-retinal AAbs. The etiology and pathogenesis of those entities are not fully understood. In this review, we provide evidence for the role of AAbs in retinal death and degeneration. Studies of epitope mapping for anti-recoverin, anti-enolase, and anti-carbonic anhydrase II revealed that although patients' AAbs may recognize the same retinal protein as normal individuals they bind to different molecular domains, which allows distinguishing between normal and diseased AAbs. Given the great diversity of anti-retinal AAbs, it is likely some antibodies have greater pathogenic potential than others. Pathogenic, but not normal antibodies penetrate the target cell, reach their specific antigen, induce apoptosis, and impact retinal pathophysiology. Photoreceptors, dying by apoptosis, induced by other than immunologic mechanisms produce substantial amounts of metabolic debris, which consequently leads to autoimmunization and enhanced permeability of the blood-retinal barrier. AAbs that were made as a part of anti-cancer response are likely to be the cause of retinal degeneration, whereas others, generated against released antigens from damaged retina, contribute to the progression of retinopathy. Altogether, AAbs may trigger retinal degeneration and may also exacerbate the degenerative process in response to the release of sequestered antigens and influence disease progression.

Stochastic Effects in Autoimmune Dynamics

Among various possible causes of autoimmune disease, an important role is played by infections that can result in a breakdown of immune tolerance, primarily through the mechanism of “molecular mimicry”. In this paper we propose and analyse a stochastic model of immune response to a viral infection and subsequent autoimmunity, with account for the populations of T cells with different activation thresholds, regulatory T cells, and cytokines. We show analytically and numerically how stochasticity can result in sustained oscillations around deterministically stable steady states, and we also investigate stochastic dynamics in the regime of bi-stability. These results provide a possible explanation for experimentally observed variations in the progression of autoimmune disease. Computations of the variance of stochastic fluctuations provide practically important insights into how the size of these fluctuations depends on various biological parameters, and this also gives a headway for comparison with experimental data on variation in the observed numbers of T cells and organ cells affected by infection.