Amino acid regions 357-368 and 418-427 of Streptococcus pyogenes 60kDa heat shock protein are recognized by antibodies from glaucomatous patient sera

Role of T cell-induced autoimmune response in the pathogenesis of glaucoma

PURPOSE

This review aims to elucidate the role of T cell-induced autoimmune responses in the pathogenesis of glaucoma, focusing on the immunological changes contributing to retinal ganglion cell (RGC) damage.

METHODS

A comprehensive review of recent studies examining immunological mechanisms in glaucoma was conducted. This included analyses of T cell interactions, heat shock proteins (HSPs), and resultant autoimmune responses. Key findings from experimental models and clinical observations were synthesized to present a coherent understanding of immune dynamics in glaucoma.

RESULTS

Glaucoma is a neurodegenerative disease marked by optic nerve atrophy and irreversible vision loss due to RGC damage. The disease is etiologically heterogeneous, with multiple risk factors and pathogenic mechanisms. Recent research highlights the dual immunomodulatory role of T cells in immune protection and injury. T cells, pre-sensitized by bacterial HSPs, can cross-react with endogenous HSPs in RGCs under stress, leading to autoimmune damage. Elevated levels of HSP autoantibodies and abnormal T cell activity have been observed in glaucoma patients, indicating a significant autoimmune component in disease progression.

CONCLUSIONS

T cell-induced autoimmune responses are crucial in the pathogenesis of glaucoma, contributing to RGC degeneration beyond the effects of elevated intraocular pressure. Understanding these immunological mechanisms is vital for developing targeted neuroprotective therapies for glaucoma.

Autoantigens in the trabecular meshwork and glaucoma-specific alterations in the natural autoantibody repertoire

OBJECTIVES

Primary open-angle glaucoma (POAG) is a neurodegenerative disorder leading to a gradual vision loss caused by progressive damage to the optic nerve. Immunological processes are proposed to be involved in POAG pathogenesis. Altered serological autoantibody levels have been frequently reported, but complete analyses of the natural autoantibodies with respect to disease-related alterations are scarce. Here, we provide an explorative analysis of pathways and biological processes that may involve naturally immunogenic proteins and highlight POAG-specific alterations.

METHODS

Mass spectrometry-based antibody-mediated identification of autoantigens (MS-AMIDA) was carried out in healthy and glaucomatous trabecular meshwork (TM) cell lines, using antibody pools purified from serum samples of 30 POAG patients and 30 non-glaucomatous subjects. Selected antigens were validated by protein microarray (n = 120). Bioinformatic assessment of identified autoantigens, including Gene Ontology (GO) enrichment analysis and protein-protein interaction networks, was applied.

RESULTS

Overall, we identified 106 potential autoantigens [false discovery rate (FDR) < 0.01], from which we considered 66 as physiological targets of natural autoantibodies. Twenty-one autoantigens appeared to be related to POAG. Bioinformatic analysis revealed that the platelet-derived growth factor receptor beta (PDGFRB) pathway involved in TM fibrosis was particularly rich in POAG-related antigens. Antibodies to threonine-tRNA ligase (TARS), component 1 Q subcomponent-binding protein (C1QBP) and paraneoplastic antigen Ma2 (PNMA2) showed significantly (P < 0.05) higher levels in POAG patients as validated by protein microarray.

CONCLUSION

This study provides new insights into autoimmunity in health and glaucoma. Bioinformatic analysis of POAG-related autoantigens showed a strong association with the PDGFRB pathway and also increased levels of PNMA2, TARS, and C1QBP autoantibodies in the serum of POAG patients as potential glaucoma biomarkers.

Role of Heat Shock Proteins in Glaucoma

Glaucoma, one of the most common causes of blindness worldwide, is a multifactorial neurodegenerative disease characterized by damage of retinal ganglion cells and optic nerve degeneration. However, the exact mechanism leading to glaucoma is still not understood. Evidences suggest an immunological involvement in the pathogenesis. Among other immune responses, altered autoantibody patterns were found in glaucoma patients. Especially elevated antibody levels against heat shock proteins (HSPs), like HSP27 or HSP60, were identified. In an animal model, an immunization with these HSPs induced a pressure-independent retinal ganglion cell degeneration and axon loss, hence mimicking glaucoma-like damage. In addition, development of autoreactive antibodies, as well as a glia and T-cell activation, were described in these animals. Recently, we noted that intravitreal HSP27 injection likewise led to a degeneration of retinal ganglion cells and their axons. Therefore, HSP27 might have a direct damaging effect on retinal cells, and might play a key role in glaucoma.

Biomarkers of primary open-angle glaucoma

Primary open-angle glaucoma (POAG) is a primary neuronal disease of the optic nerve without a definable cause, and is often associated with increased intraocular pressure. Worldwide, POAG is the second leading cause of blindness; there are 45 million people today with POAG and bilateral blindness is present in 4.5 million of these. In order to elucidate the possible etiologic factors in POAG, we have cataloged all known biomarkers in the aqueous humor, trabecular meshwork, optic nerve and blood into four categories, namely extracellular matrix (ECM), cell signaling molecules, aging/stress and immunity-related changes. We present a theoretical model to show possible signaling pathways of the ECM, cell signaling and innate immune response through activation of Toll-like receptor 4. Our article suggests that ECM and innate immune biomarkers are the lead candidates for developing the 'POAG biomarker signature'. We suggest that current research is critical to pinpoint the causes of the disease so that new treatment modalities can become available for better regulation of the intraocular pressure and neuroprotection of the optic nerve.

The Immunology of Glaucoma

The presence of specific antibodies and T cells that are specific in patients with glaucoma supports the idea that the immune system may play an important role in the initiation and/or sustainment of glaucomatous optic neuropathy, at least in some patients. At present, our understanding regarding immunological mechanisms associated with glaucomatous optic neuropathy is far from satisfactory. In this review, we examined evidence suggesting involvement of autoimmune responses in the pathogenesis of glaucoma. These include detection of autoantibodies and T cells and expression of cytokines and stress proteins in patients with glaucoma. Although immune responses are thought to be detrimental, some responses may exert a protective effect against neurodegenerative damage. Likely, the balance between positive and negative regulators determines the survival or demise of cells. It is vital that research continues to elucidate the roles of the immune system in glaucomatous neurodegeneration and the possibility of alternative modalities of treatment. These studies may also provide valuable molecular biomarkers for the diagnosis and identification of a specific cohort of patients with glaucoma, that is, those with normal-tension glaucoma.