Vitreal IgM autoantibodies target neurofilament medium in a spontaneous model of autoimmune uveitis.

The research paper investigates the role of IgM autoantibodies in equine recurrent uveitis (ERU), a spontaneous disease model, where they were found to target neurofilament medium (NF-M), a protein expressed in the horse’s retina. It suggests the prevalence of IgM-dominated response might be significant in understanding both ERU and the similar human disease, autoimmune uveitis.

Research Goals

• The study aims to investigate the role of IgM autoantibodies in equine recurrent uveitis (ERU). Despite previous studies showing the presence of IgG autoantibodies in ERU cases, the activity and role of IgM autoantibodies have been less explored.
• The researchers also aim to examine the binding specificity of IgM autoantibodies to proteins expressed within the eye.

Methods

• To examine the IgM autoantibody responses, vitreous samples (a gel-like substance that fills most of the space in the eye) from both healthy and ERU-affected horses were analyzed using a two-dimensional Western blot analysis with horse retinal tissue as an antigen source.
• Through this, a candidate protein named Neurofilament Medium (NF-M) was identified via mass spectrometry. Its validity was further checked via enzyme-linked immunosorbent assay (ELISA).
• Immunohistochemistry was then performed on both healthy and ERU-affected retinal sections to analyze NF-M expression.

Results

• The study found that NF-M was specifically targeted by vitreal IgM autoantibodies in about 44% of the ERU cases studied, while an anti-NF-M IgG response was detected only in 8% of the ERU samples. This suggested a persistent IgM response in ERU cases.
• In healthy horse retinas, NF-M was mostly found in the retinal ganglion cells and their processes, with additional staining in the outer plexiform layer. However, in ERU-affected retinas, its expression notably decreased, remaining only within the nerve fiber layer.

Conclusions

• The research concludes that intraocular anti-NF-M IgM autoantibodies occur with high prevalence in ERU cases.
• The predominance of IgM response over IgG may indicate a thymus-independent response to NF-M, which demands further investigation in ERU and its human counterpart, autoimmune uveitis.