Characterization of amyloid in equine recurrent uveitis as AA amyloid.

The research studied two horses with chronic uveitis, a condition resulting in inflammation and redness in the eyes. The study revealed that these horses had an accumulation of a protein called amyloid AA within their eyes, suggesting that such a build-up could occur in horses with this condition.

Understanding the Context of the Research

• The research was conducted on two horses that exhibited chronic uveitis and displayed histological lesions – microscopic changes in tissue – denoting equine recurrent uveitis (ERU). ERU is a common cause of blindness in horses and is characterized by recurrent episodes of inflammation in the eyes.
• Uveitis in horses is akin to the redness and swelling humans feel in their eyes when they have an eye infection or when they develop certain types of eye diseases.

Microscopic Examination and Findings

• Microscopic examination of the horses’ ciliary body – the part of the eye that produces the clear fluid in the front of the eyeball – showed certain abnormalities. These included deposits of a protein called amyloid, certain formations within epithelial cells, and an abnormal presence of T lymphocytes, a type of white blood cell that plays a key role in the immune system.
• The deposits of amyloid were found lining the non-pigmented epithelium, which refers to the layer of cells lining various organs and cavities throughout the body that do not have pigment.

Ultrastructural Examination and Results

• An ultrastructural examination – a more detailed, high-resolution examination – was then conducted. This confirmed the presence of large amounts of these protein deposits.
• These deposits consisted of non-branching fibrils, consistent with the structure of amyloid, with a certain measurement in diameter.

Immunohistochemistry and Mass Spectrometry Results

• Immunohistochemistry, a process used to identify specific antigens (proteins) in cells of a tissue section, revealed strong positive labelling for AA amyloid. This indicates the presence of this specific type of amyloid protein.
• Subsequently, mass spectrometry – a technique that identifies the amount and type of chemicals present in a sample – further showed that the amyloid deposits consisted primarily of serum amyloid A1, a protein that plays a significant role in the body’s immune response to inflammation and infection.

Conclusions from the Study

• The findings of this research suggest that localized, intraocular (within the eye) AA amyloidosis – a condition where the protein amyloid AA builds up in tissues and organs – may occur in horses with recurrent uveitis.
• While this study only examined two horses, the findings contribute to the understanding of the pathophysiology of ERU and the associated inflammation. It suggests further avenues of research to comprehensively understand the relationship between ERU and amyloidosis.