IgA and secretory component (SC) in the third eyelid of domestic animals: a comparative study.

This research paper focuses on studying the presence and utility of immunoglobulin A (IgA) and secretory component (SC) in the third eyelid of different domestic animals. Through several analyses, the study asserts that the third eyelid plays a significant role in the secretory immune system in domestic animals.

Study Design

• The researchers focused on the third eyelid in domestic animals, known for its role in tear production and distribution, ocular debris removal, globe protection, and immunologic functions.
• They wanted to determine if IgA, a type of antibody found in tears, is produced locally. This antibody is typically produced by plasma cells in the lacrimal gland – the gland responsible for producing tears.
• They also studied the distribution of the Secretory Component (SC) in the third eyelid. SC is a part of secretory IgA and aids in transporting this antibody across mucosal surfaces.
• Eighty-three third eyelids from dogs, cats, pigs, cows, sheep, goats, and horses were used in this study. These specimens were cut length-wise, fixed overnight, and processed for a method known as the ABC technique, aimed to detect IgA and SC.

Results and Findings

• The study found that IgA-producing plasma cells were densely populated in certain areas of the third eyelid — subepithelial spaces of the surface epithelium as well as the nictitating gland (a part of the third eyelid), but their distribution varied amongst different species.
• Conversely, the SC was found predominantly in the glandular acinar (a part of the gland) and ductal epithelial cells, and different cell types of the surface epithelium. It was mainly located on the bulbar side of the nictitating membrane (the front edge of the third eyelid).

Conclusion

• The study concludes that most SC is likely produced by resident plasma cells located within the third eyelid and then transported through the surface epithelium and glandular duct cells by a process known as transcytosis.
• This makes the third eyelid a critical part of the secretory immune system in domestic animals, helping protect against ocular pathogens by producing antibodies.