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Distribution of complement in the sclera
O Brawman-Mintzer1, B J Mondino, F J Mayer
1Department of Ophthalmology, UCLA School of Medicine.
Insights
The anterior sclera has higher levels of C1, initiating the complement cascade, potentially explaining why immune-related scleritis is more common anteriorly. The posterior sclera shows higher levels of other complement factors and proteins, suggesting better vascularization.
Area of Science:
- Ocular immunology
- Complement system biology
- Scleral tissue analysis
Background:
- The sclera, the outer protective layer of the eye, plays a role in ocular immunity.
- Immune complex-mediated diseases can affect the sclera, leading to conditions like scleritis.
- Differential distribution of immune components between anterior and posterior sclera is not fully understood.
Purpose of the Study:
- To compare the hemolytic activities and protein levels of complement components in the anterior and posterior sclera.
- To investigate the potential correlation between complement distribution and the prevalence of anterior scleritis.
Main Methods:
- Hemolytic activity assays for complement components C1, C4, C2, C3, C5, C6, and C7.
- Radial immunodiffusion to quantify Factor B, IgG, IgA, and albumin levels.
- Comparison of protein concentrations between anterior and posterior scleral tissues.
Main Results:
- Complement levels (except C1) and protein levels (IgG, IgA, albumin) were significantly higher in the posterior sclera compared to the anterior sclera.
- The anterior sclera exhibited significantly higher levels of C1, the initial component of the classical complement pathway.
- These findings suggest differential vascular supply and immune surveillance between the two scleral regions.
Conclusions:
- The posterior sclera appears to have a more robust vascular supply, supporting higher concentrations of various complement factors and proteins.
- The elevated C1 concentration in the anterior sclera may facilitate complement activation, contributing to its higher susceptibility to immune complex-related scleritis.
- Understanding regional scleral immune differences is crucial for explaining disease predilection and developing targeted therapies.
Abstract:
In the present study, we compared hemolytic activities of C1, C4, C2, C3, C5, C6 and C7 in the anterior and posterior sclera. Additionally, we used radial immunodiffusion to measure levels of Factor B, IgG, IgA and albumin in the anterior and posterior sclera. Except for C1, complement levels were significantly higher in the posterior than anterior sclera. Additionally, levels of immunoglobulins as well as albumin were significantly higher in the posterior than anterior sclera. These results suggest that the posterior sclera has a better adjacent vascular supply than the anterior sclera. On the other hand, the results of this study show that the anterior sclera has more C1, the recognition unit of the classical pathway, than the posterior sclera. Because there is nearly twice as much C1 in the anterior sclera, it may be easier for antigen-antibody complexes, whether formed in the sclera itself or derived from the neighboring vessels, to set off the complement cascade in the anterior sclera. This finding may help explain why scleritis associated with immune complex disease is more common in the anterior than posterior sclera.