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DH Anderson; Substructural Vesicles Within Drusen Are Putative Primary Sites Of Complement Activation . Invest. Ophthalmol. Vis. Sci. 2002;43(13):2793.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Terminal complement components (C5,C5b-9)and several complement inhibitors are ubiquitous drusen components. This implies that complement activation may be a key element in drusen formation; but the specific complement activator(s) and activation pathway are unknown. The classical pathway is triggered by the binding of immune complexes to C1q. Alternative and lectin pathways that are antibody-independent also exist. Other molecules that interact with, or substitute for, C1q can also activate complement directly. Methods: The RPE/choroid was excised from human donor eyes with and without drusen. Vibratome sections were examined using differential interference contrast (DIC) and confocal microscopy (CM). Some sections were re-embedded and examined by electron microscopy (TEM). For CM, sections were probed with: a.) monoclonal antibodies (Ab) raised against activation-specific fragments of complement C3, HLA-DR antigen, and IgG; b.) Abs to mitochondrial, Golgi, and lysosomal proteins; c.) lipophilic dyes; and d.) nucleic acid-binding dyes. Results: Drusen contain substructural vesicular elements (2-10 µm diameter) that consist of concentric lamellae. DIC shows that the larger vesicles contain a dense core, one or more inner rings, and an outer shell. The vesicles are not lipid-rich, as shown the lack of DiI binding; nor do they stain with nucleic acid-binding dyes. TEM indicates that the vesicles are distinct from drusen "cores". The outer shell is electron dense while the inner rings contain fibrillar-like material. Vesicles are unlabeled with Abs to prominent drusen-associated molecules including vitronectin, amyloid P component, IgG, and Apo E. However, they display strong and specific labeling using Abs to: a.) fragments of complement C3 that are deposited at primary activation sites; b.) a known complement activator; c.) HLA-DR; and d.) endosomal/lysosomal markers. Conclusion: Substructural vesicles within drusen contain C3 fragments that mark primary sites of complement activation, and potential complement activating molecules. The vesicles are likely by-products of degenerate RPE cells that contain molecules highly resistant to degradation. Support: EY11521(DHA) and EY11527(LVJ)
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