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Complement-regulator factor H and related proteins in otitis media with effusion
M Närkiö-Mäkelä1, J Hellwage, O Tahkokallio
1Department of Bacteriology and Immunology, University of Helsinki, Helsinki, Finland.
Insights
Otitis media with effusion (OME) involves chronic inflammation driven by the complement system. This study found that middle ear fluid in OME patients disrupts complement regulation, leading to excessive inflammation.
Area of Science:
- Immunology
- Otolaryngology
- Molecular Biology
Background:
- Otitis media with effusion (OME) is a prevalent childhood condition characterized by chronic inflammation.
- The complement (C) system's pro-inflammatory activity is implicated in OME pathogenesis.
- The precise mechanisms driving complement activation within middle ear effusion (MEE) remain unclear.
Purpose of the Study:
- To investigate the role of the alternative complement pathway (AP) in OME.
- To identify regulatory molecules of the AP within MEE.
- To elucidate how MEE components influence complement system dysregulation in OME.
Main Methods:
- Complement Bb fragment ELISA was used to assess AP activation in MEE specimens.
- Erythrocyte lysis assays were performed to evaluate complement-mediated hemolysis.
- Levels of complement regulatory proteins, including Factor H (FH) and FH-related proteins (FHRs), were quantified in MEE and serum.
Main Results:
- MEE specimens significantly activated the alternative complement pathway in normal human serum.
- Some MEE samples induced lysis of rabbit erythrocytes, indicating complement system activation.
- FH and FHR proteins were detected in MEE, with FHRs being more abundant than in serum.
- The FH-related protein FHR-5 was identified in MEE.
Conclusions:
- MEE fluid contains components that disrupt the fluid-phase regulation of the alternative complement pathway.
- Increased abundance of FHR proteins in MEE may interfere with FH's regulatory function.
- This dysregulation of the alternative pathway in MEE likely contributes to sustained complement activation and chronic inflammation in OME.
Abstract:
Otitis media with effusion (OME) is a common disease in childhood. It is characterized by chronic inflammation in which the proinflammatory activity of the complement (C) system is one of the underlying factors. The C system becomes strongly activated in the middle ear effusion (MEE) fluid, but the reasons for this are not known. Here we demonstrate by using complement Bb fragment ELISA that MEE specimens strongly activate the alternative C pathway (AP) in normal human serum (NHS). Some of the MEEs were also found to promote lysis of rabbit erythrocytes by NHS. These findings indicated a disturbance in the fluid-phase regulation of the AP in MEE. The main regulator of the AP, factor H (FH), and proteins structurally related to it (FHL-1, FHR-1, -2, -3, and -4) were present in the MEE fluids of OME patients. Relative to serum, the FHR proteins were more abundant in the MEEs. In addition, we detected the recently discovered 65-kDa FH-related protein FHR-5 in the MEE. The FHR proteins share binding sites with FH in the C3d region of C3b. Thus they may compete with FH in binding to C3b and interfere with the regulatory activity of FH. Consequently, a disturbance in AP control in the MEE may lead to an ongoing excessive C activation and inflammation in OME.