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Role of ficolin-A and lectin complement pathway in the innate defense against pathogenic Aspergillus species
Stefan Bidula1, Hany Kenawy, Youssif M Ali
1Norwich Medical School, University of East Anglia, Norwich, United Kingdom.
Abstract:
Aspergillus species are saprophytic molds causing life-threatening invasive fungal infections in the immunocompromised host. Innate immune recognition, in particular, the mechanisms of opsonization and complement activation, has been reported to be an integral part of the defense against fungi. We have shown that the complement component ficolin-A significantly binds to Aspergillus conidia and hyphae in a concentration-dependent manner and was inhibited by N-acetylglucosamine and N-acetylgalactosamine. Calcium-independent binding to Aspergillus fumigatus and A. terreus was observed, but binding to A. flavus and A. niger was calcium dependent. Ficolin-A binding to conidia was increased under low-pH conditions, and opsonization led to enhanced binding of conidia to A549 airway epithelial cells. In investigations of the lectin pathway of complement activation, ficolin-A-opsonized conidia did not lead to lectin pathway-specific C4 deposition. In contrast, the collectin mannose binding lectin C (MBL-C) but not MBL-A led to efficient lectin pathway activation on A. fumigatus in the absence of ficolin-A. In addition, ficolin-A opsonization led to a modulation of the proinflammatory cytokine interleukin-8. We conclude that ficolin-A may play an important role in the innate defense against Aspergillus by opsonizing conidia, immobilizing this fungus through enhanced adherence to epithelial cells and modulation of inflammation. However, it appears that other immune pattern recognition molecules, i.e., those of the collectin MBL-C, are involved in the Aspergillus-lectin complement pathway activation rather than ficolin-A.
Insights
Ficolin-A binds Aspergillus fungi, enhancing their adherence to airway cells and modulating inflammation. However, mannose-binding lectin C, not ficolin-A, activates the Aspergillus-lectin complement pathway.
Area of Science:
- Immunology
- Mycology
- Infectious Diseases
Background:
- Aspergillus species cause severe infections in immunocompromised individuals.
- Innate immune recognition, including opsonization and complement activation, is crucial for antifungal defense.
- Ficolin-A is a complement component involved in innate immunity.
Purpose of the Study:
- To investigate the role of ficolin-A in the innate immune response to Aspergillus species.
- To determine ficolin-A's binding characteristics to Aspergillus conidia and hyphae.
- To assess ficolin-A's impact on complement activation and inflammatory responses.
Main Methods:
- Assessed ficolin-A binding to Aspergillus species (A. fumigatus, A. terreus, A. flavus, A. niger) under various conditions (pH, calcium dependency).
- Evaluated ficolin-A opsonization's effect on conidia adherence to A549 airway epithelial cells.
- Investigated lectin pathway complement activation (C4 deposition) using ficolin-A and mannose-binding lectin C (MBL-C) or A (MBL-A).
- Measured modulation of interleukin-8 (IL-8) levels following ficolin-A opsonization.
Main Results:
- Ficolin-A demonstrated concentration-dependent binding to Aspergillus conidia and hyphae, inhibited by specific sugars.
- Binding was calcium-independent for A. fumigatus and A. terreus, but calcium-dependent for A. flavus and A. niger.
- Ficolin-A opsonization increased conidia adherence to epithelial cells and modulated IL-8 levels.
- Ficolin-A did not induce lectin pathway-specific C4 deposition; MBL-C, but not MBL-A, efficiently activated this pathway on A. fumigatus.
Conclusions:
- Ficolin-A contributes to innate defense against Aspergillus by enhancing fungal adherence to epithelial cells and modulating inflammation.
- Ficolin-A may immobilize Aspergillus through increased epithelial cell binding.
- MBL-C, rather than ficolin-A, appears to be the primary activator of the Aspergillus-lectin complement pathway.
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