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Heteroligomeric forms of codon 54 mannose binding lectin (MBL) in circulation demonstrate reduced in vitro function
M M Dean1, S Heatley, R M Minchinton
1Co-operative Research Centre for Vaccine Technology, at the Australian Red Cross Blood Service, Adelaide St, Brisbane, Queensland, Australia 4000. mdean@arcbs.redcross.org.au
Molecular Immunology
|August 16, 2005
Summary
Mannose-binding lectin (MBL) structure varies by genotype, impacting innate immunity. High molecular weight MBL in wild-type individuals correlates with stronger immune responses, while other genotypes show reduced activity.
Area of Science:
- Immunology
- Biochemistry
- Genetics
Background:
- Mannose-binding lectin (MBL) is a key pattern recognition molecule in innate immunity.
- It is a liver-derived plasma protein that initiates the lectin pathway of complement cascade.
- MBL binds to carbohydrate structures on pathogens, marking them for destruction.
Purpose of the Study:
- To investigate native, oligomeric forms of human MBL in plasma.
- To correlate MBL molecular weight species with mannan binding activity and C4 deposition across different genotypes.
- To propose a model for C4 deposition based on MBL structure and MASP binding.
Main Methods:
- Analysis of plasma from healthy blood donors with varying MBL genotypes.
- Determination of MBL oligomeric forms and molecular weights.
- In vitro assays measuring mannan binding activity and C4 deposition.
Main Results:
- Wild-type (A/A) individuals predominantly exhibit high molecular weight MBL, correlating with high mannan binding and C4 deposition.
- A/C individuals show predominantly low molecular weight MBL with reduced binding and deposition activity.
- A/D individuals display mixed molecular weights, with reduced activity often linked to the LX promoter.
- A/B individuals exhibit significant variation in MBL levels, binding activity, and C4 deposition.
Conclusions:
- MBL genotype significantly influences its oligomeric structure and functional capacity.
- The abundance of specific MBL molecular weight forms directly impacts mannan binding and complement activation (C4 deposition).
- A model is proposed for C4 deposition, highlighting the role of MASP binding to different MBL structures.