Microbes bind complement inhibitor factor H via a common site.

Area of Science:

• Immunology
• Microbiology
• Molecular Biology

Background:

• Innate immunity relies on the complement system to eliminate pathogens.
• The alternative pathway of complement is a crucial defense mechanism.
• Factor H (FH) regulates complement activation on host cells.

Purpose of the Study:

• To investigate the mechanism by which diverse microbes bind factor H (FH) for immune evasion.
• To identify the specific binding sites and functional consequences of microbial FH recruitment.

Main Methods:

• Utilized point mutants of FH domains 19-20 (FH19-20) to map microbial binding sites.
• Tested binding of FH19-20 to various microbial proteins and whole microbes (e.g., *Haemophilus influenzae*, *Candida albicans*).
• Assessed the impact of microbial binding on FH's interaction with C3b and complement activation.

Main Results:

• Seven distinct microbial species utilize a common binding region on FH domain 20.
• This microbial binding site overlaps with the heparin-binding site on FH.
• Microbial recruitment of FH enhances FH binding to C3b, forming a tripartite complex and down-regulating complement activation.

Conclusions:

• Microbes have convergently evolved to exploit a conserved FH binding site for immune evasion.
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• Meta_Description='Microbes use a common