Serum concentration of Hakata antigen, a member of the ficolins, is linked with inhibition of Aerococcus viridans growth.
BACKGROUND
Hakata antigen (Hakata) is a novel serum glycoprotein that consists of collagen- and fibrinogen-like domains, similar to ficolin/p35. Our research suggested that serum Hakata may be a target of a polysaccharide (PSA) produced by Aerococcus viridans.


METHODS
A. viridans was incubated with human plasma and Hakata-depleted plasma to examine Hakata binding and growth inhibition of A. viridans through binding with PSA.


RESULTS
When A. viridans was mixed with human acid citrate dextrose-one (ACD-A) plasma, it pulled down Hakata complexed with mannose-binding lectin (MBL)-associated serine proteases 1 and 2 (MASP-1 and MASP-2). This complex had the potential for C4 deposition. Serum Hakata circulates as Hakata-MASPs complex in the blood and is proteolytically active. By mixing A. viridans with human plasma, we prepared a Hakata-depleted plasma, deficient in Hakata-MASPs complex. This plasma failed to inhibit A. viridans growth plasma, but does not inhibit Staphylococcus aureus, Yersinia enterocolitica and Escherichia coli. However, a decrease of growth inhibition of A. viridans in Hakata-depleted plasma could be restored by adding a Hakata-MASPs complex preparation in a dose-dependent manner. On the other hand, the Hakata-MASPs complex exhibited strong binding to A. viridans, but not to S. aureus, Y. enterocolitica and E. coli.


CONCLUSIONS
The serum concentration of Hakata is linked with growth inhibition of A. viridans upon binding of Hakata via PSA.
D002352:Carrier Proteins / Q000378:metabolism / Q000502:physiology; D003167:Complement Activation; D003181:Complement C4; D006023:Glycoproteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D007109:Immunity; D037102:Lectins / Q000378:metabolism; D050606:Mannose-Binding Protein-Associated Serine Proteases; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D011485:Protein Binding; D012697:Serine Endopeptidases / Q000378:metabolism; D013289:Streptococcaceae / Q000254:growth & development* / Q000276:immunology; D000097604:Ficolins
D002352:Carrier Proteins; D003181:Complement C4; D006023:Glycoproteins; D037102:Lectins; D050606:Mannose-Binding Protein-Associated Serine Proteases; D011135:Polysaccharides, Bacterial; D012697:Serine Endopeptidases; D000097604:Ficolins; C109662:FCN3 protein, human; C084067:MASP1 protein, human; C105296:MASP2 protein, human