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Infect. Immun. doi:10.1128/IAI.00837-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

L-ficolin/Mannose-Binding Lectin-Associated Serine Protease Complexes Bind to Group B Streptococci Largely through N-Acetylneuraminic Acid of Capsular Polysaccharide, and Activate the Complement Pathway

Division of Microbiology, Joshi-Eiyoh (Kagawa Nutrition) University, Sakado, Japan, Department of Infectious Diseases, St. Jude Children's Research Hospital, Memphis, Department of Pediatrics, Children's Hospital and Regional Medical Center, University of Washington, Seattle, Department of Pediatrics, University of Utah Health Sciences Center, Salt Lake City, Department of Applied Biochemistry, Tokai University, Hiratsuka, Japan, and Department of Immunology, Fukushima Medical University, Fukushima Japan

^* To whom correspondence should be addressed. Email: tshinji{at}eiyo.ac.jp.

	Abstract

Group B streptococci (GBS) are the most common cause of neonatal sepsis and meningitis. Most infants who are colonized with GBS at birth do not develop invasive disease, although many of these uninfected infants lack protective levels of capsular polysaccharide (CPS)-specific antibody. The lectin pathway of complement is a potential mechanism for initiating opsonization of GBS with CPS-specific antibody-deficient serum. In these studies, we determined whether mannose-binding lectin (MBL)/MBL-associated serine protease (MASP) complexes and L-ficolin/MASP complexes bind to different strains of GBS to activate the lectin pathway, and identified the molecules recognized by lectins on the GBS surface. In the present study, MBL did not bind to any GBS examined, whereas L-ficolin bound to GBS cells of many serotypes. L-ficolin binding to GBS cells correlated with CPS content in serotypes Ib, III (restriction digestion pattern types III-2 and III-3), and V, but not with group B-specific polysaccharide (GBPS) content nor with lipoteichoic acid (LTA) content. L-ficolin bound to purified CPS and GBPS in a concentration-dependent manner, but not to purified LTA. All strains to which L-ficolin/MASP complexes had bound consumed C4. When N-acetylneuraminic acid (NeuNAc) was selectively removed from GBS cells by treatment with neuraminidase, the reduction in L-ficolin binding was correlated with the amount of NeuNAc removed. Additionally, L-ficolin was able to bind to wild type strains, but only weakly to unencapsulated mutants and a mutant strain in which the CPS lacks NeuNAc. We conclude that L-ficolin/MASP complexes bind to GBS largely through an interaction with NeuNAc of CPS.