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Clinical and Diagnostic Laboratory Immunology, August 2005, p. 930-934, Vol. 12, No. 8
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.8.930-934.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Naturally Acquired Antibodies against Four Enterococcus faecalis Capsular Polysaccharides in Healthy Human Sera

Markus Hufnagel,1,2 Andrea Kropec,1 Christian Theilacker,1,4 and Johannes Huebner1,3,4*

Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts,1 University Children's Hospital, University Hospital Schleswig-Holstein, Campus Kiel, Germany,2 Division of Infectious Diseases, Children's Hospital, Harvard Medical School, Boston, Massachusetts,3 Division of Infectious Diseases, Department of Medicine II, University Hospital Freiburg, Germany4

Received 11 February 2005/ Returned for modification 22 March 2005/ Accepted 27 May 2005

Healthy human sera (HHS) contain naturally acquired enterococcal antibodies which promote neutrophil-mediated killing. The target antigens remain unknown. The present study used a capsular polysaccharide (CPS)-enzyme-linked immunosorbent assay (ELISA) to investigate whether the HHS antibodies of 12 healthy donors bound to the CPS of four E. faecalis serotypes (CPS-A to CPS-D) and then employed an opsonic-killing assay to determine if these antibodies mediated phagocyte-dependent killing. All HHS contained immunoglobulin G (IgG) and IgM antibodies directed against capsular polysaccharides of the four serotypes. Absorption of the sera with homologous and heterologous strains showed a majority of antibodies to be cross-reactive among the prototype strains. The susceptibility of the four prototype strains to opsonic killing varied. Opsonic killing of CPS-A and CPS-B strains was significantly higher than killing of CPS-C and CPS-D strains. Absorption studies revealed that the opsonic killing of HHS was only partially type specific, with cross-reactivity between CPS-A and CPS-B strains and between CPS-C and CPS-D strains. These data indicate that healthy individuals possess opsonic antibodies specific for CPS-A and CPS-B but only low titers of opsonic antibodies against CPS-C and CPS-D. Titers of opsonic antibodies did not correlate with antibody titers measured by ELISA. Whether this lack of correlation is due to the low frequency of opsonic antibodies or to increased resistance to the opsonophagocytic killing of some serotypes remains to be determined.

* Corresponding author. Mailing address: Division of Infectious Diseases, Department of Medicine, University Hospital Freiburg, Hugstetter Str. 55, 79106 Freiburg, Germany. Phone: 49-761-270-1828. Fax: 49-761-270-1820. E-mail: johannes.huebner{at}uniklinik-freiburg.de.

Clinical and Diagnostic Laboratory Immunology, August 2005, p. 930-934, Vol. 12, No. 8
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.8.930-934.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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