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Clinical and Diagnostic Laboratory Immunology, May 2005, p. 586-592, Vol. 12, No. 5
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.5.586-592.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Analysis of Human Serum Immunoglobulin G against O-Acetyl-Positive and O-Acetyl-Negative Serogroup W135 Meningococcal Capsular Polysaccharide

Department of Applied Immunology and Microbiology, Wyeth Vaccines Research, 401 Middletown Road, Pearl River, New York 10965,¹ Meningococcal Reference Unit, Manchester Medical Microbiology Partnership, Health Protection Agency Northwest, Clinical Sciences Building, Manchester M13 9WZ, United Kingdom²

Received 2 December 2004/ Returned for modification 10 January 2005/ Accepted 28 February 2005

The capsular polysaccharide of Neisseria meningitidis serogroup W135 is expressed in both O-acetyl-positive (OA⁺) and O-acetyl-negative (OA^–) forms. This study investigates the impact of OA status (OA⁺ versus OA^–) on serological measurements of anti-W135 immunoglobulin G (IgG) antibodies in immunized adults. W135-specific serum antibody assignments were made for 28 postimmunization sera from adults by enzyme-linked immunosorbent assay using the meningococcal standard reference serum CDC1992. The established IgG concentration in micrograms per milliliter ([IgG]µg/ml) for CDC1992 against OA⁺ antigen (16.2 µg/ml) was used as a reference to assign a concentration of 10.13 µg/ml IgG against OA^– antigen by cross-standardization. Overall, the IgG assignments for these sera were higher against OA⁺ antigen (geometric mean concentration [GMC] = 7.16 µg/ml) than against OA^– antigen (GMC = 2.84 µg/ml). However, seven sera showed higher specific [IgG]µg/ml values against the OA⁺ antigen than against the OA^– antigen. These sera were also distinguished by the inability of fluid-phase OA^– antigen to compete for antibody binding to OA⁺ solid-phase antigen. Although there was no overall difference in functional activity measured by complement-mediated serum bactericidal assay (SBA) against OA⁺ and OA^– target bacteria (geometric mean titers of 9,642 and 9,045, respectively), three serum specimens showed a large difference in SBA antibody titers against OA⁺ versus OA^– W135 target bacteria, which may reflect different epitope specificities for these sera. Our data indicate that, for some sera, the agreement in anti-OA⁺ versus anti-OA^– W135 IgG assignments is serum specific and does not reflect the functional (killing) activity in vitro.