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Controlled Clinical Trial
. 2011 Oct;79(10):4146-56.
doi: 10.1128/IAI.05125-11. Epub 2011 Jul 18.

Importance of Antibodies to Lipopolysaccharide in Natural and Vaccine-Induced Serum Bactericidal Activity Against Neisseria Meningitidis Group B

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Free PMC article
Controlled Clinical Trial

Importance of Antibodies to Lipopolysaccharide in Natural and Vaccine-Induced Serum Bactericidal Activity Against Neisseria Meningitidis Group B

Deborah H Schmiel et al. Infect Immun. .
Free PMC article

Abstract

Analysis of the specificity of bactericidal antibodies in normal, convalescent, and postvaccination human sera is important in understanding human immunity to meningococcal infections and can aid in the design of an effective group B vaccine. A collection of human sera, including group C and group B convalescent-phase sera, normal sera with naturally occurring cross-reactive bactericidal activity, and some postvaccination sera, was analyzed to determine the specificity of cross-reactive bactericidal antibodies. Analysis of human sera using a bactericidal antibody depletion assay demonstrated that a significant portion of the bactericidal activity could be removed by purified lipopolysaccharide (LPS). LPS homologous to that expressed on the bactericidal test strain was most effective, but partial depletion by heterologous LPS suggested the presence of antibodies with various degrees of cross-reactivity. Binding of anti-L3,7 LPS bactericidal antibodies was affected by modification of the core structure, suggesting that these functional antibodies recognized epitopes consisting of both core structures and lacto-N-neotetraose (LNnT). When the target strain was grown with 5'-cytidinemonophospho-N-acetylneuraminic acid (CMP-NANA) to increase LPS sialylation, convalescent-phase serum bactericidal titers were decreased by only 2- to 4-fold, and most remaining bactericidal activity was still depleted by LPS. Highly sialylated LPS was ineffective in depleting bactericidal antibodies. We conclude that natural infections caused by strains expressing L3,7 LPS induce persistent, protective bactericidal antibodies and appear to be directed against nonsialylated bacterial epitopes. Additionally, subsets of these bactericidal antibodies are cross-reactive, binding to several different LPS immunotypes, which is a useful characteristic for an effective group B meningococcal vaccine antigen.

Figures

Fig. 1.
Fig. 1.
The bactericidal depletion curves shown were obtained with serum 145-18 and are typical of those obtained with sera from Chilean children having naturally occurring bactericidal antibodies to test strain 8532(B:15:P1.7-2,3:L3,7,8). The antigen concentration is the concentration of antigen that was put in the wells of the plate. A series of concentrations was tested for each antigen. Antigen concentrations were based on protein for NOMV and on dry weight for purified LPS. NOMV contained about 25% LPS.
Fig. 2.
Fig. 2.
The maximum depletion of bactericidal activity obtained with NOMV from the test strain 8532(B:15:P1.7-2,3:L3,7,8), an epidemic outbreak isolate, or an L8 phase variant of the test strain or with purified L1 or L3,7 LPS was determined for sera from 9 Chilean children with bactericidal titers as shown in Table 1. The particular sera assayed are indicated in boldface in Table 1 and are identified by subject number and week/month of bleed. The control serum (17-8) was taken from volunteer 17 at 8 weeks following initial vaccination (2 weeks after the second dose) with a meningococcal group B outer membrane protein vaccine essentially free of LPS (6). BSA, bovine serum albumin.
Fig. 3.
Fig. 3.
A normal human serum (HN026) was tested for specificity of bactericidal activity toward strain 9162(B:15:P1.7-2,3:L3,7) using the bactericidal depletion assay. “WC” indicates whole cells. The concentration is based on protein for NOMV and on dry weight for purified LPS. In the case of the whole cells, a concentration of 100 corresponds to an optical density at 650 nm (OD650) of approximately 1.0 for the suspension of cells applied to the wells, and the other concentrations are 2-fold dilutions of that suspension.
Fig. 4.
Fig. 4.
The representative bactericidal depletion curves shown were obtained with the human convalescent-phase serum HC010 by preincubation with different solid-phase antigens. The test strain was 9162 L3,7. Strain 8532 PorA(−) was a spontaneous mutant of strain 8532, an isolate from the same epidemic clone as 9162 and with the same antigenic profile. The values are the means from duplicate tests, and the error bars show the standard deviations. The antigen concentrations for both NOMV and purified LPS are based on LPS content, using a value of 25% LPS relative to protein for the NOMV.
Fig. 5.
Fig. 5.
Bactericidal activity of convalescent-phase serum HCC010 against strain 9162 L3,7 was depleted by incubation with different solid-phase antigens, including conjugates of sialylated and nonsialylated LNnT. The concentration of NOMV is based on LPS content by KDO assay, and LPS and lacto-N-neotetraose conjugates are based on dry weight.

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