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Murine immune response to the Neisseria meningitidis group C capsular polysaccharide. II. Specificity
1Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, MD 20892.
Abstract:
As a means of further understanding the regulation of diversity and the development of protective immunity to the Neisseria meningitidis group C capsular polysaccharide (MCPS), we have generated and characterized, in detail, a panel of mAb against MCPS, a homopolymer of alpha(2----9)-sialic acid. Whereas the serum response to MCPS is restricted to the IgM and IgG3 isotypes, the panel of mAb includes, in addition, both IgG1 and IgG2b. Among 15 mAb of four isotypes, seven different specificities were observed based on direct binding in a fluorescence ELISA and precipitation in gel. Although all the mAb were derived from mice immunized with bacteria encapsulated with the native MCPS (strain C11), only 7 of 15 reacted with MCPS alone. Seven of 15 reacted with a natural O-acetyl-negative variant (OAc-, strain MC19) polysaccharide as well as with MCPS. Five of these reacted as much as 3 logs better with OAc- than MCPS and the other two reacted better with MCPS than OAc-. One mAb appeared to be alpha(2----9)-linkage specific as it reacted not only with MCPS and OAc-, but also with the capsular polysaccharide of Escherichia coli K92, a polymer of sialic acid linked alternately alpha(2----8) and alpha(2----9). None of the mAb reacted with the capsular polysaccharide of E. coli K1, a homopolymer of alpha(2----8)-sialic acid. In general, there was a good correlation between the ability to precipitate Ag in gel and to agglutinate bacteria; however, 3 of 15 mAb, all IgG3, did not conform to this rule in that they precipitated Ag but did not agglutinate bacteria of the relevant capsular specificity. Antibodies of both IgM and IgG isotypes and of both major specificities, MCPS-specific and those binding MCPS and OAc-, were bactericidal for strain C11, whereas only those reactive with OAc- were able to kill strain MC19.
Insights
Researchers developed monoclonal antibodies (mAbs) against Neisseria meningitidis group C capsular polysaccharide (MCPS). These antibodies revealed diverse specificities and provided insights into protective immunity against meningococcal disease.
Area of Science:
- Immunology
- Microbiology
- Bacteriology
Background:
- Understanding immunity to Neisseria meningitidis group C is crucial for disease prevention.
- The group C capsular polysaccharide (MCPS) is a key target for protective immune responses.
- Previous studies indicated restricted antibody isotype responses to MCPS.
Purpose of the Study:
- To generate and characterize a comprehensive panel of monoclonal antibodies (mAbs) against MCPS.
- To investigate the diversity of antibody specificities targeting MCPS and related structures.
- To elucidate the role of different antibody isotypes and specificities in protective immunity and bactericidal activity.
Main Methods:
- Generation of a panel of 15 mAbs from mice immunized with Neisseria meningitidis group C (strain C11).
- Characterization of mAb specificities using fluorescence ELISA and gel precipitation assays.
- Assessment of antibody reactivity against native MCPS, an O-acetyl-negative variant (OAc-), and other bacterial polysaccharides (E. coli K92, E. coli K1).
Main Results:
- Seven distinct mAb specificities were identified among the 15 mAbs.
- Antibodies exhibited varying reactivity to MCPS and the OAc- variant, with some showing significantly higher affinity for OAc-.
- One mAb demonstrated specificity for alpha(2----9) linkages, reacting with MCPS, OAc-, and E. coli K92 polysaccharides.
- Antibodies of multiple isotypes (IgM, IgG1, IgG2b, IgG3) were generated, expanding beyond the typical serum response.
- Bactericidal activity was observed for antibodies targeting both MCPS and OAc-, with OAc--reactive antibodies being essential for killing strain MC19.
Conclusions:
- The study successfully generated a diverse panel of mAbs against MCPS, revealing broader specificity than previously understood.
- These mAbs provide valuable tools for dissecting the immune response to MCPS and understanding protective immunity.
- The findings highlight the importance of antibody recognition of O-acetylation and specific sialic acid linkages for effective bactericidal activity against Neisseria meningitidis.