Murine Immune Response toNeisseria meningitidisGroup C Capsular Polysaccharide: Analysis of Monoclonal Antibodies Generated in Response to a Thymus-Independent Antigen and a Thymus-Dependent Toxoid Conjugate Vaccine

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Abstract
Antibody (Ab) responses to polysaccharides (PSs) such asNeisseria meningitidisgroup C PS (MCPS) are characterized as being thymus independent (TI) and are restricted with regard to clonotype and isotype expression. PS conjugated to proteins, e.g., MCPS coupled to tetanus toxoid (MCPS-TT), elicits a thymus-dependent (TD) response. In order to understand the influence of the form of a vaccine (TI versus TD) on the Ab repertoire, we generated monoclonal antibody (MAb) panels from mice immunized and boosted with MCPS or MCPS-TT in different ways. The panels of MAbs were examined for isotype, fine specificity, affinity, and VHgene family usage. The use of MCPS-TT resulted in a shift in the isotype from immunoglobulin M (IgM) and IgG3 elicited in response to the MCPS to primarily IgG1. This isotype shift was accompanied by a change in the fine specificity of the response to the conjugate compared to that of PS. New fine specificities and increased affinity were observed in response to the TD antigen (Ag). Dot blot and Northern analyses of MCPS MAbs revealed that VHgene family usage is dominated by VHJ558, used by 23 of 39 MAbs. VH3609 was seen in three MAbs of restricted fine specificity. VHQ52, VH7183, and VHVGAM3-8 were seen in more than one MAb across these panels, while VH10 and VHX24 were detected only once in response to the TI-2 Ag. All MAbs in the panels utilized kappa light chains, and all functional Jκgenes were expressed.

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