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Infection and Immunity, October 2002, p. 5589-5595, Vol. 70, No. 10
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.10.5589-5595.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Enhanced Immunogenicity of Pneumococcal Surface Adhesin A by Genetic Fusion to Cytokines and Evaluation of Protective Immunity in Mice

Institute of Pathology,¹ Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland, Ohio 44106-4943²

Received 1 April 2002/ Returned for modification 14 May 2002/ Accepted 1 July 2002

Immunization of mice with pneumococcal surface adhesin A (PsaA) emulsified in complete Freund's adjuvant (CFA) provides protection against systemic infection with Streptococcus pneumoniae. Because the use of CFA is not acceptable in humans, we sought to develop alternative means of enhancing the immunogenicity of protein antigens of potential use in pneumococcal vaccines. We designed a series of genetic constructs in which coding sequences for PsaA were linked to sequences encoding either murine interleukin-2 (mIL-2), mIL-4, or two copies of an immunostimulatory nonapeptide derived from mIL-1ß. The PsaA-cytokine constructs were cloned and expressed in Escherichia coli. Mice immunized twice with PsaA-IL-2, or PsaA-IL-4 responded with PsaA-specific antibody production comparable in magnitude to that of mice primed with PsaA in CFA and boosted with PsaA in incomplete Freund's adjuvant (PsaA-Adj). Antibodies elicited by PsaA-Adj were predominantly of the immunoglobulin G1 (IgG1) subclass, while PsaA-IL-2 and PsaA-IL-4 elicited substantial amounts of IgG2a in addition to IgG1. Mice immunized with PsaA-Adj or PsaA-IL-4 were partially protected against intraperitoneal challenge with virulent S. pneumoniae (30% overall survival beyond 15 days postchallenge). Mice immunized with PsaA and no adjuvant or PsaA-IL-2 exhibited 0 or 5% survival rates, respectively, following challenge. In contrast, mice immunized twice with capsular polysaccharide were 100% protected. The modest levels of protection seen in mice immunized with PsaA and its more immunogenic derivatives may be explained in part by the relative inaccessibility of antibody to PsaA on the surface of encapsulated S. pneumoniae.

Editor: J. D. Clements

This article has been cited by other articles:

• Gor, D. O., Ding, X., Briles, D. E., Jacobs, M. R., Greenspan, N. S. (2005). Relationship between Surface Accessibility for PpmA, PsaA, and PspA and Antibody-Mediated Immunity to Systemic Infection by Streptococcus pneumoniae. Infect. Immun. 73: 1304-1312 [Abstract] [Full Text]