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Streptococcus pneumoniae is a microorganism that frequently causes serious infections in children, the elderly, and immunocompromised patients. We studied whether the specific intracellular adhesion molecule-grabbing nonintegrin R1 (Sign-R1) receptor, involved in the uptake of capsular polysaccharides (caps-PS) by antigen-presenting cells, is necessary for the antibody response to pneumococcal caps-PS and phosphorylcholine (PC). The antibody response to caps-PS and PC was evaluated after vaccination with soluble caps-PS (Pneumovax) and after vaccination with heat-killed S. pneumoniae. The role of Sign-R1 was investigated by using Sign-R1 knockout mice and anti-Sign-R1 monoclonal antibodies. The immunoglobulin M (IgM) and IgG antibody response to PC and caps-PS (serotypes 3 and 14) was not affected by anti-Sign-R1 monoclonal antibodies. The IgM antibody response in Sign-R1 knockout mice was comparable to the antibody response in wild-type mice. The IgG antibody response to serotype 3, but not to serotype 14, tended to be lower in Sign-R1 knockout mice compared to wild-type mice. In conclusion, we found that Sign-R1 is not involved in the IgM antibody production to PC and caps-PS serotype 3 or 14 and the IgG immune response to PC and caps-PS serotype 14. There is no direct relation between capture and uptake of caps-PS serotype 14 by Sign-R1 and the initiation of the anti-caps-PS antibody production in mice.

Intranasal challenge of C57BL/6 mice with Streptococcus pneumoniae serotypes 6B, 14, and 23F produced colonization of the middle ear and NP. Intranasal vaccination with ethanol-killed nonencapsulated cells with adjuvant protected both sites. Of four nontoxic adjuvants tested, the cholera toxin B subunit was most effective and least nonspecifically protective.

The development of a vaccine against Streptococcus pneumoniae has been complicated by the existence of at least 90 antigenically distinct capsular serotypes. Common protein-based vaccines could represent the best strategy to prevent pneumococcal infections, regardless of serotype. In the present study, the immunoscreening of an S. pneumoniae genomic library allowed the identification of a novel immune protein target, BVH-3. We demonstrate that immunization of mice with BVH-3 elicits protective immunity against experimental sepsis and pneumonia. Sequence analysis revealed that the bvh-3 gene is highly conserved within the species. Since the BVH-3 protein shows homology at its amino-terminal end with other pneumococcal proteins, it was of interest to determine if protection was due to the homologous or to the protein-specific regions. Immunoprotection studies using recombinant BVH-3 and BVH-3-related protein fragments as antigens allowed the localization of surface-exposed and protective epitopes at the protein-specific carboxyl termini, thus establishing that BVH-3 is distinct from other previously reported protective protein antigens. Immunization with a chimeric protein comprising the carboxyl-terminal regions of BVH-3 and of a BVH-3-related protein improved the protection by targeting two surface pneumococcal components. Thus, BVH-3 and the chimeric protein hold strong promise as vaccine components to control pneumococcal disease.

CBA/J mice immunized with pneumococcal 23F-CRM(197) vaccine produce significantly lower titers of 23F-specific antibodies and fewer 23F-specific antibody-secreting cells (ASC) than did BALB/c or (CBA/J x BALB/c)F(1) (CCBAF(1)) mice. The reduced 23F-specific titers of CBA/J versus BALB/c or CCBAF(1) mice are presumably related to lower frequencies of 23F-specific ASC influenced by genetic variation.

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-1beta. 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.