Pneumococcal histidine triad proteins are regulated by the Zn2+-dependent repressor AdcR and inhibit complement deposition through the recruitment of complement factor H.

The pneumococcal histidine triad (Pht) proteins are a recently recognized family of surface proteins, comprising 4 members: PhtA, PhtB, PhtD, and PhtE. They are being promoted for inclusion in a multicomponent pneumococcal protein vaccine currently under development, but to date, their biological functions and their relative contributions to pathogenesis have not been clarified. In this study, the involvement of these proteins in pneumococcal virulence was investigated in murine models of sepsis and pneumonia by using defined, nonpolar mutants of the respective genes in Streptococcus pneumoniae D39. In either challenge model, mutagenesis of all 4 genes was required to completely abolish virulence relative to the wild-type, suggesting significant functional redundancy among Pht proteins. The in vivo expression of pht genes was significantly up-regulated in the nasopharynx and lungs compared with blood. We provide unequivocal molecular evidence for Zn(2+)-dependent, AdcR-mediated, regulation of pht gene expression by real-time reverse transcriptase-polymerase chain reaction, Western blotting, and electrophoretic mobility-shift assays. We also present the first direct evidence for the biological function of this protein family by demonstrating that Pht proteins are required for inhibition of complement deposition on the pneumococcal surface through the recruitment of complement factor H.

c-di-GMP is an effective immunomodulator and vaccine adjuvant against pneumococcal infection.

Cyclic diguanylate (c-di-GMP) is a unique bacterial intracellular signaling molecule capable of stimulating enhanced protective innate immunity against various bacterial infections. The effects of intranasal pretreatment with c-di-GMP, or intraperitoneal coadministration of c-di-GMP with the pneumolysin toxoid (PdB) or pneumococcal surface protein A (PspA) before pneumococcal challenge, were investigated in mice. We found that c-di-GMP had no significant direct short-term effect on the growth rate of Streptococcus pneumoniae either in vitro or in vivo. However, intranasal pretreatment of mice with c-di-GMP resulted in a significant decrease in bacterial load in lungs and blood after serotypes 2 and 3 challenge, and a significant decrease in lung titers after serotype 4 challenge. Potential cellular mediators of these enhanced protective responses were identified in lungs and draining lymph nodes. Intraperitoneal coadministration of c-di-GMP with PdB or PspA before challenge resulted in significantly higher antigen-specific antibody titers and increased survival of mice, compared to that obtained with alum adjuvant. These findings demonstrate that local or systemic c-di-GMP administration stimulates innate and adaptive immunity against invasive pneumococcal disease. We propose that c-di-GMP can be used as an effective broad spectrum immunomodulator and vaccine adjuvant to prevent infectious diseases.

Development of a vaccine against invasive pneumococcal disease based on combinations of virulence proteins of Streptococcus pneumoniae.

Current global efforts are focused on exploring alternative pneumococcal vaccine strategies, aimed at addressing the shortcomings of existing formulations, without compromising efficacy. One such strategy involves the use of one or more pneumococcal protein antigens common to all serotypes, to provide cheap, non-serotype-dependent protection. In this study, we evaluated the protective efficacy of immunization of mice with PdB (a pneumolysin toxoid), PspA, PspC (CbpA), PhtB, and PhtE in an invasive-disease model. The antigens were administered in alum adjuvant, either alone or in various combinations. Protection against intraperitoneal challenge with virulent type 2 and 6A strains was assessed in two murine strains. Our findings show that in some situations, different individual proteins gave the best (and worst) protection. However, in many cases, a synergistic/additive effect was seen by using multiple proteins even where the individual proteins showed little value by themselves. For instance, the median survival times for mice immunized with combinations of PdB and PspA, PdB and PspC, or PspA and PspC were significantly longer than those for mice immunized with any of the single antigens. To date, the combination of PdB, PspA, and PspC offers the best protection.

A recombinant probiotic for treatment and prevention of cholera.

BACKGROUND & AIMS: We have developed a therapeutic strategy based on molecular mimicry of host receptors for bacterial toxins on the surface of harmless gut bacteria. In the present study, this has been applied to the development of a recombinant probiotic for treatment and prevention of cholera, caused by Vibrio cholerae. METHODS: We expressed glycosyltransferase genes from Neisseria gonorrhoeae and Campylobacter jejuni in a harmless Escherichia coli strain, resulting in production of a chimeric lipopolysaccharide terminating in a mimic of the ganglioside GM(1). RESULTS: The recombinant bacterium was capable of binding cholera toxin, a sine qua non of virulence, with high avidity; when tested with purified cholera toxin, it was capable of adsorbing >5% of its own weight of toxin in vitro. Administration of the GM(1)-expressing probiotic also protected infant mice against challenge with virulent V cholerae, even when treatment was delayed until after establishment of infection. When treatment commenced 1 hour after challenge, 12 of 12 mice given the probiotic survived, compared with only 1 of 12 for control mice (P < .00001). CONCLUSIONS: Toxin-binding probiotics such as that described here have considerable potential for prophylaxis and treatment of cholera in humans.