Defining antibody targets in Streptococcus oralis infection

Abstract

Immunoblotting of sera from 12 neutropenic patients with Streptococcus oralis septicemia and 18 patients with endocarditis due to viridans group streptococci revealed immunodominant S. oralis antigens at 85 and 180 kDa. The former cross-reacted with a mouse monoclonal antibody to hsp90. The latter was identified by sequencing positive clones obtained by screening a genomic expression library of S. oralis with pooled sera from patients who had been infected with S. oralis. Antibody eluted from one of these clones reacted with the 180-kDa antigen of S. oralis. Southern blotting confirmed the origin of the clone from S. oralis. The derived amino acid sequence showed 76.2% homology with the PAc protein precursor of Streptococcus mutans and 73.8% homology with the SpaA protein precursor of Streptococcus sobrinus. Epitope mapping of the derived amino acid sequence with sera from patients with viridans group streptococcal endocarditis delineated nine epitopes. Peptides 1 (TMYPNRQPGSGWDSS) and 2 (WYSLNGKIRAVDVPK), representing two of these epitopes, and peptide 3 (YEVEKPLEPAPVAPS), representing the repeat proline region, were synthesized. These three peptides were used to screen a phage antibody display library derived from a patient who had recovered from S. oralis infection. Two of the human recombinant antibodies produced (SORAL 3 and SORAL 4 against peptide 3) and a human recombinant antibody (B3.7) against the conserved epitope (LKVIRK) of hsp90 gave statistically significant protection, compared with control groups, in a mouse model of lethal S. oralis infection.

Biochemical and genetic characterization of serologically untypable Streptococcus mutans strains isolated from patients with bacteremia

“…Antibodies to surface PA were elevated greatly in patients with S. mutans infective endocarditis (24). Antibodies against similar surface proteins were reported in S. sobrinus (25), and S. oralis (26). In S. mutans, including the untypable strains used here, PA gives a common immunological speci®city and is highly immunogenic.…”

Structure, function and immunogenicity of streptococcal antigen I/II polypeptides

“…Antibodies to antigen I/II polypeptides are present in sera of patients with streptococcal endocarditis (Burnie et al, 1996). An increased number of antigen I/II B-cell epitopes were identified in these patients, with a major B-cell epitope present as part of the exclusively T-cell epitope in naturally sensitized humans (Fig.…”

Identification of ABC transporters in vancomycin-resistant Enterococcus faecium as potential targets for antibody therapy

“…A humoral response which blocks ABC transporter function by targeting shared epitopes common to multiple transporters would simultaneously interfere with numerous processes key to the survival of the bacteria and its ability to function as a pathogen. It would explain the widespread immunodominance of these molecules in Gram-positive infections [14,15,33,34] and act as a potent method by which a single antibody could produce a therapeutic e¡ect. The potential therapeutic activity of such antibodies is now under further investigation.…”

“…IgM and IgG were assayed separately, except for the control Group 1 where they were combined. Blots were analysed as described previously [14,15]: antibody was recorded as present if the intensity of the bound antibody was s 50 mm by re£ectance densitometry (Chromoscan 3; Joyce Loebl) ; where multiple sequential sera were tested, titres were reported as constant if the variation in height of the trace remained within 5 mm whereas a rising antibody response was recorded if there was an increase of at least 30 mm.…”