Immune Reactivity of Four Monoclonal and Two Polyclonal Antibodies Raised Against Recombinant Pneumococcal Surface Adhesin A

Abstract

In this study four monoclonal antibodies (MAbs) and two polyclonal antisera were raised against pneumococcal surface adhesion A (psaA), a 37 kDa cell wall protein, and were characterized. The MAbs were purified, isotyped, and epitope mapped with peptide microarrays. All monoclonals and polyclonals underwent testing in immunodot blot, Western blot, and ELISA assays to assess their specificity. All monoclonal antibodies belonged to isotype IgG1 κ. Peptide microarray mapping identified two likely epitopes, which could not be confirmed using synthetic peptides of the identified amino acid sequence. All four MAbs detected the 53 pneumococcal serotypes tested in the immunodot blot and only reacted with Streptococcus pseudopneumoniae in cross-reactivity studies by Western blot. The polyclonal antisera also recognized all tested pneumococcal serotypes and cross-reacted with S. pseudopneumoniae and Streptococcus oralis by Western blot. The MAbs cross-reacted with S. pseudopneumoniae in the ELISA. Both polyclonal antisera cross-reacted with all isolates tested in the ELISA. These antisera should be suitable to establish a diagnostic ELISA platform for pneumococcal antigen detection with polyclonal antisera as the capture antibody. The specificity of the four MAbs appears to be high as they only recognized S. pneumoniae and S. pseudopneumoniae. However, further testing of closely related streptococcal species is necessary to confirm this finding.