Monoclonal antibodies that recognize a common pneumococcal protein with similarities to streptococcal group A surface glyceraldehyde-3-phosphate dehydrogenase.

Monoclonal antibodies (MAbs) against clinical isolates of Streptococcus pneumoniae were produced in a search for common pneumococcal proteins. One of the fusions generated two MAbs, 174,B-8 (immunoglobulin G2a) and 177,D-8 (immunoglobulin G1), which by Western blotting (immunoblotting) stained with a main band of 40 kDa found in all isolates of S. pneumoniae examined. Cross-reactivity studies with streptococci other than pneumococci revealed very weak or moderate reactions with the MAbs. The 40-kDa protein was isolated by immunoaffinity chromatography and subsequent preparative Western blotting. N-terminal amino acid sequencing showed 90% amino acid sequence homology with a surface-located glyceraldehyde-3-phosphate dehydrogenase from Streptococcus pyogenes. This protein has also been reported to exhibit binding to mammalian proteins such as fibronectin, which may serve as host receptors. The epitopes for MAbs 174,B-8 and 177,D-8 reacting with the pneumococcal analog were not accessible to antibody binding in live bacteria but were exposed after heat killing. The MAbs showed negligible cross-reactions with S. pyogenes.