Abstract
Monoclonal antibodies (MAbs) against a nonencapsulated strain (R36A) of Streptococcus pneumoniae were produced to aid in a search for antigens common to this species. By Western immunoblot analysis, a species-specific 37-kilodalton (kDa) protein was found in lysates of 24 different encapsulated strains of S. pneumoniae. Monoclonal antibodies against the 37-kDa antigen did not react with 55 heterologous strains representing 19 genera and 36 species of bacteria that can also cause acute lower respiratory tract disease. Immunogold staining suggests that the antigen is synthesized inside the pneumococcal cell. However, MAbs to the 37-kDa antigen bound whole cells in the enzyme-linked immunosorbent assay and the indirect immunofluorescence assay. Antibody-binding epitopes of the antigen are probably exposed on the outer surface of the pneumococcus cell wall. The effectiveness of the 37-kDa antigen as a useful diagnostic marker is under study.