The T-cell and antibody responses to a cell surface streptococcal antigen (SA I/II) were investigated in naturally sensitized humans. Serum antibody responses were directed predominantly to the N-terminal (residues 39 to 481) and central (residues 816 to 1213) regions of SA I/II which may be involved in bacterial adhesion to salivary receptors. T-cell responses were also directed predominantly towards the central region. The linear peptide relationship of the immunodominant and minor T-and B-cell as well as adhesion epitopes was mapped within residues 816 to 1213. Immunodominant T-cell and B-cell epitopes were identified within residues 803 to 853, which were separated in linear sequence from the adhesion epitopes (residues 1005 to 1044). Adhesion epitopes overlapped with minor Band T-cell epitopes (residues 1005 to 1054 and 1085 to 1134). An immunodominant promiscuous T-cell epitope (residues 985 to 1004) was adjacent to an adhesion epitope (residues 1005 to 1024). The limited B-cell response to adhesion epitopes is consistent with the success of Streptococcus mutans in colonizing the oral cavity. The strategy of T-cell, adhesion, and B-cell epitope mapping has revealed a general approach for identifying components of subunit vaccines which may focus responses to critical functional determinants. Such epitopes of SA I/II may constitute the components of a subunit vaccine against dental caries.
Attachment ofStreptococcus mutans to the tooth surface involves a cell surface protein with an Mr of 185,000, termed streptococcal antigen (SA) VII. Four overlapping fragments of the gene encoding SA I/IT were amplified by polymerase chain reaction, cloned, and expressed in Escherichia coli. The recombinant polypeptides were assayed for adhesion-binding activity to salivary receptors and for recognition by a panel of monoclonal antibodies (MAbs) raised against SA I/II. Two of the MAbs which are known to prevent colonization of S. mutans in vivo bound the recombinant polypeptide comprising residues 816 to 1161. In vitro adhesion of S. mutans to saliva-coated hydroxyapatite beads was also inhibited specifically by a polypeptide (residues 816 to 1213) encompassing the same region. The evidence from the MAbs preventing colonization of S. mutans and the adherence inhibition assay suggests that an adhesion-binding activity resides within the portion of SA I/I comprising residues 816 to 1213, which is highly conserved among oral streptococcal species.
The spaP gene of Streptococcus mutans serotype c encodes a major cell surface protein, streptococcal antigen (SA) 1/11, with an Mr of 185,000, that is thought to be involved in bacterial adhesion to teeth. Proteins with significant amino acid sequence homology to SA I/II have also been found in S. sobrinus and S. sanguis. The objectives of this study were to investigate the conservation of the spaP gene in the mutans groups of streptococci and to determine whether homologous genes were present in other species of alpha-hemolytic streptococci. DNA extracted from representative strains of 19 streptococcal species was examined by Southern hybridization and partial DNA sequence analysis. A series of five overlapping DNA probes from the spaP gene were amplified by the polymerase chain reaction and used in the Southern hybridizations. The entire gene was found to be well conserved in all strains of S. mutans serotypes c, e, and f investigated. A probe from the 3' region of the gene, which encodes residues 857 to 1207 of the SA I/II protein, hybridized with DNA from a number of mutans streptococci, as well as with DNA from nonmutans alpha-hemolytic streptococci. Conservation within this region was further demonstrated by sequencing gene fragments of two strains of S. intermedius and S. oralis. The results show that some regions of the spaP gene are highly conserved not only in the mutans group of streptococci but also in other nonmutans alpha-hemolytic streptococci. This suggests that a family of cell surface proteins which, by analogy with the 185,000-Mr SA 1/11 of S. mutans, could be involved in bacterial adhesion might exist.
Eosinophilia is a feature common to many invasive helminth infections and eosinophils are often considered to be effector cells in immunity to helminths. This study examined the possible influence of constitutive eosinophilia on the clearance of Schistosoma mansoni infections in mice. Eosinophils from interleukin-5 transgenic mice exhibit normal ultrastructure and function with regard to phagocytosis and killing of bacteria and responses to chemotactic stimuli. IL-5 transgenics and non-transgenic littermates were immunized once or four (hyperimmunization) times with irradiated cercariae of S. mansoni. Animals were challenged percutaneously with unirradiated cercariae one month after their last exposure to irradiated parasites. One month after challenge transgenic animals, whether unimmunized, vaccinated or hypervaccinated, carried significantly more liver-stage parasites than non-transgenic animals. These results suggest that although eosinophils from IL-5 transgenic mice are functional for a number of key parameters, large numbers of eosinophils and/or high levels of IL-5 may in some way impair clearance of S. mansoni. A re-evaluation of the roles of eosinophils and IL-5 in infections with this and other parasites may therefore be warranted.
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