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Published on: December 23, 2016
Immunogenicity of synthetic peptides derived from the sequences of a Streptococcus mutans cell surface antigen in
T Lehner1, P Walker, L A Bergmeier
1Department of Immunology, United Medical School of Guy's Hospital, London, UK.
Abstract:
The immunogenicity and antigenicity of synthetic peptides (SP) derived from the sequences of a cell surface Ag of Streptococcus mutans were investigated in macaque monkeys. Immunization with the free peptides of 11, 17, and 21 residues failed to elicit serum antibodies or T cell responses. However, immunization with the SP17 and SP21 linked to tetanus toxoid (TT) as a carrier elicited serum antibodies and proliferative responses of lymphocytes, not only to the SP but also to the native streptococcal Ag. In vivo recall of SP-TT immunized monkeys with suboptimal doses of the native streptococcal Ag resulted in a significant increase in antibodies, both to the SP and the streptococcal Ag, confirming that the SP shares antigenic epitopes with the native Ag. B and T cell epitopes were then determined and a B cell epitope was found in residues 8-13, whereas an overlapping T cell epitope was located in residues 7-15. The T cell epitope has an amino-terminal leucine and carboxy-terminal glycine and alanine added to residues 8-13 of the B cell epitope. In spite of the B and T cell epitopes being expressed in SP17 (residues 1-15), the monomer failed to induce serum antibodies without a carrier. However, immunization with a dimer of SP17 elicited both serum antibodies and proliferative responses of lymphocytes without a carrier. The results suggest that the monomeric SP17 is not immunogenic and needs to be dimerised in order to elicit antibodies and T cell responses, both to the SP and to the streptococcal Ag.
Insights
Synthetic peptides from Streptococcus mutans require a carrier protein to elicit immune responses. Dimerizing these peptides enhances immunogenicity, inducing antibodies and T cell responses against both the peptide and native antigens.
Area of Science:
- Immunology
- Microbiology
- Vaccine Development
Background:
- Streptococcus mutans is a key pathogen in dental caries.
- Cell surface antigens of S. mutans are targets for immune-mediated protection.
- Synthetic peptides (SP) derived from these antigens are potential vaccine candidates.
Purpose of the Study:
- To investigate the immunogenicity and antigenicity of synthetic peptides (SP) from S. mutans.
- To identify B and T cell epitopes within the SP.
- To determine the requirements for eliciting effective immune responses against S. mutans antigens.
Main Methods:
- Immunization of macaque monkeys with free SP, SP conjugated to tetanus toxoid (TT), and dimeric SP.
- Assessment of serum antibodies and lymphocyte proliferation.
- In vivo recall experiments with native streptococcal antigen.
- Epitope mapping to identify specific B and T cell recognition sites.
Main Results:
- Free SP failed to induce immune responses.
- SP conjugated to TT elicited antibodies and T cell responses to both SP and native S. mutans antigen.
- A B cell epitope was located at residues 8-13 and an overlapping T cell epitope at residues 7-15.
- Monomeric SP17 was not immunogenic, but dimeric SP17 elicited antibodies and lymphocyte proliferation without a carrier.
Conclusions:
- Synthetic peptides from S. mutans require conjugation to a carrier protein or dimerization to become immunogenic.
- Identified B and T cell epitopes provide insights for designing subunit vaccines.
- Dimerization is a viable strategy to enhance the immunogenicity of synthetic peptide antigens.
