Binding of Streptococcus mutans SR protein to human monocytes: production of tumor necrosis factor, interleukin 1, and interleukin 6
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M Soell1, F Holveck, M Schöller
1Faculté de Pharmacie, Unité 392, Institut National de la Santé et de la Recherche Médicale, Illkirch, France.
Abstract:
To examine the possible implication of protein SR, an I/II-related antigen from Streptococcus mutans OMZ 175 (serotype f), in inflammatory reactions, we tested the immunomodulatory effects of protein SR on human monocytes. Using biotinylated protein, we provide evidence that protein SR binds to human monocytes in dose-, time-, and calcium-dependent manners through specific interactions. These results were confirmed by competition experiments using either soluble human monocyte extract or anti-SR immunoglobulin G. Binding occurred through lectin-like interactions between SR and carbohydrate portions of monocyte membrane glycoproteins, since binding could be inhibited by several sugars, especially fucose and N-acetylneuraminic acid (NANA), which were confirmed by ligand blotting to be the primer ligands recognized by SR on human monocyte extracts. The ability of protein SR to stimulate the production of cytokines by human circulating monocytes was then examined. The release of tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta, and interleukin 6 is time and dose dependent and not affected by the addition of polymyxin B. Activation of monocytes resulted from specific binding of SR to NANA and fucose present on cell surface glycoproteins since TNF-alpha release could be inhibited by sialidase and pronase treatment of monocytes and by NANA and fucose. These results confirm that sialic acid and fucose present on cell surface macromolecules and especially glycoproteins are needed for the binding of SR to monocytes and for the release of TNF-alpha.
Insights
Streptococcus mutans protein SR binds to human monocytes via specific sugar interactions, triggering the release of inflammatory cytokines like tumor necrosis factor alpha. This interaction is crucial for monocyte activation and subsequent inflammatory responses.
Area of Science:
- Immunology
- Microbiology
- Biochemistry
Background:
- Streptococcus mutans is a bacterium linked to dental caries.
- Protein SR from S. mutans is an antigen with potential roles in host-pathogen interactions.
- Human monocytes play a key role in initiating inflammatory and immune responses.
Purpose of the Study:
- To investigate the immunomodulatory effects of Streptococcus mutans protein SR on human monocytes.
- To elucidate the mechanism of protein SR binding to monocytes.
- To determine if protein SR can stimulate cytokine production in monocytes.
Main Methods:
- Biotinylated protein SR used to study binding kinetics (dose, time, calcium dependence).
- Competition assays with monocyte extracts and anti-SR antibodies.
- Ligand blotting to identify specific binding targets (sugars, glycoproteins).
- Measurement of cytokine release (TNF-alpha, IL-1beta, IL-6) from monocytes upon protein SR stimulation.
- Enzymatic treatment (sialidase, pronase) of monocytes to assess binding and activation mechanisms.
Main Results:
- Protein SR binds specifically to human monocytes in a dose-, time-, and calcium-dependent manner.
- Binding is mediated by lectin-like interactions with carbohydrate portions of monocyte glycoproteins, particularly fucose and N-acetylneuraminic acid (NANA).
- Protein SR stimulates the dose- and time-dependent release of TNF-alpha, IL-1beta, and IL-6 from monocytes.
- Monocyte activation and TNF-alpha release are dependent on sialic acid and fucose on cell surface glycoproteins.
Conclusions:
- Protein SR from Streptococcus mutans interacts specifically with human monocytes through recognition of cell surface glycoproteins containing fucose and NANA.
- This binding event triggers the production and release of pro-inflammatory cytokines, indicating a role for protein SR in modulating the host immune response.
- The findings highlight a mechanism by which oral bacteria may influence local and systemic inflammation.