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Extracellular vesicles from methicillin resistant Staphylococcus aureus stimulate proinflammatory cytokine production
Krisana Asano1,2, Shouhei Hirose1, Kouji Narita1,3
1Department of Microbiology and Immunology, Hirosaki University Graduate School of Medicine, Hirosaki, Aomori, Japan.
Abstract:
Extracellular vesicles (EVs) released from bacteria are enclosed particles carrying biological active molecules. They have been shown to play a role in bacterial communications and delivery of virulence factors to the host cells. Staphylococcus aureus is an opportunistic pathogen causing a variety of infections ranging from impetigo to septicaemia. The EVs released from S. aureus have a high potential to be used for vaccine development against S. aureus infections. However, it is important to clearly understand the impact of SaEVs on the host's immune response. Our study demonstrated that purified EVs from a clinical isolated methicillin-resistant S. aureus (SaEVs) significantly stimulated proinflammatory cytokine production in mouse immune cells and induced host cell death. An impairment of cytokine production in the Toll-like receptor (TLR)-silenced macrophages suggested that SaEVs stimulate proinflammatory response via TLRs 2, 4 and 9. In mouse infection model, the results demonstrated that SaEV immunization did not provide protective effect. In contrast, all SaEV-immunized mice died within Day 1 after methicillin-resistant S. aureus (MRSA) infection. After MRSA infection for 3 h, the production of IL-6, TNF-α and IL-17 in the spleen of SaEV-immunized mice was significantly higher than that of control mice. On Day 5 after the second immunization, total IgE in the serum was significantly enhanced, and a high titre of Th2-related cytokines was remarkably induced after ex vivo stimulation of the spleen cells with SaEVs. These results suggested that MRSA-derived EVs act as an immunostimulant that induces inflammatory response and IgE-mediated hypersensitivity after MRSA infection.
Insights
Extracellular vesicles from Staphylococcus aureus (SaEVs) stimulate inflammation and host cell death via Toll-like receptors. SaEV immunization worsened MRSA infection outcomes, indicating immunostimulatory rather than protective effects.
Area of Science:
- Microbiology
- Immunology
- Vaccine Development
Background:
- Extracellular vesicles (EVs) from bacteria mediate communication and virulence.
- Staphylococcus aureus (S. aureus) infections pose significant health risks.
- S. aureus EVs (SaEVs) show potential for vaccine development, but their immunomodulatory effects require clarification.
Purpose of the Study:
- To investigate the impact of methicillin-resistant S. aureus (MRSA)-derived EVs (SaEVs) on host immune responses.
- To determine the role of Toll-like receptors (TLRs) in SaEV-mediated immune stimulation.
- To evaluate the efficacy of SaEV immunization in a mouse model of MRSA infection.
Main Methods:
- Purification of SaEVs from a clinical MRSA isolate.
- Assessment of SaEVs' effect on cytokine production and cell death in mouse immune cells.
- Analysis of TLR involvement using TLR-silenced macrophages.
- Evaluation of SaEV immunization in a mouse MRSA infection model, including immune cell and cytokine profiling.
Main Results:
- SaEVs significantly stimulated proinflammatory cytokine production (IL-6, TNF-α, IL-17) and induced host cell death.
- SaEVs activate immune responses via TLRs 2, 4, and 9.
- SaEV immunization did not protect against MRSA infection; instead, it led to increased mortality and exacerbated inflammatory responses.
- SaEV immunization enhanced total IgE and induced Th2-related cytokines, suggesting hypersensitivity.
Conclusions:
- MRSA-derived EVs act as potent immunostimulants, triggering inflammatory responses and potentially IgE-mediated hypersensitivity.
- SaEVs' immunostimulatory properties, rather than protective immunity, were demonstrated in this study.
- Further research is needed to understand the complex role of SaEVs in host-pathogen interactions and to guide vaccine strategies.
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