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Of mice and men: Interaction of Corynebacterium diphtheriae strains with murine and human phagocytes
Dulanthi Weerasekera1, Tamara Fastner1, Roland Lang2
1a Department Biologie , Friedrich-Alexander-Universität Erlangen-Nürnberg , Erlangen , Germany.
Abstract:
Seven non-toxigenic C. diphtheriae strains and one toxigenic strain were analyzed with regard to their interaction with murine macrophages (BMM) and human THP-1 macrophage-like cells. Proliferation assays with BMM and THP-1 revealed similar intracellular CFUs for C. diphtheriae strains independent of the host cell. Strain ISS4060 showed highest intracellular CFUs, while the toxigenic DSM43989 was almost not detectable. This result was confirmed by TLR 9 reporter assays, showing a low signal for DSM43989, indicating that the bacteria are not endocytosed. In contrast, the non-pathogenic C. glutamicum showed almost no intracellular CFUs independent of the host cell, but was recognized by TLR9, indicating that the bacteria were degraded immediately after endocytosis. In terms of G-CSF and IL-6 production, no significant differences between BMM and THP-1 were observed. G-CSF production was considerably higher than IL-6 for all C. diphtheriae strains and the C. glutamicum did not induce high cytokine secretion in general. Furthermore, all corynebacteria investigated in this study were able to induce NFκB signaling but only viable C. diphtheriae strains were able to cause host cell damage, whereas C. glutamicum did not. The absence of Mincle resulted in reduced G-CSF production, while no influence on the uptake of the bacteria was observed. In contrast, when MyD88 was absent, both the uptake of the bacteria and cytokine production were blocked. Consequently, phagocytosis only occurs when the TLR/MyD88 pathway is functional, which was also supported by showing that all corynebacteria used in this study interact with human TLR2.
Insights
Corynebacterium diphtheriae interactions with macrophages depend on the Toll-like receptor/MyD88 pathway, influencing bacterial uptake and cytokine production. Non-toxigenic strains showed varied intracellular survival, while toxigenic strains were poorly detected.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Understanding the interaction between Corynebacterium diphtheriae and host immune cells is crucial for deciphering its pathogenesis.
- Macrophages play a key role in innate immunity against bacterial infections.
Purpose of the Study:
- To investigate the interaction of toxigenic and non-toxigenic Corynebacterium diphtheriae strains with murine macrophages (BMM) and human THP-1 cells.
- To elucidate the role of Toll-like receptors (TLRs) and downstream signaling pathways in this interaction.
Main Methods:
- Macrophage proliferation assays to determine intracellular bacterial survival (CFUs).
- TLR9 reporter assays to assess bacterial endocytosis.
- Cytokine (G-CSF, IL-6) production measurements.
- NFκB signaling pathway activation analysis.
- Experiments using knockout cell lines lacking Mincle or MyD88.
Main Results:
- Intracellular survival of C. diphtheriae strains varied, with strain ISS4060 showing the highest CFUs and the toxigenic strain DSM43989 being poorly detected.
- TLR9 reporter assays indicated poor endocytosis of the toxigenic strain DSM43989.
- All investigated corynebacteria induced NFκB signaling, but only viable C. diphtheriae caused host cell damage.
- G-CSF production was higher than IL-6 for C. diphtheriae, and Mincle absence reduced G-CSF but not bacterial uptake.
- MyD88 deficiency blocked both bacterial uptake and cytokine production, highlighting the TLR/MyD88 pathway's necessity for phagocytosis.
Conclusions:
- Phagocytosis of corynebacteria by macrophages is dependent on a functional TLR/MyD88 signaling pathway.
- C. diphtheriae interacts with human TLR2, and its uptake and subsequent immune response are mediated through TLR/MyD88.
- The study provides insights into the differential interaction of C. diphtheriae strains with macrophages, influencing immune responses.
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