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The influence of curli, a MHC-I-binding bacterial surface structure, on macrophage-T cell interactions
C Johansson1, T Nilsson, A Olsén
1Department of Cell and Molecular Biology, Section of Immunology, Lund University, Sweden.
Abstract:
Escherichia coli express thin surface fimbriae called curli which bind soluble matrix proteins and major histocompatibility complex (MHC)-I molecules. The present study addressed the ability of purified curli or curliated E. coli to influence peptide presentation on MHC-I, T cell proliferation and bacterial uptake by macrophages. In vitro studies with curli-proficient E. coli YMel and the isogenic curli-deficient strain YMel-1, both expressing the model antigen Crl-OVA, showed that curli expression by E. coli does not appear to influence the efficiency by which the bacteria are processed by murine macrophages for OVA(257-264) presentation on K(b). Furthermore, curli expression by E. coli did not influence the binding of exogenously added OVA(257-264) peptide to K(b) on the surface of prefixed macrophages. In addition, neither curliated nor non-curliated heat-killed bacteria influenced proliferation of either murine or human T cells stimulated with anti-CD3. Finally, curliated E. coli adhered to and were internalized by macrophages from C57BL/6 and MHC-I-deficient TAP1(-/-) mice equally well. Together these studies show that curli expression by E. coli does not appear to influence phagocytic processing of bacteria expressing Crl-OVA for OVA(257-264)/K(b) presentation, the binding of exogenously added OVA(257-264) to K(b) or T cell proliferation. In addition, although curli expression by E. coli enhances bacterial interaction with macrophages, curli interaction with MHC-I does not significantly contribute to this adherence.
Insights
Escherichia coli curli fimbriae do not affect antigen presentation on MHC-I molecules or T cell proliferation. While curli enhance bacterial interaction with macrophages, they do not significantly contribute to adherence or antigen processing for presentation.
Area of Science:
- Immunology
- Microbiology
- Cell Biology
Background:
- Escherichia coli produce curli fimbriae, surface protein structures that bind matrix proteins and MHC-I molecules.
- Curli's potential role in modulating host immune responses, specifically antigen presentation and T cell activation, remains incompletely understood.
Purpose of the Study:
- To investigate the impact of curli expression by E. coli on peptide presentation via MHC-I molecules.
- To assess the influence of curli on T cell proliferation and macrophage uptake of bacteria.
- To determine the contribution of curli-MHC-I interactions to bacterial adherence and internalization by macrophages.
Main Methods:
- In vitro studies using curli-proficient and deficient E. coli strains expressing a model antigen (Crl-OVA).
- Analysis of OVA(257-264) peptide presentation on MHC-I (K(b)) in murine macrophages.
- Assessment of T cell proliferation using anti-CD3 stimulation with heat-killed bacteria.
- Macrophage uptake assays using C57BL/6 and MHC-I-deficient (TAP1(-/-)) mice.
Main Results:
- Curli expression did not alter the processing of E. coli for OVA(257-264) presentation on K(b) by murine macrophages.
- Exogenous OVA(257-264) peptide binding to K(b) on macrophages was not influenced by curli.
- Neither curliated nor non-curliated bacteria affected T cell proliferation.
- Curliated E. coli adhered to and were internalized by macrophages similarly to non-curliated bacteria, irrespective of MHC-I deficiency.
Conclusions:
- Curli expression by E. coli does not significantly influence antigen processing for MHC-I presentation, T cell proliferation, or bacterial uptake by macrophages.
- While curli enhance bacterial interaction with macrophages, curli-MHC-I binding does not play a major role in this adherence.