The influence of curli, a MHC-I-binding bacterial surface structure, on macrophage–T cell interactions

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.

Force spectra of single bacterial amyloid CsgA nanofibers

“…4,5 CsgA nanobers, which are the major protein constituents of Escherichia coli (E. coli) extracellular biolms, provide adhesion, stiffness and mechanical stability for the biolms and play critical roles in the binding of host cells for internalization and protection against phage attack. [6][7][8] CsgA protein monomers, which consist of ve repeating units with several conservative residues, can fold into a compact b-helix which is capable of self-assembling into CsgA nanobers (Fig. 1a).…”

In Vitro Polymerization of a Functional Escherichia coli Amyloid Protein

“…The first example of a functional amyloid in bacteria was curli (12). Curli compose part of the complex extracellular matrix that is required for biofilm formation (17)(18)(19), host cell adhesion (20), and invasion (21,22), and they are proposed to be important stimulants of the host inflammatory response (23)(24)(25). An intriguing question is whether these functional amyloid proteins polymerize in a manner similar to disease-associated amyloids.…”