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Related Experiment Videos

Modulation of antigen processing and presentation by covalently linked complement C3b fragment

M R Jacquier-Sarlin1, F M Gabert, M B Villiers

  • 1Unité INSERM 238, Centre d'Etudes Nucléaires de Grenoble, France.

Immunology
|January 1, 1995
PubMed
Summary

Complement fragment C3b binding to antigen tetanus toxin (TT) enhances T-cell proliferation but delays antigen processing. This occurs because C3b inhibits cathepsin D, a key protease in antigen breakdown, impacting antigen presentation by antigen-presenting cells (APCs).

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Area of Science:

  • Immunology
  • Biochemistry
  • Cell Biology

Background:

  • Antigen presentation by antigen-presenting cells (APCs) is crucial for T-cell activation.
  • Ligands binding to antigens (Ag) before uptake can modulate antigen processing and presentation.
  • Complement protein C3b, a fragment of C3, can covalently bind to antigens via a reactive thiolester bond.

Purpose of the Study:

  • To investigate how covalent binding of C3b to tetanus toxin (TT) affects its processing and presentation by APCs.
  • To analyze the impact of C3b-bound TT on T-cell proliferation and antigen processing kinetics.

Main Methods:

  • Preparation of ester-linked complexes of TT and C3b.
  • Analysis of TT proteolysis using endosome/lysosome-enriched subcellular fractions and protease inhibitors.

Related Experiment Videos

  • Assessment of T-cell proliferation stimulation by APCs presenting TT or C3b-TT.
  • Enzymatic assays using purified cathepsins B and D to determine TT proteolysis by C3b.

    • Main Results:

    • Covalent binding of C3b to TT significantly increased and prolonged specific T-cell proliferation.
    • Proteolysis of TT was delayed when associated with C3b, as shown by SDS-PAGE analysis.
    • C3b binding to TT completely abolished its proteolysis by cathepsin D but preserved it with cathepsin B.

    Conclusions:

    • C3b binding to antigens enhances their presentation and T-cell stimulation.
    • The delay in antigen processing is attributed to C3b's inhibitory effect on cathepsin D.
    • These findings highlight a mechanism by which complement opsonization influences adaptive immune responses.