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Bone marrow-derived dendritic cells can process bacteria for MHC-I and MHC-II presentation to T cells
M Svensson1, B Stockinger, M J Wick
1Department of Cell and Molecular Biology, Lund University, Sweden.
Abstract:
Dendritic cells can engulf particulate Ags and induce T cell proliferative responses after pulsing with particulate Ag. However, their capacity to process viable Gram-negative bacteria for presentation by MHC-I and MHC-II has not been shown. We therefore characterized the ability of murine bone marrow-derived dendritic cells to process Escherichia coli and Salmonella typhimurium, expressing defined epitopes for presentation by MHC-I and MHC-II molecules. The I-Ak-restricted 46-61 epitope from hen egg white lysozyme (HEL(46-61)) or the Kb-restricted 257-264 epitope from chicken egg OVA (OVA(257-264)) was expressed as fusion proteins in the bacterial cytoplasm as the Crl-HEL and Crl-OVA fusion proteins, respectively. Bacteria expressing Crl-HEL or Crl-OVA, or beads coated with HEL or OVA, were coincubated with murine bone marrow-derived dendritic cells, and Ag processing and presentation were quantitated using T cell hybridomas. The data show that granulocyte-macrophage CSF-stimulated dendritic cells can process live intact Gram-negative bacteria for peptide presentation by MHC-I and MHC-II. Cytochalasin D inhibition studies revealed that processing for both MHC-I and MHC-II presentation required cytoskeletal rearrangements. Processing for MHC-I and MHC-II presentation was inhibited by ammonium chloride, suggesting that acidic compartments were required. Thus, granulocyte-macrophage CSF-stimulated murine bone marrow dendritic cells are capable of processing exogenous particulate Ags, including bacteria with no known mechanism for phagosomal escape, for peptide presentation by both MHC-I and MHC-II. These data suggest that dendritic cells may be important in priming both CD4+ and CD8+ T cells to bacterial Ags.
Insights
Dendritic cells can process live Gram-negative bacteria for presentation to T cells. This processing requires cytoskeletal rearrangement and acidic compartments, suggesting a role in priming both CD4+ and CD8+ T cells against bacterial antigens.
Area of Science:
- Immunology
- Cell Biology
- Microbiology
Background:
- Dendritic cells (DCs) are crucial antigen-presenting cells.
- DCs engulf particulate antigens and stimulate T cell responses.
- The capacity of DCs to process viable Gram-negative bacteria for MHC-I and MHC-II presentation remains unclear.
Purpose of the Study:
- To investigate the ability of murine bone marrow-derived dendritic cells to process Escherichia coli and Salmonella typhimurium.
- To determine if these bacteria can be processed for presentation by MHC-I and MHC-II molecules.
Main Methods:
- Murine bone marrow-derived dendritic cells were stimulated with granulocyte-macrophage colony-stimulating factor (GM-CSF).
- DCs were coincubated with live Gram-negative bacteria (E. coli, S. typhimurium) expressing model antigens or antigen-coated beads.
- Antigen processing and presentation by MHC-I and MHC-II were quantified using T cell hybridomas.
- Inhibition studies used cytochalasin D and ammonium chloride to investigate cellular mechanisms.
Main Results:
- GM-CSF-stimulated DCs successfully processed live, intact Gram-negative bacteria for presentation via MHC-I and MHC-II.
- Processing for both MHC-I and MHC-II presentation necessitated cytoskeletal rearrangements.
- Inhibition of acidic compartments with ammonium chloride impaired antigen presentation.
- DCs efficiently processed exogenous particulate antigens, including bacteria lacking phagosomal escape mechanisms.
Conclusions:
- Murine bone marrow-derived dendritic cells can process viable Gram-negative bacteria for presentation on both MHC-I and MHC-II.
- Bacterial antigen processing by DCs involves cytoskeletal dynamics and acidic endosomal compartments.
- These findings highlight the significant role of dendritic cells in initiating adaptive immune responses against bacterial pathogens by priming both CD4+ and CD8+ T cells.