Accumulation of MFG-E8/lactadherin on exosomes from immature dendritic cells

Blood Cells Mol Dis. Sep-Oct 2005;35(2):81-8. doi: 10.1016/j.bcmd.2005.05.001.

Abstract

Exosomes are vesicles of endocytic origin secreted spontaneously by dendritic cells (DCs). We have shown previously that exosomes can transfer antigen or MHC-peptide complexes between DCs, thus potentially amplifying the immune response. We had also identified milk fat globule EGF/factor VIII (MFG-E8), also called lactadherin, as one of the major exosomal proteins. MFG-E8 has two domains: an Arg-Gly-Asp sequence that binds integrins alphavbeta3 and alphavbeta5 (expressed by human DCs and macrophages) and a phosphatidyl-serine (PS) binding sequence through which it associates to PS-containing membranes (among which exosomes). MFG-E8 is thus a good candidate molecule to address exosomes to DCs. Here, we show that MFG-E8 is expressed by immature bone-marrow-derived DCs (BMDCs) and secreted in association with exosomes in vitro. We have generated mice expressing an inactive form of MFG-E8, fused to beta-galactosidase. Analyzing these mice, we demonstrate that MFG-E8 is expressed in vivo in splenic DCs. In a mouse DC-dependent, antigen-specific, CD4 T cell-stimulation assay, exosomes produced by MFG-E8-deficient BMDCs were barely less efficient than exosomes bearing MFG-E8. We conclude that MFG-E8 is efficiently targeted to exosomes but is not essential to address exosomes to mouse BMDCs. Involvement of MFG-E8/lactadherin in exosome targeting to other DC subpopulations, or to human DCs, is still possible.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigen Presentation
  • Antigens, Surface / immunology
  • Antigens, Surface / metabolism*
  • Bone Marrow Cells
  • CD4-Positive T-Lymphocytes / immunology
  • Cell Communication / immunology
  • Dendritic Cells / chemistry*
  • Dendritic Cells / immunology*
  • Dendritic Cells / metabolism
  • Endosomes / chemistry*
  • Endosomes / metabolism
  • Lymphocyte Activation / immunology
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Milk Proteins / immunology
  • Milk Proteins / metabolism*
  • Spleen / cytology

Substances

  • Antigens, Surface
  • Mfge8 protein, mouse
  • Milk Proteins