Nonspecific B and T cell-stimulatory activity mediated by mast cells is associated with exosomes

Bone marrow-derived mouse mast cells (BMMC) and mast cell lines P815 and MC 9 have recently been shown to induce antigen-independent B and T lymphocyte activation. It has been demonstrated that a physical contact between mast cells and B and T lymphocytes is not necessary since mast cell supernatants contain full activity. Electron microscopy studies revealed the presence i n mast cell supernatants of small vesicles called exosomes with a heterogen eous size from 60 to 100 nm of diameter, When cocultured with spleen cells, purified exosomes induce B and T cell blast formation, proliferation as we ll as IL-2 and IFN-gamma production. In contrast to P815 and MC9 mast cell lines, a pretreatment with IL-4 is required for BMMC to produce active exos omes. Structurally, these exosomes were found to harbor immunologically rel evant molecules such as MHC class II, CD86, LFA-1 and ICAM-1. Here we provi de for the first time the evidence that mast cells use exosomes as sophisti cated messengers to communicate with cells of the immune system, Copyright (C) 2001 S. Karger AG, Basel.