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Mitogenic activity of bone marrow-derived mouse mast cells and mast cell lines P815 and MC/9 on B and T lymphocytes is present in their culture supernatants. To identify this activity, mast cells were incubated in serum-free medium and the supernatant was subjected to differential centrifugation, which resulted in two fractions, the hypodense and dense fraction (pellet). When analyzed for their mitogenic activity on spleen cells, all activity was found to be associated with the dense fraction. Electron microscopy studies revealed the presence in this fraction of small vesicles called exosomes with a heterogeneous size from 60 to 100 nm of diameter. When cocultured with spleen cells, purified exosomes induced blast formation, proliferation, as well as IL-2 and IFN-γ production, but no detectable IL-4. Similar data were obtained by injecting exosomes into naive mice. In contrast to mast cell lines, a pretreatment with IL-4 is required for bone marrow-derived mast cells to secrete active exosomes. Structurally, exosomes were found to harbor immunologically relevant molecules such as MHC class II, CD86, LFA-1, and ICAM-1. These findings indicate that mast cells can represent a critical component of the immunoregulatory network through secreted exosomes that display mitogenic activity on B and T lymphocytes both in vitro and in vivo.

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In this work a strategy for the control of structure and optical properties of inorganic luminescent oxide-based nanoparticles is presented. The nonaqueous sol-gel route is found to be suitable for the synthesis of hafnia nanoparticles and their doping with rare earths (RE) ions, which gives rise to their luminescence either under UV and X-ray irradiation. Moreover, we have revealed the capability of the technique to achieve the low-temperature stabilization of the cubic phase through the effective incorporation of trivalent RE ions into the crystal lattice. Particular attention has been paid to doping with europium, causing a red luminescence, and with lutetium. Structure and morphology characterization by XRD, TEM/SEM, elemental analysis, and Raman/IR vibrational spectroscopies have confirmed the occurrence of the HfO2 cubic polymorph for dopant concentrations exceeding a threshold value of nominal 5 mol %, for either Lu(3+) or Eu(3+). The optical properties of the nanopowders were investigated by room temperature radio- and photoluminescence experiments. Specific features of Eu(3+) luminescence sensitive to the local crystal field were employed for probing the lattice modifications at the atomic scale. Moreover, we detected an intrinsic blue emission, allowing for a luminescence color switch depending on excitation wavelength in the UV region. We also demonstrate the possibility of changing the emission spectrum by multiple RE doping in minor concentration, while deputing the cubic phase stabilization to a larger concentration of optically inactive Lu(3+) ions. The peculiar properties arising from the solvothermal nonaqueous synthesis here used are described through the comparison with thermally treated powders.