It is known that phospholipid phosphatidylserine (PS) exposure on cellular membranes, vesicles and liposomes stimulates anti-inflammatory responses and induces the release of immunoregulatory factors like TGF-b1, an important mediator of the process of malignant progression. Preliminary results of our group have demonstrated that B16F10 cells, a high-metastatic malignant melanoma cell line, produce large quantities of vesicles in vitro, and both cells and vesicles were able to up-regulate TGF-b1 production by professional phagocytes. These data, together with the fact that tumor cell vesiculation has been related to the acquisition of metastatic capability and to evasion from immune surveillance, led us to postulate the involvement of PS exposure and vesicles production in the establishment of malignant melanoma. In the present study, we show that tumoral microparticles carry tumor surface molecules, which includes the phospholipid PS itself (data observed by FACs analysis, fluorescence microscopy and transmission electron microscopy), as well as the ganglioside GM3, involved on melanoma B16F10 progression. In in vivo assays, we have observed that sensitization with vesicles prior to B16F10 intravenous innoculum increases the number of pulmonary tumor nodules in C57BL/6 mice (syngeneic hosts). This increase was not observed in the animals pre-sensitized with annexin treated vesicles or with those purified from cell cultures with low gangliosides exposure, which suggests the involvement of both ganglioside and PS molecules on the modulation of the anti-tumoral autologous response by these microparticles. Furthermore, vesicles addition over melanoma cells innoculum allowed tumor development in BALB/c mice, a strain that would normally sustain an efficient antitumoral alogenic response. Altogether, our data suggest a potential role for melanoma vesicles in tumor establishment, possibly by the negative regulation of anti-tumoral immune responses.

Supported by: INCa/FAF, CNPq.