Exosomes may contribute to cell-cell communication at the level of immunological synapses or at a distance, by delivering mRNA and miRNA modifying the recipient cell protein production and gene expression. The present study aims to determine whether the effect of ILT3Fc on allostimulated CD8 T cells is accompanied by changes in the miRNA content of exosomes generated during allostimulation.Exosomes were isolated from culture supernatants of MLC in which CD3 T cells had been stimulated with allogeneic APC in the presence or absence of ILT3Fc. The identity and relative quantity of the exosomal miRNA content was determined by RT-PCR. The inhibitory or inflammatory properties of these exosomes were evaluated by 24h pretreatment of sorted CD8 Ts from MLC containing ILT3Fc. The CD8 T cells were then tested for the effect on the proliferation of naive, syngeneic T cells primed in response to the same stimulating APC.CD8 Ts primed in the presence of ILT3Fc inhibit syngeneic CD4 T cell responses by >80%. When CD8 Ts are pretreated with inflammatory exosomes, and are used in MLC at lower than 1:1 ratios to respoding Th cells, they lose inhibitory activity. These exosomes contain miRNA-21, -30b, -146a, -155, -395, and Let7a, known to be increased in T cells during activation. In contrast, exosomes obtained from T cells primed in the presence of ILT3Fc, do not abolish CD8 Ts inhibitory potential, suggesting that ILT3Fc blocks the release into the medium or alters the RNA content of inflammatory exosomes.Micro RNA contained by exosomes released from alloactivated T cells enhance T helper activity even in the presence of T suppressor cells. This suggests the potential use of exosomal inflammatory miRNA as a monitor of cellular immune responses against the graft. Furthermore, such exosomes may be of use in eliciting immune T cell responses against tumors or microbial agents.