SUMMARY MicroRNAs regulate the function of several immune cells but their role in promoting CD8+ T-cell immunity remains unknown. Here we report that miR-155 is required for CD8+ T-cell responses to both virus and cancer. In the absence of miR-155, accumulation of effector CD8+ T cells was severely reduced during acute and chronic viral infections and control of virus replication was impaired. Similarly, Mir155-/- CD8+ T cells were in effective at controlling tumor growth, whereas miR-155 overexpression enhanced the antitumor response. miR-155 deficiency resulted in accumulation of SOCS-1 causing defective cytokine signaling through STAT5. Consistently, enforced expression of SOCS-1 in CD8+ T cells phenocopied the miR-155 deficiency, whereas SOCS-1 silencing augmented tumor destruction. These findings identify miR-155 and its target SOCS-1 as key regulators of effector CD8+ T cells that can be modulated to potentiate immunotherapies for infectious diseases and cancer.

Human TLR10 is an orphan member of the TLR family. Genomic studies indicate that TLR10 is in a locus that also contains TLR1 and TLR6, two receptors known to function as coreceptors for TLR2. We have shown that TLR10 was not only able to homodimerize but also heterodimerized with TLRs 1 and 2. In addition, unlike TLR1 and TLR6, TLR10 was expressed in a highly restricted fashion as a highly N-glycosylated protein, which we detected in B cell lines, B cells from peripheral blood, and plasmacytoid dendritic cells from tonsil. We were also able to detect TLR10 in a CD1a+ DC subset derived from CD34+ progenitor cells which resemble Langerhans cells in the epidermis. Although we were unable to identify a specific ligand for TLR10, by using a recombinant CD4TLR10 molecule we also demonstrated that TLR10 directly associates with MyD88, the common Toll IL-1 receptor domain adapter. Additionally, we have characterized regions in the Toll IL-1 receptor domain of TLR10 that are essential in the activation of promoters from certain inflammatory cytokines. Even though TLR10 expression has not been detected in mice, we have identified a partial genomic sequence of the TLR10 gene that was present but nonfunctional and disrupted by a retroviral insertion in all mouse strains tested. However, a complete TLR10 sequence could be detected in the rat genome, indicating that a functional copy may be preserved in this species.

Studies involving Toll-like receptor 3 (TLR3)-deficient mice suggest that this receptor binds double-stranded RNA. In the present study, we analyzed ligand/receptor interactions and receptor-proximal events leading to TLR3 activation. The mutagenesis approach showed that certain cysteine residues and glycosylation in TLR3 amino-terminal leucine-rich repeats were necessary for ligand-induced signaling. Furthermore, inactive mutants had a dominant negative effect, suggesting that the signaling module is a multimer. We constructed a chimeric molecule fusing the amino-terminal ectodomain of TLR3 to the transmembrane and carboxyl terminal domains of CD32a containing an immunoreceptor tyrosine-based motif. Expression of TLR3-CD32 in HEK293T cells and the myeloid cell line U937 resulted in surface localization of the receptor, whereas the nonrecombinant molecule was intracellularly local- Mammalian Toll-like receptors (TLRs) 7 belong to a family of receptors that recognize pathogen-associated molecular patterns. TLRs play a key role in host defense during pathogen infection by regulating and linking the innate and adaptive immune responses (1-3). TLRs are expressed in dendritic cells (DC), sentinels of the immune system, endowing them with the capacity to sense pathogen-derived products and to alert the immune system (4). Members of the TLR family are also variably expressed on nonhematopoietic cells. TLR-deficient mice and transfected cell lines have been the keys to understanding TLR function. Ligand specificity has been elucidated for most TLRs; thus, TLR2 and TLR4 recognize Gram-positive and Gram-negative bacterial cell wall products, respectively. TLR5 recognizes a structural epitope of bacterial flagellin, and TLR7, TLR8, and TLR9 have been demonstrated to recognize different forms of microbial-derived nucleic acid (5). Host-derived ligands for the TLRs have also been identified; in particular, TLR4 recognizes heat shock proteins and pulmonary surfactant (6), and TLR9 recognizes chromatin-IgG complexes (7).TLR3 has been extensively characterized to be a receptor for poly(I-C), a synthetic double-stranded RNA (dsRNA) mimic (8); recently, it has been shown to mediate responses to West Nile virus (9) as well as dsRNA derived from the helminth parasite Schistosoma (10). Additionally, host-derived mRNA has recently been shown to activate TLR3, suggesting that activation via TLR3 can occur in a variety of situations (11). Whereas most TLRs recruit myeloid differentiation factor 88 (12), with some variation in the signaling profile mediated by the additional recruitment of Toll/interleukin-1 receptor-containing adapter protein and TRIF-related adaptor molecule, TLR3 recruits only TRIF (13-15). TRIF can activate both NF-B through TRAF6 and receptor-interacting protein-1 (16) and interferon-regulatory factor 3 through IB kinase/ TANK-binding kinase 1 (17) and phosphoinositide 3-kinase (18). Although the signaling pathway of TLRs is increasingly well characterized, the parameters controlling interactions between the recept...

We have isolated a novel cell surface molecule, the human homolog of osteoclast-associated receptor (OSCAR). Unlike mouse OSCAR, hOSCAR is widely transcribed in cells of the myeloid lineage. Notably, hOSCAR is expressed on circulating blood monocytes and CD11c ؉ dendritic cells but not on T and B cells. hOSCAR is continually expressed during differentiation of CD14 ؉ monocytes into dendritic cells and maintained after maturation. hOSCAR associates with the FcR␥ as shown by translocation of FcR␥ to the cell surface in presence of hOSCAR and coimmunoprecipitation from transfected cell lines and ex vivo cells. Engagement of hOSCAR with specific mAb leads to Ca 2؉ mobilization and cytokine release, indicators of cellular activation. Endocytosis of the receptor in dendritic cells was observed, followed by passage of the internalized material into Lamp-1 ؉ and HLA-DR ؉ compartments, suggesting a role in antigen uptake and presentation.Dendritic cells were able to stimulate a T-cell clone specific for an epitope of mouse IgG1 after uptake and processing of the hOSCAR-specific antibody, demonstrating the capacity of this receptor to mediate antigen presentation. hOSCAR thus represents a novel class of molecule expressed by dendritic cells involved in the initiation of the immune response.