NR4A1-dependent Ly6Clow monocytes contribute to reducing joint inflammation in arthritic mice through Treg cells.

Monocytes are central to the physiopathology of arthritis, but their roles in progression and resolution of the disease remain to be clarified. Using NR4A1-/- mice, which lack patrolling lymphocyte antigen 6C (Ly6Clow ) monocytes, we found that inflammatory Ly6Chigh monocytes contribute to rapid development of arthritis in a serum transfer-induced arthritis (STIA) model. Our experiments suggest that patrolling monocytes do not promote the initiation and progression of arthritis in mice, as severity of symptoms was amplified in NR4A1-/- mice. Moreover, we show that treatment of arthritic wild type (WT) mice with cytosporone B (Csn-B), a NR4A1-specific agonist, significantly reduces severity of disease. Effects of Csn-B were absent in monocyte-depleted mice treated with clodronate until Ly6Clow monocytes were restored. Adoptive transfer of Ly6Clow monocytes in arthritic NR4A1-/- mice treated with Csn-B reduces joint inflammation, supporting the regulatory role of Ly6Clow subset on disease development. Our results also reveal that administration of Csn-B to arthritic mice enhances levels of circulating CD4+ CD25+ FoxP3+ Treg cells, a process requiring the presence of Ly6Clow monocytes. Together, these data indicate that Ly6Chigh monocytes are involved in the initiation and progression of arthritis and Ly6Clow monocytes contribute to reduce joint inflammation through the mobilization of Treg cells.

TAK1 contributes to the enhanced responsiveness of LTB(4)-treated neutrophils to Toll-like receptor ligands.

Pattern-recognition receptors such as Toll-like receptors (TLRs) are essential sensors implicated in the early and efficient innate immune response against pathogens. We have previously demonstrated that leukotriene B(4)(LTB(4)) has the capacity to enhance leukocyte responses to TLR9 ligands and to control viral infection. In this report, we provide evidence that LTB(4) treatment of human neutrophils leads to a potentiation in proinflammatory cytokine secretion induced by various myeloid differentiation factor 88-dependent TLR agonists. LTB(4) failed to enhance TLR mRNA levels as well as expression of TLR2 and TLR4 receptors, suggesting that LTB(4) acts through intracellular mechanism(s) to potentiate neutrophil responses to TLR ligands. We found that while IRAK can be activated by LTB(4), this process is dispensable to LTB(4) to potentiate neutrophil responses to TLR ligands since pretreatment of neutrophils with IRAK1/4 inhibitor did not affect its potentiating effects. However, our data clearly show that LTB(4) treatment of neutrophils led to the phosphorylation of downstream signaling molecules, TAK1 and p38, a process found essential to observe an increased secretion of cytokines by neutrophils activated with TLR ligands. Pretreatment of neutrophils with TAK1 or p38 kinase inhibitors strongly repressed the effect of LTB(4) on cytokine synthesis by neutrophils stimulated with LTA, LPS or CpG. The same pattern was observed in agonist-treated human embryonic kidney 293 cells transfected with TAK1-targeting siRNA where secretion of IL-8 was significantly reduced to basal levels. These results indicate that TAK1 and p38 kinases appear to be central in the 'priming effect' of LTB(4) on neutrophils to enhance response to TLR ligands.

Role of the extracellular matrix proteins in the resistance of SP6.5 uveal melanoma cells toward cisplatin.

Uveal melanoma is the most frequent primary intraocular tumor in the adult population. This malignancy has a high mortality rate and responds poorly to existing chemotherapy. Recently, the tumor environment has been found to exert a profound influence on drug response through cell interaction with components from the extracellular matrix (ECM). In the present study, we investigated whether individual components from the ECM may affect cell survival and/or cell death induced by the cytotoxic agent cisplatin on the SP6.5 uveal melanoma cell line. Tumor cells were shown by immunofluorescence analyses to be surrounded by the ECM proteins fibronectin (FN), type IV collagen (CIV) and laminin (LM), both at the primary and metastatic sites. Binding of SP6.5 cells to FN, LM and CIV is primarily dictated by the expression of membrane bound integrins from the beta1 family as revealed by cell adhesion assays conducted on ECM-coated culture plates. Analysis of cell death by flow cytometry demonstrated that culturing SP6.5 cells in the presence of FN, CIV and LM, substantially reduced the percentage of cells undergoing apoptosis after cisplatin treatment when compared with those seeded on a non-permissive matrix. These results suggest that adhesion of the SP6.5 uveal melanoma cells to the ECM proteins FN, CIV and LM might therefore confer resistance to the chemotherapeutic agent cisplatin. The cellular resistance induced by the ECM proteins toward cisplatin could explain in part the local recurrence of metastasis derived from uveal melanoma often observed clinically after chemotherapy.

Epstein-Barr virus interferes with the amplification of IFNalpha secretion by activating suppressor of cytokine signaling 3 in primary human monocytes.

BACKGROUND: Epstein-Barr virus is recognized to cause lymphoproliferative disorders and is also associated with cancer. Evidence suggests that monocytes are likely to be involved in EBV pathogenesis, especially due to a number of cellular functions altered in EBV-infected monocytes, a process that may affect efficient host defense. Because type I interferons (IFNs) are crucial mediators of host defense against viruses, we investigated the effect of EBV infection on the IFNalpha pathway in primary human monocytes. METHODOLOGY/PRINCIPAL FINDINGS: Infection of monocytes with EBV induced IFNalpha secretion but inhibited the positive feedback loop for the amplification of IFNalpha. We showed that EBV infection induced the expression of suppressor of cytokine signaling 3 (SOCS3) and, to a lesser extent, SOCS1, two proteins known to interfere with the amplification of IFNalpha secretion mediated by the JAK/STAT signal transduction pathway. EBV infection correlated with a blockage in the activation of JAK/STAT pathway members and affected the level of phosphorylated IFN regulatory factor 7 (IRF7). Depletion of SOCS3, but not SOCS1, by small interfering RNA (siRNA) abrogated the inhibitory effect of EBV on JAK/STAT pathway activation and significantly restored IFNalpha secretion. Finally, transfection of monocytes with the viral protein Zta caused the upregulation of SOCS3, an event that could not be recapitulated with mutated Zta. CONCLUSIONS/SIGNIFICANCE: We propose that EBV protein Zta activates SOCS3 protein as an immune escape mechanism that both suppresses optimal IFNalpha secretion by human monocytes and favors a state of type I IFN irresponsiveness in these cells. This immunomodulatory effect is important to better understand the aspects of the immune response to EBV.