Daniela Bosisio

Chemerin expression marks early psoriatic skin lesions and correlates with plasmacytoid dendritic cell recruitment

Psoriasis is a type I interferon-driven T cell–mediated disease characterized by the recruitment of plasmacytoid dendritic cells (pDC) into the skin. The molecules involved in pDC accumulation in psoriasis lesions are unknown. Chemerin is the only inflammatory chemotactic factor that is directly active on human blood pDC in vitro. The aim of this study was to evaluate the role of the chemerin/ChemR23 axis in the recruitment of pDC in psoriasis skin. Prepsoriatic skin adjacent to active lesions and early lesions were characterized by a strong expression of chemerin in the dermis and by the presence of CD15+ neutrophils and CD123+/BDCA-2+/ChemR23+ pDC. Conversely, skin from chronic plaques showed low chemerin expression, segregation of neutrophils to epidermal microabscesses, and few pDC in the dermis. Chemerin expression was localized mainly in fibroblasts, mast cells, and endothelial cells. Fibroblasts cultured from skin of psoriatic lesions expressed higher levels of chemerin messenger RNA and protein than fibroblasts from uninvolved psoriatic skin or healthy donors and promoted pDC migration in vitro in a chemerin-dependent manner. Therefore, chemerin expression specifically marks the early phases of evolving skin psoriatic lesions and is temporally strictly associated with pDC. These results support a role for the chemerin/ChemR23 axis in the early phases of psoriasis development.

Toll-like receptors: a growing family of immune receptors that are differentially expressed and regulated by different leukocytes.

Toll is a Drosophila gene essential for ontogenesis and antimicrobial resistance. Several hortologues of Toll have been identified and cloned in vertebrates, namely Toll‐like receptors (TLR). Human TLR are a growing family of molecules involved in innate immunity. TLR are structurally characterized by a cytoplasmic Toll/interleukin‐1R (TIR) domain and by extracellular leucine‐rich repeats. TLR characterized so far activate the My D88/IRAK signaling cascade, which bifurcates and leads to NF‐κB and c‐Jun/ATF2/TCF activation. Genetic, gene transfer, and dominant‐negative approaches have involved TLR family members (TLR2 and TLR4) in lipopolysaccharide recognition and signaling. Accumulating evidence suggests that some TLR molecules are also involved in signaling receptor complexes that recognize components of gram‐positive bacteria and mycobacteria. However, the definitive role of other TLR is still lacking. A systematic approach has been used to determine whether different human leukocyte populations selectively or specifically expressed TLR mRNA. Based on expression pattern, TLR can be classified as ubiquitous (TLR1), restricted (TLR2, TLR4, and TLR5), and specific (TLR3). Expression and regulation of distinct though overlapping ligand recognition patterns may underlie the existence of a numerous, seemingly redundant, TLR family. Alternately, the expression of a TLR in a single cell type may indicate a specific role for this molecule in a restricted setting. J. Leukoc. Biol. 67: 450–456; 2000.

A hyper-dynamic equilibrium between promoter-bound and nucleoplasmic dimers controls NF-κB-dependent gene activity

Because of its very high affinity for DNA, NF‐κB is believed to make long‐lasting contacts with cognate sites and to be essential for the nucleation of very stable enhanceosomes. However, the kinetic properties of NF‐κB interaction with cognate sites in vivo are unknown. Here, we show that in living cells NF‐κB is immobilized onto high‐affinity binding sites only transiently, and that complete NF‐κB turnover on active chromatin occurs in less than 30 s. Therefore, promoter‐bound NF‐κB is in dynamic equilibrium with nucleoplasmic dimers; promoter occupancy and transcriptional activity oscillate synchronously with nucleoplasmic NF‐κB and independently of promoter occupancy by other sequence‐specific transcription factors. These data indicate that changes in the nuclear concentration of NF‐κB directly impact on promoter function and that promoters sample nucleoplasmic levels of NF‐κB over a timescale of seconds, thus rapidly re‐tuning their activity. We propose a revision of the enhanceosome concept in this dynamic framework.

CCL3 and CXCL12 regulate trafficking of mouse bone marrow NK cell subsets

Herein we have analyzed chemokine involvement in the trafficking of developing and mature mouse natural killer (NK) cells in the bone marrow (BM). We observed drastic changes of CCR1, CXCR3, and CXCR4 expression and function during progression from precursor NK (pNK) cells to immature DX5- NK (iNK) and mature DX5+ NK (mNK) cells. pNK and mNK cells expressed the 3 receptors, while only CXCR4 was detected on iNK cells. Correspondingly, mNK cells migrated to CXCL12, CXCL10, and CCL3, and pNK and iNK cells to CXCL12, whereas pNK cells migrated to CCL3 and CXCL10 only after CXCL12 stimulation. Comparison of BM, peripheral blood, and spleen mNK cell populations revealed that CXCL12, CXCL10, and CCL3 preferentially affected BM mNK cell migration. Administration of the CXCR4 antagonist, AMD-3100, to C57BL/6 mice induced strong reduction of mNK and iNK cells in the BM and increased their number in blood and spleen. Conversely, CCL3 administration selectively mobilized mNK cells from the BM and this effect correlated with its ability to inhibit CXCL12-mediated mNK cell responses in vitro. Our results suggest that the combined action of chemokines selectively regulates localization of NK cell subsets in the BM and direct their maturation and migration to the periphery.

Activin A induces dendritic cell migration through the polarized release of CXC chemokine ligands 12 and 14

Activin A is a dimeric protein, member of the transforming growth factor (TGF)-beta family that plays a crucial role in wound repair and in fetal tolerance. Emerging evidence also proposes activin A as a key mediator in inflammation. This study reports that activin A induces the directional migration of immature myeloid dendritic cells (iDCs) through the activation of ALK4 and ActRIIA receptor chains. Conversely, activin A was not active on plasmacytoid dendritic cells (DCs) or mature myeloid DCs. iDC migration to activin A was phosphatidylinositol 3-kinase gamma-dependent, Bordetella pertussis toxin- and cycloheximide-sensitive, and was inhibited by M3, a viral-encoded chemokine-binding protein. In a real-time video microscopy-based migration assay, activin A induced polarization of iDCs, but not migration. These characteristics clearly differentiated the chemotactic activities of activin A from TGF-beta and classic chemokines. By the use of combined pharmacologic and low-density microarray analysis, it was possible to define that activin-A-induced migration depends on the selective and polarized release of 2 chemokines, namely CXC chemokine ligands 12 and 14. This study extends the proinflammatory role of activin A to DC recruitment and provides a cautionary message about the reliability of the in vitro chemotaxis assays in discriminating direct versus indirect chemotactic agonists.

Type I interferons in systemic autoimmunity.

Type I IFN (IFN-I) was firstly described in 1957 as a soluble factor responsible for viral resistance in vitro. Today, it is well known that the IFN-I family comprises a wide number of cytokines with different modulatory effects on angiogenesis, cell growth, fibrosis, and apoptosis. However, one of the most important functions of IFN-I is the capability to trigger a complex array of cellular responses that result in a host-protective antiviral response. For this reason, IFN-I can be considered a “director” of protective immune responses. The recent finding of the so-called interferon signature in patients suffering from different autoimmune diseases has underlined its possible role in the pathogenesis of these diseases. On the other hand, IFN-α/β is reported to be efficacious in the treatment of some autoimmune and infectious diseases not responsive to conventional therapy. On these occasions, the treated patients often start or increase autoantibody production supporting the role of IFN as inducer of an autoimmune response. In this review, we will underline recent acquisitions about IFN-I biology, with a focus on the relevance of the induction of some autoimmune diseases, such as systemic lupus erythematosus, systemic sclerosis, rheumatoid arthritis, dermato/polymiositis, and Sjogrens syndrome.

Immune functions and recruitment of plasmacytoid dendritic cells in psoriasis

Psoriasis is one of the most common chronic T cell-mediated diseases in humans. Among the most proximal event in the innate immunity cascade driving psoriatic inflammation is the secretion of type I IFN by activated plasmacytoid dendritic cells (pDC), a special DC subset strategically positioned in pre-psoriatic symptomless skin. There is an IFN-α signature in primary psoriatic plaques, and blocking of type I IFN signalling can prevent the expansion of pathogenetic T cells and development of psoriatic phenotype. Recently, we have demonstrated that pDC infiltration in psoriatic skin correlates with the expression of markers typical of early phases of psoriasis, whereas it is almost absent in long-lasting lesions. Importantly, pDC recruitment in psoriatic skin is strictly associated with the chemerin/ChemR23 axis, and is temporally active during psoriatic plaque development. Pro-chemerin is produced primarily by dermal fibroblasts, but also by mast cells and endothelial cells. Once secreted, it can be activated by enzymes produced by neutrophils and mast cells, which infiltrate early psoriasis lesions. These findings propose the chemerin/ChemR23 axis as a potential novel therapeutic target in psoriasis.

Blocking TH17-polarizing cytokines by histone deacetylase inhibitors in vitro and in vivo

Histone deacetylase (HDAC) inhibitors are small molecules inducing cell‐cycle arrest, differentiation, and apoptosis, currently undergoing clinical trials as anticancer drugs. In addition, emerging evidence suggests HDAC inhibitors may have anti‐inflammatory and immunomodulatory properties as well, although the molecular mechanisms remain poorly defined. Given the central role of dendritic cells (DC) in the induction and maintenance of the inflammatory and immune response, we investigated the effects of HDAC inhibitors on the maturation and activation of human monocyte‐derived DC in the presence of LPS and IFN‐γ. Our results show that the production of TH1‐ and TH17‐inducing cytokines, namely IL‐12 and IL‐23, was inhibited by trichostatin A (72% and 52%, respectively) and suberoylanilide hydroxamic acid (86% and 83%). Strikingly, HDAC inhibitors were effective if added simultaneously as well as after the proinflammatory challenge, and their effect was not associated to a reduction of expression or function of LPS/IFN‐γ receptors. These findings were confirmed in two different murine models. In addition, HDAC inhibitors selectively blocked the production of TH1‐attracting chemokines CXCL9, CXCL10, and CXCL11. The reduction of TH1‐ and TH17‐inducing cytokines as well as TH1‐attracting chemokines may represent relevant mechanisms through which HDAC inhibitors at nonproapoptotic doses exert their immunomodulatory properties.

Identification of CXCL13 as a new marker for follicular dendritic cell sarcoma

The homeostatic chemokine CXCL13 is preferentially produced in B‐follicles and is crucial in the lymphoid organ development by attracting B‐lymphocytes that express its selective receptor CXCR5. Follicular dendritic cells (FDCs) have been identified as the main cellular source of this chemokine in lymphoid organs. Recently, genome‐wide approaches have suggested follicular CD4 T‐helper cells (THF) as additional CXCL13 producers in the germinal centre and the neoplastic counterpart of THF (CD4+ tumour T‐cells in angioimmunoblastic T‐cell lymphoma) retains the capability of producing this chemokine. In contrast, no data are available on CXCL13 expression on FDC sarcoma (FDC‐S) cells. By using multiple approaches, we investigated the expression of CXCL13 at mRNA and protein level in reactive and neoplastic FDCs. In reactive lymph nodes and tonsils, CXCL13 protein is mainly expressed by a subset of FDCs in B‐cell follicles. CXCL13 is maintained during FDC transformation, since both dysplastic FDCs from 13 cases of Castlemans disease and neoplastic FDCs from ten cases of FDC‐S strongly and diffusely express this chemokine. This observation was confirmed at mRNA level by using RT‐PCR and in situ hybridization. Of note, no CXCL13 reactivity was observed in a cohort of epithelial and mesenchymal neoplasms potentially mimicking FDC‐S. FDC‐S are commonly associated with a dense intratumoural inflammatory infiltrate and immunohistochemistry showed that these lymphocytes express the CXCL13 receptor CXCR5 and are mainly of mantle zone B‐cell derivation (IgD+ and TCL1+). In conclusion, this study demonstrates that CXCL13 is produced by dysplastic and neoplastic FDCs and can be instrumental in recruiting intratumoural CXCR5+ lymphocytes. In addition to the potential biological relevance of this expression, the use of reagents directed against CXCL13 can be useful to properly identify the origin of spindle cell and epithelioid neoplasms. Copyright

The Critical Role of IL-15 in the Antitumor Effects Mediated by the Combination Therapy Imatinib and IL-2

The synergistic antitumor effects of the combination therapy imatinib mesylate (IM) and IL-2 depended upon NK1.1- expressing cells and were associated with the accumulation of CD11cintB220+NK1.1+ IFN-producing killer dendritic cells (IKDC) into tumor beds. In this study, we show that the antitumor efficacy of the combination therapy was compromised in IL-15 and IFN-type 1R loss-of-function mice. IL-15Rα was required for the proliferation of IKDC during IM plus IL-2 therapy. Trans-presentation of IL-15/IL-15Rα activated IKDC to express CCR2 and to respond to type 1 IFN by producing CCL2. Moreover, the antitumor effects of the combination therapy correlated with a CCL2-dependent recruitment of IKDC, but not B220− NK cells, into tumor beds. Altogether, the IL-15-driven peripheral expansion and the CCL-2-dependent intratumoral chemoattraction of IKDC are two critical parameters dictating the antitumor efficacy of IM plus IL-2 in mice.