Francesco Sinigaglia

Inhibition of IL-12 production by 1,25-dihydroxyvitamin D3. Involvement of NF-kappaB downregulation in transcriptional repression of the p40 gene.

Interleukin 12 (IL-12), produced by myelomonocytic cells, plays a pivotal role in the development of T helper 1 (Th1) cells, which are involved in the pathogenesis of chronic inflammatory autoimmune disorders. 1,25-Dihydroxyvitamin D3 [1,25(OH)2D3] inhibits IL-12 production by activated macrophages and dendritic cells, thus providing a novel interpretation to its immunosuppressive properties. 1,25(OH)2D3 significantly inhibits mRNA expression for both IL-12 p35 and p40 subunits acting at the transcriptional level. The effect of 1,25(OH)2D3 on p40 promoter activation was analyzed by cotransfecting monocytic RAW264.7 cells with p40 promoter/reporter constructs and expression vectors for vitamin D3 receptor (VDR) and/or retinoid X receptor (RXRalpha). We observed transcriptional repression of the p40 gene by 1,25(OH)2D3, which required coexpression of VDR with RXR and an intact VDR DNA-binding domain. The repressive effect maps to a region in the p40 promoter containing a binding site for NF-kappaB (p40-kappaB). Deletion of the p40-kappaB site abrogates part of the inhibitory effect on the p40 promoter, confirming the functional relevance of this site. Activation of monocytic THP-1 cells in the presence of 1,25(OH)2D3 results in reduced binding to the p40-kappaB site. Thus, 1,25(OH)2D3 may negatively regulate IL-12 production by downregulation of NF-kappaB activation and binding to the p40-kappaB sequence.

Beta2-agonists prevent Th1 development by selective inhibition of interleukin 12.

Interleukin 12 (IL-12) plays a central role in the immune system by skewing the immune response towards T helper 1 (Th1) type responses which are characterized by high interferon-gamma and low IL-4 production. In this report we present evidence that beta2-agonists inhibit IL-12 production by both human monocytes in response to lipopolysaccharide (LPS) and dendritic cells stimulated via CD40. Inhibition of IL-12 production is selective, as other cytokines produced by monocytes are unaffected. IL-12 inhibition is dependent on beta2-adrenoceptor stimulation and correlates with increased levels of intracellular cAMP. In conjunction with their ability to suppress IL-12 production, when beta2-agonists are added at priming of neonatal T lymphocytes, they inhibit the development of Th1-type cells, while promoting T helper 2 (Th2) cell differentiation. Further, the in vivo administration of a therapeutic dose of salbutamol results in the selective inhibition of IL-12 production by whole blood lymphocytes stimulated in vitro with LPS. These findings provide new insight into the immunological consequences of the clinical use of beta2-agonists and may suggest new approaches for the treatment of Th1-mediated diseases.

The C-C chemokine receptors CCR4 and CCR8 identify airway T cells of allergen-challenged atopic asthmatics

In vitro polarized human Th2 cells preferentially express the chemokine receptors CCR3, CCR4, and CCR8 and migrate to their ligands: eotaxin, monocyte-derived chemokine (MDC), thymus- and activation-regulated chemokine (TARC), and I-309. We have studied the expression of chemokines and chemokine receptors in the airway mucosa of atopic asthmatics. Immunofluorescent analysis of endobronchial biopsies from six asthmatics, taken 24 hours after allergen challenge, demonstrates that virtually all T cells express IL-4 and CCR4. CCR8 is coexpressed with CCR4 on 28% of the T cells, while CCR3 is expressed on eosinophils but not on T cells. Expression of the CCR4-specific ligands MDC and TARC is strongly upregulated on airway epithelial cells upon allergen challenge, suggesting an involvement of this receptor/ligand axis in the regulation of lymphocyte recruitment into the asthmatic bronchi. In contrast to asthma, T cells infiltrating the airways of patients with chronic obstructive pulmonary disease and pulmonary sarcoidosis produce IFN-gamma and express high levels of CXCR3, while lacking CCR4 and CCR8 expression. These data support the role of CCR4, of its ligands MDC and TARC, and of CCR8 in the pathogenesis of allergen-induced late asthmatic responses and suggest that these molecules could be considered as targets for therapeutic intervention.

Promiscuous and allele-specific anchors in HLA-DR-binding peptides

The major histocompatibility complex (MHC) class II molecules are highly polymorphic membrane glycoproteins that bind peptide fragments of proteins and display them for recognition by CD4+ T cells. To understand the effect of human MHC class II polymorphism on peptide-MHC interaction, we have isolated M13 phage from a large M13 peptide display library by selection with DRB1*0401 and DRB1*1101 molecules, as recently described for DRB1*0101. Sequence analysis of the peptide-encoding region of DR-bound phage led to the identification of position-specific anchor residues, defining motifs for peptide binding to DR molecules. The three DR motifs share two anchor residues at relative positions 1 and 4, while allele-specific anchor residues have been identified at position 6. These results provide a biophysical basis for both the promiscuity and the specificity of peptide recognition by DR molecules.

Fractalkine (CX3CL1) as an amplification circuit of polarized Th1 responses

Fractalkine (FKN, CX3CL1) is a membrane-bound CX3C chemokine induced by primary proinflammatory signals in vascular endothelial cells (ECs). Here we examined the role of FKN in polarized Th1 or Th2 responses. Proinflammatory signals, including LPS, IL-1, TNF, and CD40 ligand, induced FKN, as did IFN-gamma, which had synergistic activity with TNF. IL-4 and IL-13 did not stimulate the expression of FKN and markedly reduced induction by TNF and IFN-gamma. TNF alone or combined with IFN-gamma also induced release of soluble FKN, which was inhibited by IL-4 and IL-13. In light of this differential regulation of FKN by the master cytokines that control polarized responses, we analyzed the interaction of FKN with natural killer (NK) cells and polarized T-cell populations. NK cells expressed high levels of the FKN receptor CX3CR1 and responded to FKN. CX3CR1 was preferentially expressed in Th1 compared with Th2 cells. Th1 but not Th2 cells responded to FKN. By immunohistochemistry, FKN was expressed on ECs in psoriasis, a Th1-dominated skin disorder, but not in Th2-driven atopic dermatitis. Similarly, ECs in Mycobacterium tuberculosis granulomatous lymphadenitis, but not those in reactive lymph node hyperplasia or in Castelmans disease, showed immunoreactive FKN. These results indicate that regulated expression of FKN in ECs participates in an amplification circuit of polarized type I responses.

Transcript imaging of the development of human T helper cells using oligonucleotide arrays.

Many pathological processes, including those causing allergies and autoimmune diseases, are associated with the presence of specialized subsets of T helper cells at the site of inflammation. Understanding the genetic program that controls the functional properties of T helper type 1 (Th1) versus T helper type 2 (Th2) cells may provide insight into the pathophysiology of inflammatory diseases. We compared the gene-expression profiles of human Th1 and Th2 cells using high-density oligonucleotide arrays with the capacity to display transcript levels of 6,000 human genes. Here we analyse the data sets derived from five independent experiments using statistical algorithms. This approach resulted in the identification of 215 differentially expressed genes, encoding proteins involved in transcriptional regulation, apoptosis, proteolysis, and cell adhesion and migration. A subset of these genes was further upregulated by exposure of differentiated Th1 cells to interleukin-12 (IL-12), as confirmed by kinetic PCR analysis, indicating that IL-12 modulates the effector functions of Th1 cells in the absence of antigenic stimulation. Functional assays and in vivo expression of selected genes have validated the biological relevance of our study. Our results provide new insight into the transcriptional program controlling the functional diversity of subsets of T helper cells.

Chemokine receptors in inflammation: an overview

Chemokine receptors play a key role in directing the migration of inflammatory cells into various injured or infected organs. However, migration of inflammatory cells into tissues can in itself be a cause and amplifier of tissue damage and disease, particularly in chronic autoimmune or allergic disorders. On this basis, much effort is currently devoted at the identification of molecular signals regulating the recruitment of inflammatory cells into tissues and at developing novel strategies to inhibit discrete pathways in this process. Great progress has recently been made in identification of a number of chemokine receptors involved in the process of leukocyte migration. The challenge is now to elucidate the specific contribution and involvement of the different receptors in distinct inflammatory processes and diseases and to prove that interference with any of these pathways may lead to development of novel therapeutics.

Regulation of the IL-12/IL-12R axis: a critical step in T-helper cell differentiation and effector function

Summary: Interleukin (IL)‐12 is required for the development of T‐helper (Th)1 cells, which have been shown to be important for protective cell‐mediated immune responses against a variety of intracellular pathogens. Recent studies have clarified the sources and the regulation ofIL‐12 production leading to Th1 development against microbes. Expression of IL‐12R is necessary for maintaining IL‐12 responsiveness and controlling Thl lineage commitment. Advances in this area have included a broader understanding of the factors involved in the regulation of the IL‐12Rβ2 signaling component. Expression of this receptor subunit in humans is critically influenced by IL‐12 and type I interferons. IL‐12 signaling results in STAT4 activation and interferon (IFN)‐γ production. Recent evidence suggests that IL‐12 also modulates a number of genes involved in leukocyte trafficking. Thus, IL‐12 is not only an important proinflammatory cytokine, which induces production of IFN‐γ and subsequent activation of phago‐cytic cells but also plays a major role in regulating the migration and proper positioning of effector cells.

Distribution and signaling of TREM2/DAP12, the receptor system mutated in human polycystic lipomembraneous osteodysplasia with sclerosing leukoencephalopathy dementia

Together with its adaptor protein, the adaptor protein of 12 kDa also known as KARAP and TYROBP (DAP12), triggering r (TREM2) is a stimulatory membrane receptor of the immunoglobulin/lectin‐like superfamily, well known in myeloid cells. In humans, however, loss‐of‐function mutations of TREM2/DAP12 leave myeloid cells unaffected but induce an autosomal recessive disease characterized, together with bone cysts, by a spectrum of pathological lesions in the cortex, thalamus and basal ganglia with clinical symptoms of progressive dementia (polycystic lipomembraneous osteodysplasia with sclerosing leukoencephalopathy). Nothing was known about the role of TREM2/DAP12 in brain cell biology and physiology. By confocal immunocytochemistry we demonstrate that, in both human and mouse cerebral cortex, TREM2/DAP12, strongly expressed by microglia, is also present in a fraction of neurons but not in astrocytes and oligodendrocytes. In contrast, in the hippocampal cortex TREM2‐expressing neurons are rare. Both in neurons and microglia the receptor appears to be located mostly intracellularly in a discrete compartment(s) partially coinciding with (or adjacent to) the Golgi complex/trans‐Golgi network. Four nerve cell lines were identified as expressing the intracellular receptor system. In living human microglia CHME‐5 and glioblastoma T98G cells, activation of TREM2 by its specific antibody induced [Ca2+]i responses, documenting its surface expression and functioning. Surface expression of TREM2, low in resting CHME‐5 and T98G cells, increases significantly and transiently (60 min) when cells are stimulated by ionomycin, as revealed by both surface biotinylation and surface immunolabeling. Our results provide the first information about the expression, distribution (mostly intracellular) and functioning of TREM2/DAP12 system in nerve cells, a necessary step in the understanding of the cellular mechanisms affected in polycystic lipomembraneous osteodysplasia with sclerosing leukoencephalopathy.

Differential regulation of chemokine production by Fcγ receptor engagement in human monocytes : association of CCL1 with a distinct form of M2 monocyte activation (M2b, Type 2)

CC chemokine ligand 1 (CCL1; I‐309) is a CC chemokine that interacts with CC chemokine receptor 8, which is preferentially expressed in polarized T helper cell type 2 and Tc2 cells, in eosinophils, and in T regulatory cells. The present study, prompted by transcriptional profiling of human monocytes undergoing different forms of activation, was designed to characterize the production of CCL1 in monocytes compared with the production of other chemokines (CCL2, CCL22, and CCL18) differentially regulated by distinct activation signals. Lipopolysaccharide (LPS), interferon‐γ (IFN‐γ), interleukin (IL)‐1β, tumor necrosis factor α, IL‐4, IL‐13, IL‐10, IL‐6, IL‐18, and combinations thereof did not induce CCL1 production in monocytes, and some of these signals stimulated production of reference chemokines. Induction of CCL1 in monocytes required engagement of Fc receptor for immunoglobulin G (FcγR)II and exposure to IL‐1β or LPS. This combination of stimuli results in a form of M2 (M2b, Type 2) macrophage activation. FcγR engagement also induced CCL22 and amplified its stimulation by IL‐4. In contrast, FcγR stimulation inhibited the IL‐10‐ and LPS‐mediated induction of CCL18. IL‐10, IL‐4, and IFN‐γ inhibited induction of CCL1 by FcγR ligation and IL‐1β. CCL1 was present in synovial fluids and macrophages in juvenile idiopathic arthritis. Thus, regulation of CCL1 in human monocytes is unique, with an obligate requirement of FcγR engagement and costimulation by signals (IL‐1β and LPS), which use the myeloid differentiation primary‐response protein 88 adaptor protein. Thus, CCL1 is a CC chemokine with a unique pattern of regulation associated with a distinct form of M2 (Type 2, M2b) monocyte activation, which participates in macrophage‐dependent regulatory circuits of innate and adaptive immunity.