Marika Sarfati

Thymic stromal lymphopoietin is released by human epithelial cells in response to microbes, trauma, or inflammation and potently activates mast cells

Compelling evidence suggests that the epithelial cell–derived cytokine thymic stromal lymphopoietin (TSLP) may initiate asthma or atopic dermatitis through a dendritic cell–mediated T helper (Th)2 response. Here, we describe how TSLP might initiate and aggravate allergic inflammation in the absence of T lymphocytes and immunoglobulin E antibodies via the innate immune system. We show that TSLP, synergistically with interleukin 1 and tumor necrosis factor, stimulates the production of high levels of Th2 cytokines by human mast cells (MCs). We next report that TSLP is released by primary epithelial cells in response to certain microbial products, physical injury, or inflammatory cytokines. Direct epithelial cell–mediated, TSLP-dependent activation of MCs may play a central role in “intrinsic” forms of atopic diseases and explain the aggravating role of infection and scratching in these diseases.

Common variants in the NLRP3 region contribute to Crohn's disease susceptibility

We used a candidate gene approach to identify a set of SNPs, located in a predicted regulatory region on chromosome 1q44 downstream of NLRP3 (previously known as CIAS1 and NALP3) that are associated with Crohns disease. The associations were consistently replicated in four sample sets from individuals of European descent. In the combined analysis of all samples (710 father-mother-child trios, 239 cases and 107 controls), these SNPs were strongly associated with risk of Crohns disease (Pcombined = 3.49 × 10−9, odds ratio = 1.78, confidence interval = 1.47–2.16 for rs10733113), reaching a level consistent with the stringent significance thresholds imposed by whole-genome association studies. In addition, we observed significant associations between SNPs in the associated regions and NLRP3 expression and IL-1β production. Mutations in NLRP3 are known to be responsible for three rare autoinflammatory disorders. These results suggest that the NLRP3 region is also implicated in the susceptibility of more common inflammatory diseases such as Crohns disease.

Bidirectional Negative Regulation of Human T and Dendritic Cells by CD47 and Its Cognate Receptor Signal-Regulator Protein-α: Down-Regulation of IL-12 Responsiveness and Inhibition of Dendritic Cell Activation

Proinflammatory molecules, including IFN-γ and IL-12, play a crucial role in the elimination of causative agents. To allow healing, potent anti-inflammatory processes are required to down-regulate the inflammatory response. In this study, we first show that CD47/integrin-associated protein, a ubiquitous multispan transmembrane protein highly expressed on T cells, interacts with signal-regulator protein (SIRP)-α, an immunoreceptor tyrosine-based inhibition motif-containing molecule selectively expressed on myelomonocytic cells, and next demonstrate that this pair of molecules negatively regulates human T and dendritic cell (DC) function. CD47 ligation by CD47 mAb or L-SIRP-α transfectants inhibits IL-12R expression and down-regulates IL-12 responsiveness of activated CD4+ and CD8+ adult T cells without affecting their response to IL-2. Human CD47-Fc fusion protein binds SIRP-α expressed on immature DC and mature DC. SIRP-α engagement by CD47-Fc prevents the phenotypic and functional maturation of immature DC and still inhibits cytokine production by mature DC. Finally, in allogeneic MLR between mDC and naive T cells, CD47-Fc decreases IFN-γ production after priming and impairs the development of a Th1 response. Therefore, CD47 on T cells and its cognate receptor SIRP-α on DC define a novel regulatory pathway that may be involved in the maintenance of homeostasis by preventing the escalation of the inflammatory immune response.

Expression, Structure, and Function of the CD23 Antigen

Publisher Summary The chapter explains that the structure of CD23 predicts both a lectin activity and a role in cellular adhesion. However, this view requires more experimental support, and, moreover, the binding to IgE does not require carbohydrate interactions. Interestingly, all the well-documented functions of CD23 (antigen presentation, parasite killing, and mediator release) are IgE dependent whereas most of the functions ascribed to sCD23 are clearly IgE independent. A hallmark of the CD23 molecule is that this transmembrane glycoprotein is continuously cleaved into soluble fragments, referred to as soluble CD23 (sCD23) that are released in the extracellular fluid. Most intriguingly, the two forms of CD23 may have different and sometimes antagonistic functions. In humans, some sCD23 fragments retain the ability to bind to IgE and have therefore been named IgE-binding factors (IgE–BFs). Human CD23 is a single-chain 45-kDa glycoprotein; it contains one chain of N-linked carbohydrates of the complex type, several O-linked carbohydrates, and sialic acid residues. Immunoprecipitation studies using either anti-CD23 Mab orIgE reveal the presence of three components with masses of 60–95, 45, and 37 kDa. The high-molecular-weight component is because of the formation of aggregates of the 45-kDa molecules after solubilization of the cells. Indeed, the molecules of 45 and 60–95 kDa display identical peptide maps and they share several antigenic determinants. This chapter discusses the functions of membrane CD23 and soluble CD23. In healthy individuals the serum level of sCD23 remains stable over a long period of time, indicating that it is not affected by environmental factors. CD23 is found at low levels on the majority of mature resting B cells, and freshly isolated PBMCs express only type a CD23 mRNA.

Maturation of human neonatal CD4+ and CD8+ T lymphocytes into Th1/Th2 effectors

The increased susceptibility of neonates to infections has been ascribed to the immaturity of their immune system. More particularly, T cell-dependent responses were shown to be biased towards a Th2 phenotype. Our studies on the in vitro maturation of umbilical cord blood T cells suggest that the Th2 bias of neonatal response cannot be simply ascribed to intrinsic properties of neonatal T cells. Phenotypically, neonatal CD4+ T cells are more immature than their adult CD45RO-/RA+ naive counterparts and they contain a subset (10-20%) of CD45RO-/RA+ CD31- cells which is very low in adults and displays some unique functional features. The activation and maturation of neonatal CD4+ T cells is particularly dependent upon the strength of CD28-mediated cosignal which dictates not only the cytokine profile released upon primary activation but also the response to IL-12. Activation of adult as well as neonatal CD4+ T cells in the context of low CD28 costimulation yields to the production of low levels of only one cytokine, i.e. IL-2. In contrast, strong CD28 costimulation supports the production of high levels of type 1 (IL-2, IFN gamma and TNF beta) and low levels of type 2 (IL-4 and IL-13) cytokines by neonatal T cells. The low levels of naive T cell-derived IL-4 are sufficient to support their development into high IL-4/IL-5 producers by an autocrine pathway. The ability of IL-12 to prime neonatal CD4+ T cells for increased production of IL-4 (in addition to IFN gamma) is observed only when CD28 cosignal is minimal. Under optimal activation conditions (i.e. with anti-CD3/B7.1 or allogenic dendritic cells) the response and the maturation of neonatal and adult naive T cells are similar. Thus the Th2 bias of neonatal immune response cannot be simply ascribed to obvious intrinsic T cell defect but rather to particular conditions of Ag presentation at priming. Unlike CD4+ T cells, neonatal CD8+ T cells strictly require exogenous IL-4 to develop into IL-4/IL-5 producers. Most importantly, anti-CD3/B7-activated neonatal CD8 T cells coexpress CD4 as well as CCR5 and CXCR4 and are susceptible to HIV-1 infection in vitro.

Thrombospondin 1 Is an Autocrine Negative Regulator of Human Dendritic Cell Activation

Thrombospondin 1 (TSP) elicits potent antiinflammatory activities in vivo, as evidenced by persistent, multiorgan inflammation in TSP null mice. Herein, we report that DCs represent an abundant source of TSP at steady state and during activation. Human monocyte-derived immature dendritic cells (iDCs) spontaneously produce TSP, which is strongly enhanced by PGE2 and to a lesser extent by transforming growth factor (TGF) β, two soluble mediators secreted by macrophages after engulfment of damaged tissues. Shortly after activation via danger signals, DCs transiently produce interleukin (IL) 12 and tumor necrosis factor (TNF) α, thereby eliciting protective and inflammatory immune responses. Microbial stimuli increase TSP production, which is further enhanced by IL-10 or TGF-β. The endogenous TSP produced during early DC activation negatively regulates IL-12, TNF-α, and IL-10 release through its interactions with CD47 and CD36. After prolonged activation, DCs extinguish their cytokine synthesis and become refractory to subsequent stimulation, thereby favoring the return to steady state. Such “exhausted” DCs continue to release TSP but not IL-10. Disrupting TSP–CD47 interactions during their restimulation restores their cytokine production. We conclude that DC-derived TSP serves as a previously unappreciated negative regulator contributing to arrest of cytokine production, further supporting its fundamental role in vivo in the active resolution of inflammation and maintenance of steady state.

Cloning and expression of the cDNA coding for a human lymphocyte IgE receptor.

Low‐affinity receptors (Fc epsilon R) and secreted factors (IgE‐BF) which bind to immunoglobulins of the IgE isotype play a key role in the regulation of human IgE synthesis. We report here the cloning of a cDNA coding for the Fc epsilon R of the human B‐lymphoblast cell line RPMI 8866. The nucleotide sequence of this cDNA predicts a polypeptide with 321 amino acids and a mol. wt of 36,281 daltons. A functional Fc epsilon R capable of binding IgE was expressed in Chinese hamster ovary cells after stable transformation with the cDNA which had been cloned into a mammalian expression vector. Amino acid sequence analysis of IgE‐BF purified from RPMI 8866 cells revealed an amino‐terminal sequence of 19 residues which coincides with the predicted amino acid sequence of the Fc epsilon R, starting at residues 148 and 150. A computer search with the translated amino acid sequence of the Fc epsilon R revealed a domain of 120 amino acids having striking homology to the human asialoglycoprotein receptors.

CD47 Engagement Inhibits Cytokine Production and Maturation of Human Dendritic Cells.

Upon encounter with bacterial products, immature dendritic cells (iDCs) release proinflammatory cytokines and develop into highly stimulatory mature DCs. In the present study, we show that human monocyte-derived DCs functionally express the CD47 Ag, a thrombospondin receptor. Intact or F(ab′)2 of CD47 mAb suppress bacteria-induced production of IL-12, TNF-α, GM-CSF, and IL-6 by iDCs. 4N1K, a peptide derived from the CD47-binding site of thrombospondin, also inhibits cytokine release. The inhibition of IL-12 and TNF-α is IL-10-independent inasmuch as IL-10 production is down-modulated by CD47 mAb and blocking IL-10 mAb fails to restore cytokine levels. CD47 ligation counteracts the phenotypic and functional maturation of iDCs in that it prevents the up-regulation of costimulatory molecules, the loss of endocytic activity, and the acquisition of an increased capacity to stimulate T cell proliferation and IFN-γ production. Interestingly, regardless of CD47 mAb treatment during DC maturation, mature DC restimulated by soluble CD40 ligand and IFN-γ, to mimic DC/T interaction, produce less IL-12 and more IL-18 than iDCs. Finally, CD47 ligation on iDCs does not impair their capacity to phagocytose apoptotic cells. We conclude that following exposure to microorganisms, CD47 ligation may limit the intensity and duration of the inflammatory response by preventing inflammatory cytokine production by iDCs and favoring their maintenance in an immature state.

Thrombospondin/CD47 Interaction: A Pathway to Generate Regulatory T Cells from Human CD4+CD25− T Cells in Response to Inflammation

Thymus-derived CD4+ CD25+ T regulatory cells (Tregs) are essential for the maintenance of self-tolerance. What critical factors and conditions are required for the extra-thymic development of Tregs remains an important question. In this study, we show that the anti-inflammatory extracellular matrix protein, thrombospondin-1, promoted the generation of human peripheral regulatory T cells through the ligation of one of its receptor, CD47. CD47 stimulation by mAb or a thrombospondin-1 peptide induced naive or memory CD4+CD25− T cells to become suppressive. The latter expressed increased amounts of CTLA-4, OX40, GITR, and Foxp3 and inhibited autologous Th0, Th1, and Th2 cells. Their regulatory activity was contact dependent, TGF-β independent, and partially circumvented by IL-2. This previously unknown mechanism to induce human peripheral Tregs in response to inflammation may participate to the limitation of collateral damage induced by exacerbated responses to self or foreign Ags and thus be relevant for therapeutic intervention in autoimmune diseases and transplantation.

Type I interferon restricts type 2 immunopathology through the regulation of group 2 innate lymphoid cells

Viral respiratory tract infections are the main causative agents of the onset of infection-induced asthma and asthma exacerbations that remain mechanistically unexplained. Here we found that deficiency in signaling via type I interferon receptor led to deregulated activation of group 2 innate lymphoid cells (ILC2 cells) and infection-associated type 2 immunopathology. Type I interferons directly and negatively regulated mouse and human ILC2 cells in a manner dependent on the transcriptional activator ISGF3 that led to altered cytokine production, cell proliferation and increased cell death. In addition, interferon-γ (IFN-γ) and interleukin 27 (IL-27) altered ILC2 function dependent on the transcription factor STAT1. These results demonstrate that type I and type II interferons, together with IL-27, regulate ILC2 cells to restrict type 2 immunopathology.