IL-33, an Interleukin-1-like Cytokine that Signals via the IL-1 Receptor-Related Protein ST2 and Induces T Helper Type 2-Associated Cytokines

Cytokines of the interleukin-1 (IL-1) family, such as IL-1 alpha/beta and IL-18, have important functions in host defense, immune regulation, and inflammation. Insight into their biological functions has led to novel therapeutic approaches to treat human inflammatory diseases. Within the IL-1 family, IL-1 alpha/beta, IL-1Ra, and IL-18 have been matched to their respective receptor complexes and have been shown to have distinct biological functions. The most prominent orphan IL-1 receptor is ST 2. This receptor has been described as a negative regulator of Toll-like receptor-IL-1 receptor signaling, but it also functions as an important effector molecule of T helper type 2 responses. We report a member of the IL-1 family, IL-33, which mediates its biological effects via IL-1 receptor ST 2, activates NF-kappaB and MAP kinases, and drives production of T(H)2-associated cytokines from in vitro polarized T(H)2 cells. In vivo, IL-33 induces the expression of IL-4, IL-5, and IL-13 and leads to severe pathological changes in mucosal organs.

New IL-17 family members promote Th1 or Th2 responses in the lung: in vivo function of the novel cytokine IL-25

We have biologically characterized two new members of the IL-17 cytokine family: IL-17F and IL-25. In contrast to conventional in vitro screening approaches, we have characterized the activity of these new molecules by direct in vivo analysis and have compared their function to that of other IL-17 family members. Intranasal administration of adenovirus expressing IL-17, IL-17C, or IL-17F resulted in bronchoalveolar lavage neutrophilia and inflammatory gene expression in the lung. In contrast, intranasal administration of IL-25-expressing adenovirus or IL-25 protein resulted in the production of IL-4, IL-5, IL-13, and eotaxin mRNA in the lung and marked eosinophilia in the bronchoalveolar lavage and lung tissue. Mice given intranasal IL-25 also developed epithelial cell hyperplasia, increased mucus secretion, and airway hyperreactivity. IL-25 gene expression was detected following Aspergillus and Nippostrongylus infection in the lung and gut, respectively. IL-25-induced eosinophilia required IL-5 and IL-13, but not IL-4 or T cells. Following IL-25 administration, the IL-5(+) staining cells were CD45R/B220(+), Thy-1(+/-), but were NK1.1-, Ly-6G(GR-1)-, CD4-, CD3-, and c-kit-negative. gamma-common knockout mice did not develop eosinophilia in response to IL-25, nor were IL-5(+) cells detected. These findings suggest the existence of a previously unrecognized cell population that may initiate Th2-like responses by responding to IL-25 in vivo. Further, these data demonstrate the heterogeneity of function within the IL-17 cytokine family and suggest that IL-25 may be an important mediator of allergic disease via production of IL-4, IL-5, IL-13, and eotaxin.

IL-25 induces IL-4, IL-5, and IL-13 and Th2-associated pathologies in vivo

We have characterized a cytokine produced by Th2 cells, designated as IL-25. Infusion of mice with IL-25 induced IL-4, IL-5, and IL-13 gene expression. The induction of these cytokines resulted in Th2-like responses marked by increased serum IgE, IgG(1), and IgA levels, blood eosinophilia, and pathological changes in the lungs and digestive tract that included eosinophilic infiltrates, increased mucus production, and epithelial cell hyperplasia/hypertrophy. In addition, our studies show that IL-25 induces Th2-type cytokine production by accessory cells that are MHC class II(high), CD11c(dull), and lineage(-). These results suggest that IL-25, derived from Th2 T cells, is capable of amplifying allergic type inflammatory responses by its actions on other cell types.

Immature human dendritic cells express asialoglycoprotein receptor isoforms for efficient receptor-mediated endocytosis

In a search for genes expressed by dendritic cells (DC), we have cloned cDNAs encoding different forms of an asialoglycoprotein receptor (ASGPR). The DC-ASGPR represents long and short isoforms of human macrophage lectin, a Ca(2+)-dependent type II transmembrane lectin displaying considerable homology with the H1 and H2 subunits of the hepatic ASGPR. Immunoprecipitation from DC using an anti-DC-ASGPR mAb yielded a major 40-kDa protein with an isoelectric point of 8.2. DC-ASGPR mRNA was observed predominantly in immune tissues. Both isoforms were detected in DC and granulocytes, but not in T, B, or NK cells, or monocytes. DC-ASGPR species were restricted to the CD14-derived DC obtained from CD34(+) progenitors, while absent from the CD1a-derived subset. Accordingly, both monocyte-derived DC and tonsillar interstitial-type DC expressed DC-ASGPR protein, while Langerhans-type cells did not. Furthermore, DC-ASGPR is a feature of immaturity, as expression was lost upon CD40 activation. In agreement with the presence of tyrosine-based and dileucine motifs in the intracytoplasmic domain, mAb against DC-ASGPR was rapidly internalized by DC at 37 degrees C. Finally, intracellular DC-ASGPR was localized to early endosomes, suggesting that the receptor recycles to the cell surface following internalization of ligand. Our findings identify DC-ASGPR/human macrophage lectin as a feature of immature DC, and as another lectin important for the specialized Ag-capture function of DC.

Autocatalytic activation of human legumain at aspartic acid residues

Human legumain was characterized following overexpression in a murine cell line as the C-terminal Ig-fusion protein. Upon acid treatment, the prolegumain autoproteolyzed distal to two aspartic acid residues to yield a highly active form. The ability of mature legumain to cleave after aspartic acid residues was confirmed with a small peptide substrate. Substitution of alanine for the putative catalytic cysteine, or for either of two strictly conserved histidine residues, partly or wholly eliminated autoactivation but not the ability of wild-type legumain to correctly process the variants to the properly sized proteins.

Impaired development of Th2 cells in IL-13-deficient mice

We report that Th2 cell cultures generated using T cells or splenocytes from IL-13-deficient mice produce significantly reduced levels of IL-4, IL-5, and IL-10 compared with wild-type. In contrast, IL-4 and IL-5 production by mast cells stimulated in vitro with PMA, ionomycin, or IgE cross-linking are unaffected. In vitro Th2 cell differentiation cannot be rescued by the addition of exogenous factors, but in vivo antigen challenge and administration of IL-13 can increase Th2-like cytokine responses as can infection with the parasitic nematode Nippostrongylus brasiliensis. IL-13-deficient mice also have lower basal levels of serum IgE and biased antigen-specific immunoglobulin responses. Thus, IL-13 is an important regulator of Th2 commitment and may therefore play a central role in atopy and infectious diseases.

Leukocystatin, a new Class II cystatin expressed selectively by hematopoietic cells

We describe a new cystatin in both mice and humans, which we termed leukocystatin. This protein has all the features of a Class II secreted inhibitory cystatin but contains lysine residues in the normally hydrophobic binding regions. As determined by cDNA library Southern blots, this cystatin is expressed selectively in hematopoietic cells, although fine details of the distribution among these cell types differ between the human and mouse mRNAs. In addition, we have determined the genomic organization of mouse leukocystatin, and we found that in contrast to most cystatins, the leukocystatin gene contains three introns. The recombinant proteins corresponding to these cystatins were expressed in Escherichia coli as N-terminal glutathione S-transferase or FLAGTM fusions, and studies showed that they inhibited papain and cathepsin L but with affinities lower than other cystatins. The unique features of leukocystatin suggests that this cystatin plays a role in immune regulation through inhibition of a unique target in the hematopoietic system.

Tumor necrosis factor alpha enhances the expression of the interleukin (IL)-4 receptor alpha-chain on endothelial cells increasing IL-4 or IL-13-induced Stat6 activation

Functional receptors for interleukin (IL)-4 and IL-13 on endothelial cells consist of the 130-kDa IL-4 receptor alpha-chain (IL-4Ralpha) and a 65-75-kDa IL-13 binding subunit that are expressed in a ratio of about 1:3, respectively. The restricted number of IL-4Ralpha limits subunit heterodimerization and in turn receptor-mediated signaling. We report here, the effects of tumor necrosis factor alpha (TNF-alpha) on the expression of the receptor subunits for IL-4 and IL-13. By flow cytofluorometry and receptor-binding analysis of iodinated IL-4 and IL-13, stimulation with TNF-alpha-induced a 2-3-fold increase of the IL-4Ralpha expression. The up-regulation was also confirmed at the transcriptional level by reverse transcription-polymerase chain reaction. Radioligand cross-linking experiments revealed no change in the subunit composition of the TNF-alpha-induced receptor complex. Nevertheless, TNF-alpha stimulation led to increased activation of the IL-4-specific signal transducers and activators of transcription protein (Stat6) by IL-4 and IL-13. Thus, TNF-alpha corrects the subunit imbalance of the endothelial IL-4.IL-13 receptor complex thereby increasing receptor heterodimerization and in turn the signaling capability by IL-4 and IL-13.

IL-4 induces human B cell maturation and IgE synthesis in SCID-hu mice. Inhibition of ongoing IgE production by in vivo treatment with an IL-4/IL-13 receptor antagonist

The effect of cytokine treatment on the in vivo maturation and Ig isotype switching of human B cells was studied in a modified SCID-hu mouse model. SCID mice, subcutaneously cotransplanted with small fragments of fetal human thymus and bone (SCID-hu BM/T mice) generated all human leukocyte lineages including T and B lymphocytes, macrophages, and granulocytes. All SCID-hu BM/T mice spontaneously produced human IgM and IgG, whereas IgE and IgA were detected in 37 and 80% of the mice, respectively, indicating that productive human T-B cell interactions resulting in Ig isotype switching occur in these mice. Administration of IL-4 to SCID-hu BM/T mice enhanced human B cell maturation, as judged by the increase in the percentages of CD45+, CD19+ bone marrow B cells expressing CD20, CD23, CD40, sIgM, and sIgD. Furthermore, these cells were also functionally more mature because they spontaneously produced human IgG/IgG4 in vitro and could be induced to secrete human IgE by addition of anti-CD40 mAb alone. In contrast, B cells isolated from PBS-treated mice only produced significant Ig levels after stimulation with anti-CD40 mAb in the presence of exogenous IL-4. IL-4 administration also induced human IgE synthesis in 44% of the mice, which had no serum IgE before treatment. More importantly, ongoing human IgE synthesis in SCID-hu BM/T mice was suppressed by > 90% following administration of an IL-4 mutant protein, which acts as an IL-4 and IL-13 receptor antagonist. These results suggest that IL-4/IL-13 receptor antagonists have potential clinical utility in treating human atopic diseases associated with enhanced IgE production.

Ligand binding kinetics of IL-2 and IL-15 to heteromers formed by extracellular domains of the three IL-2 receptor subunits

Studies on the binding of IL-2 to its receptor (IL-2R) have generally been limited to receptors expressed on cell surfaces. This has hampered detailed kinetic and mechanistic studies at the molecular level. We have prepared the soluble extracellular domains of all three receptor subunits (called alpha, beta and gamma) by recombinant techniques and have used these to perform detailed kinetic studies of their binding properties using the technique of surface plasmon resonance. We describe a novel approach whereby the receptors are assembled on an antibody surface, being held by an epitope engineered into the C-terminus of each of these domains. Thus the receptors are oriented naturally leading to homogeneous ligand binding kinetics. We have characterized the interactions of the heteromeric complexes of these subunits with mouse and human IL-2 and their analogs, as well as the recently discovered cytokine, IL-15. We have also studied the extracellular domains of the mouse receptor subunits for the first time and have used these as well as mouse-human hybrid receptors to probe the mechanism of assembly of these complexes. We show that no additional proteins are required to reproduce the properties of these complexes in vitro. In addition, kinetic studies with site-specific analogs of IL-2 and the mouse-human receptor hybrids clearly indicate that the extracellular domains of alpha and beta can together readily bind ligand with kinetic properties distinct from those of the constituent subunits. In contrast, a complex containing ligand and the extracellular domains of beta and gamma was comparatively difficult to assemble and required prolonged exposure to IL-2. Our method enabled us to calculate the stoichiometry of these complexes and to determine that anchoring these subunits is necessary to efficiently drive complex formation. The kinetic and equilibrium differences between the mouse and human receptor complexes, and between IL-2 and IL-15 binding to these receptors clarify the roles of the alpha and gamma subunits in the differential response of cells to different cytokines that may be present simultaneously in the environment.

IL-4 induces human B cell maturation and IgE synthesis in SCID-hu mice. Inhibition of ongoing IgE production by in vivo treatment with an IL-4/IL-13 receptor antagonist

The effect of cytokine treatment on the in vivo maturation and Ig isotype switching of human B cells was studied in a modified SCID-hu mouse model. SCID mice, subcutaneously cotransplanted with small fragments of fetal human thymus and bone (SCID-hu BM/T mice) generated all human leukocyte lineages including T and B lymphocytes, macrophages, and granulocytes. All SCID-hu BM/T mice spontaneously produced human IgM and IgG, whereas IgE and IgA were detected in 37 and 80% of the mice, respectively, indicating that productive human T-B cell interactions resulting in Ig isotype switching occur in these mice. Administration of IL-4 to SCID-hu BM/T mice enhanced human B cell maturation, as judged by the increase in the percentages of CD45+, CD19+ bone marrow B cells expressing CD20, CD23, CD40, sIgM, and sIgD. Furthermore, these cells were also functionally more mature because they spontaneously produced human IgG/IgG4 in vitro and could be induced to secrete human IgE by addition of anti-CD40 mAb alone. In contrast, B cells isolated from PBS-treated mice only produced significant Ig levels after stimulation with anti-CD40 mAb in the presence of exogenous IL-4. IL-4 administration also induced human IgE synthesis in 44% of the mice, which had no serum IgE before treatment. More importantly, ongoing human IgE synthesis in SCID-hu BM/T mice was suppressed by > 90% following administration of an IL-4 mutant protein, which acts as an IL-4 and IL-13 receptor antagonist. These results suggest that IL-4/IL-13 receptor antagonists have potential clinical utility in treating human atopic diseases associated with enhanced IgE production.

CD38-mediated ribosylation of proteins

The lymphocyte cell-surface Ag CD38 catabolizes NAD to adenosine 5' diphosphoribose (ADPR) and cyclic ADPR (cADPR). We show here that the soluble extracellular domain of CD38 (sCD38) mediates ADP ribosylation of several proteins. This was demonstrated by mass spectrometric analyses which revealed the addition of mass in units of 541.1 Da to these proteins, presumably corresponding to the covalent attachment of one or more ADPR moieties. Separate experiments showed that the same proteins became specifically radiolabeled following incubation with [32P]NAD plus sCD38. Additionally, it is shown that sCD38 can autoribosylate. Moreover, sCD38-mediated protein ribosylation was found to occur specifically at cysteine residues, since it was effectively blocked by addition of L-cysteine but not by other amino acids, and CD38-mediated protein ribosylation could be reversed by the addition of HgCl2, which specifically cleaves thiol-glycosidic bonds. ADPR purified from the reaction of sCD38 with NAD could itself be covalently transferred to target proteins at rates similar to the sCD38-mediated reaction, indicating that the ribosylation proceeds via the generation of this reactive intermediate. In vitro mutagenesis of a catalytic Glu residue that is conserved in numerous ADP-ribosyl transferases revealed that this amino acid is also important for catalysis in CD38. These data suggest that CD38 has the potential to cause ribosylation of experimental proteins, and raises the possibility that its specific ribosylation of a currently unidentified lymphocyte protein may contribute to its array of immunoregulatory activities.

CD38-mediated ribosylation of proteins

The lymphocyte cell-surface Ag CD38 catabolizes NAD to adenosine 5' diphosphoribose (ADPR) and cyclic ADPR (cADPR). We show here that the soluble extracellular domain of CD38 (sCD38) mediates ADP ribosylation of several proteins. This was demonstrated by mass spectrometric analyses which revealed the addition of mass in units of 541.1 Da to these proteins, presumably corresponding to the covalent attachment of one or more ADPR moieties. Separate experiments showed that the same proteins became specifically radiolabeled following incubation with [32P]NAD plus sCD38. Additionally, it is shown that sCD38 can autoribosylate. Moreover, sCD38-mediated protein ribosylation was found to occur specifically at cysteine residues, since it was effectively blocked by addition of L-cysteine but not by other amino acids, and CD38-mediated protein ribosylation could be reversed by the addition of HgCl2, which specifically cleaves thiol-glycosidic bonds. ADPR purified from the reaction of sCD38 with NAD could itself be covalently transferred to target proteins at rates similar to the sCD38-mediated reaction, indicating that the ribosylation proceeds via the generation of this reactive intermediate. In vitro mutagenesis of a catalytic Glu residue that is conserved in numerous ADP-ribosyl transferases revealed that this amino acid is also important for catalysis in CD38. These data suggest that CD38 has the potential to cause ribosylation of experimental proteins, and raises the possibility that its specific ribosylation of a currently unidentified lymphocyte protein may contribute to its array of immunoregulatory activities.

The primary binding subunit of the human interleukin-4 receptor is also a component of the interleukin-13 receptor

Interleukin (IL)-13 elicits a subset of the biological activities of the related IL-4. The basis of this functional similarity is that their specific cell-surface receptors (called IL-13R and IL-4R) are distinct, yet are complex and share a common subunit(s). The IL-4R primary binding subunit (called IL-4R alpha) does not by itself bind IL-13. We show that the ability of IL-13 to partially compete for IL-4 binding to some human cell types depended on co-expression of IL-4R and IL-13R. However, IL-13 binding was always associated with IL-4 binding. Hyper-expression of IL-4R alpha on cells expressing both IL-4R and IL-13R decreased their binding affinity for IL-4, abrogated the ability of IL-13 to compete for IL-4 binding, and yet had no effect on IL-13R properties. Anti-human IL-4R alpha monoclonal antibodies which blocked the biological function and binding of IL-4 also blocked the function and binding of IL-13. These data show that IL-4R alpha is a secondary component of IL-13R.

Immunoregulatory properties of IL-13: its potential role in atopic disease

IL-13 is a relatively novel cytokine produced by activated T cells. IL-13 inhibits the production of proinflammatory cytokines and chemokines by activated monocytes, induces B cell proliferation and differentiation, including IgE production, and the expression of certain adhesion molecules on endothelial cells. All these biological properties of IL-13 are shared with IL-4, but in contrast to IL-4, IL-13 does not act on T cells. In this review, the similarities in structure and biological function of IL-13 and IL-4 and the commonalities of their receptors are summarized. The potential role of IL-13 in allergic responses is briefly discussed.

IL-13 has only a subset of IL-4-like activities on B chronic lymphocytic leukaemia cells

The recently described interleukin-13 (IL-13) has been shown to share many of the effects of IL-4 on normal B cells, including growth-promoting activity and induction of CD23. In this study, we compared the effects of IL-13 and IL-4 on B chronic lymphocytic leukaemias (B-CLL) cells. After anti-CD40 activation, both IL-13 and IL-4 promoted the DNA synthesis of B-CLL cells and increased the recovery of viable cells. The time kinetics of the proliferative response of B-CLL cells to IL-13 or IL-4 were superimposable and showed the long-lasting effect of both cytokines. As on normal B cells, both IL-4 and IL-13 synergized with IL-10 to enhance B-CLL DNA synthesis. Moreover, IL-13, like IL-4, was able to increase CD23 expression on anti-CD40-activated leukaemic B cells. The CD23 up-regulation and the DNA synthesis induced by IL-13 on anti-CD40-activated B-CLL cells, were significantly reduced when B-CLL cells were cultured with anti-IL-4 receptor monoclonal antibody, suggesting a common pathway for IL-13 and IL-4 signalling. However, after cross-linking of surface IgM, IL-4 strongly inhibited the IL-2-induced DNA synthesis of B-CLL cells, whereas IL-13 did not inhibit IL-2-driven proliferation of anti-IgM-activated B-CLL cells. Furthermore, while IL-4 strongly up-regulated the expression of CD23 on anti-IgM-activated leukaemic B cells, IL-13 only marginally increased it. Finally, IL-13, in contrast to IL-4, did not prevent the entry of B-CLL cells into apoptosis. Thus IL-13 and IL-4 display comparable effects on anti-CD40-activated B-CLL cells, which are blocked by anti-IL-4 receptor (IL-4R) monoclonal antibodies. However, IL-13-dependent effects are absent or inefficient in non-activated or anti-IgM-activated B-CLL cells. This suggests that such cells may lack functional IL-13 receptors, though IL-13R and IL-4R on B-CLL cells share a common component.

Interleukin 13 elicits a subset of the activities of its close relative interleukin 4

Interleukin 13 (IL-13) and interleukin 4 (IL-4) are two closely related proteins produced by activated T cells. IL-4 is a well characterized mediator of various aspects of the immune response, including anti-inflammatory effects on monocytes and macrophages, regulation of B cell function, T cell growth, and regulation of adhesion molecule expression on endothelial cells. IL-13, a more recently characterized cytokine, appears to exhibit IL-4-like activities on monocytes, macrophages and human B cells, but has no effect on T cells. While there is a close parallel between IL-4 activities on human and mouse cells, IL-13 activities in these two systems appear to differ substantially with a notable absence of effect on mouse B cells. This review briefly summarizes the current state of knowledge of the interrelated activities of IL-13 and IL-4, explores the basis of these effects at the receptor level and attempts to rationalize the existence of these close relatives via differences in their production by T cells.

Embryonic implantation in mice is blocked by interleukin-1 receptor antagonist

We have investigated the relevance of interleukin-1 receptor type I (IL-1R tI) in the implantation process in vivo in a murine model. Indirect immunofluorescence experiments demonstrate that IL-1R tI is located in mouse endometrial lumenal epithelium with increased intensity in the periimplantation period, whereas IL-1 beta staining is located in the mouse placenta. PMSG/human CG (hCG)-stimulated and mated 12-week-old B6C3F-1 female mice were randomly allocated to three groups: A, control noninjected; B, buffer-injected animals; and C, animals injected ip with 20 micrograms recombinant human IL-1 receptor antagonist (rhIL-1ra) every 12 h beginning on pregnancy day 3. Injections were continued until day 9, and animals were killed 12 h after the last injection. Pregnancy rates in the three groups were: noninjected, 58.8% (10 of 17); buffer-injected, 73.7% (14 of 19); rhIL-1ra-injected, 6.7% (1 of 15), P = 0.0001155, Fisher exact test. To rule out the possibility that pregnancy failure was due to an embryotoxic effect of rhIL-1ra, 2-cell mouse embryos (n = 276) were flushed from the same group of animals used for in vivo experiments and cultured with increasing concentrations of rhIL-1ra: 0 microgram/ml (n = 91), 1 microgram/ml (n = 36), 50 micrograms/ml (n = 36), 100 micrograms/ml (n = 52), and 200 micrograms/ml (n = 61) rhIL-1ra. The percentages of 2-cell mouse embryos reaching the blastocyst stage after 72 h in culture were 85.7%, 91.6%, 94.4%, 96%, and 85.2%, respectively. We further cultured these blastocysts for 5 days on fibronectin-coated plates with or without 200 micrograms/ml rhIL-1ra. In both groups, hatching, attachment to fibronectin, outgrowth, and migration were documented to be similar. Furthermore, our longitudinal morphological study of embryonic implantation in control and rhIL-1ra-injected mice shows that the blockade of IL-1R tI interferes with the attachment of mouse blastocysts to maternal endometrium in vivo. In summary, we demonstrate that blockade of maternal endometrial IL-1R tI with IL-1ra prevents implantation in the mouse by interfering with embryonic attachment, without adverse effects on blastocyst formation, hatching, fibronectin attachment, outgrowth, and migration in vitro.