Cytokine receptors: structure and signal transduction

Balancing the Scales: The Dual Role of Interleukins in Bone Metastatic Microenvironments

Bone metastases, a common and debilitating consequence of advanced cancers, involve a complex interplay between malignant cells and the bone microenvironment. Central to this interaction are interleukins (ILs), a group of cytokines with critical roles in immune modulation and inflammation. This review explores the dualistic nature of pro-inflammatory and anti-inflammatory interleukins in bone metastases, emphasizing their molecular mechanisms, pathological impacts, and therapeutic potential. Pro-inflammatory interleukins, such as IL-1, IL-6, and IL-8, have been identified as key drivers in promoting osteoclastogenesis, tumor proliferation, and angiogenesis. These cytokines create a favorable environment for cancer cell survival and bone degradation, contributing to the progression of metastatic lesions. Conversely, anti-inflammatory interleukins, including IL-4, IL-10, and IL-13, exhibit protective roles by modulating immune responses and inhibiting osteoclast activity. Understanding these opposing effects is crucial for developing targeted therapies aimed at disrupting the pathological processes in bone metastases. Key signaling pathways, including NF-κB, JAK/STAT, and MAPK, mediate the actions of these interleukins, influencing tumor cell survival, immune cell recruitment, and bone remodeling. Targeting these pathways presents promising therapeutic avenues. Current treatment strategies, such as the use of denosumab, tocilizumab, and emerging agents like bimekizumab and ANV419, highlight the potential of interleukin-targeted therapies in mitigating bone metastases. However, challenges such as therapeutic resistance, side effects, and long-term efficacy remain significant hurdles. This review also addresses the potential of interleukins as diagnostic and prognostic biomarkers, offering insights into patient stratification and personalized treatment approaches. Interleukins have multifaceted roles that depend on the context, including the environment, cell types, and cellular interactions. Despite substantial progress, gaps in research persist, particularly regarding the precise mechanisms by which interleukins influence the bone metastatic niche and their broader clinical implications. While not exhaustive, this overview underscores the critical roles of interleukins in bone metastases and highlights the need for continued research to fully elucidate their complex interactions and therapeutic potential. Addressing these gaps will be essential for advancing our understanding and treatment of bone metastases in cancer patients.

AlphaFold2 enables accurate deorphanization of ligands to single-pass receptors

Secreted proteins play crucial roles in paracrine and endocrine signaling; however, identifying novel ligand-receptor interactions remains challenging. Here, we benchmarked AlphaFold as a screening approach to identify extracellular ligand-binding pairs using a structural library of single-pass transmembrane receptors. Key to the approach is the optimization of AlphaFold input and output for screening ligands against receptors to predict the most probable ligand-receptor interactions. Importantly, the predictions were performed on ligand-receptor pairs not used for AlphaFold training. We demonstrate high discriminatory power and a success rate of close to 90 % for known ligand-receptor pairs and 50 % for a diverse set of experimentally validated interactions. These results demonstrate proof-of-concept of a rapid and accurate screening platform to predict high-confidence cell-surface receptors for a diverse set of ligands by structural binding prediction, with potentially wide applicability for the understanding of cell-cell communication.

JAK-STAT pathway inhibitors in dermatology

The JAK-STAT signaling pathway mediates important cellular processes such as immune response, carcinogenesis, cell differentiation, division and death. Therefore, drugs that interfere with different JAK-STAT signaling patterns have potential indications for various medical conditions. The main dermatological targets of JAK-STAT pathway inhibitors are inflammatory or autoimmune diseases such as psoriasis, vitiligo, atopic dermatitis and alopecia areata; however, several dermatoses are under investigation to expand this list of indications. As JAK-STAT pathway inhibitors should gradually occupy a relevant space in dermatological prescriptions, this review presents the main available drugs, their immunological effects, and their pharmacological characteristics, related to clinical efficacy and safety, aiming to validate the best dermatological practice.

Role of Innate and Adaptive Cytokines in the Survival of COVID-19 Patients

SARS-CoV-2 is a new coronavirus characterized by a high infection and transmission capacity. A significant number of patients develop inadequate immune responses that produce massive releases of cytokines that compromise their survival. Soluble factors are clinically and pathologically relevant in COVID-19 survival but remain only partially characterized. The objective of this work was to simultaneously study 62 circulating soluble factors, including innate and adaptive cytokines and their soluble receptors, chemokines and growth and wound-healing/repair factors, in severe COVID-19 patients who survived compared to those with fatal outcomes. Serum samples were obtained from 286 COVID-19 patients and 40 healthy controls. The 62 circulating soluble factors were quantified using a Luminex Milliplex assay. Results. The patients who survived had decreased levels of the following 30 soluble factors of the 62 studied compared to those with fatal outcomes, therefore, these decreases were observed for cytokines and receptors predominantly produced by the innate immune system—IL-1α, IL-1α, IL-18, IL-15, IL-12p40, IL-6, IL-27, IL-1Ra, IL-1RI, IL-1RII, TNFα, TGFα, IL-10, sRAGE, sTNF-RI and sTNF-RII—for the chemokines IL-8, IP-10, MCP-1, MCP-3, MIG and fractalkine; for the growth factors M-CSF and the soluble receptor sIL2Ra; for the cytokines involved in the adaptive immune system IFNγ, IL-17 and sIL-4R; and for the wound-repair factor FGF2. On the other hand, the patients who survived had elevated levels of the soluble factors TNFβ, sCD40L, MDC, RANTES, G-CSF, GM-CSF, EGF, PDGFAA and PDGFABBB compared to those who died. Conclusions. Increases in the circulating levels of the sCD40L cytokine; MDC and RANTES chemokines; the G-CSF and GM-CSF growth factors, EGF, PDGFAA and PDGFABBB; and tissue-repair factors are strongly associated with survival. By contrast, large increases in IL-15, IL-6, IL-18, IL-27 and IL-10; the sIL-1RI, sIL1RII and sTNF-RII receptors; the MCP3, IL-8, MIG and IP-10 chemokines; the M-CSF and sIL-2Ra growth factors; and the wound-healing factor FGF2 favor fatal outcomes of the disease.

Effect of SXWS/WSXWS peptides on chemotaxis and adhesion of the macrophage-like cell line J774

WSXWS motif is a conserved amino acid sequence that is present in type I cytokine receptors. This motif that can be found both in the ligand binding chains and signal transducer molecule of the receptors with different amino acids at the position "X" plays a role in the receptor folding, ligand binding and signal transduction as well. Structural analysis proved that WSEWS motif of IL-6R is located in a highly accessible location in the protein. Structural properties and chemotaxis of a tetrapeptide library with SXWS sequence, where X was the 19 proteinogenic amino acids except cystein were systematically studied earlier. It has been proved that C-terminal amidation and the identity of amino acid X had a pronounced influence on the chemotactic properties but less of the structure of the peptides. Here, we present our findings on the effect of a tetrapeptide and a pentapeptide library with the sequence of SXWS and WSXWS on the chemotaxis and adhesion of J774 murine macrophage cell line. We studied the effect of the presence/absence of N-terminal tryptophan and the different amino acids at the X position on these physiological responses. Results indicated that amino acid X had a marked influence on chemotaxis, adhesion as well as on proliferation induced by (W)SXWS peptides. Elongation of SXWS sequence with a tryptophan at the N terminus also altered pronouncedly all the physiological responses of the cells studied. A good correlation could be observed between the chemotaxis and the proliferation and physicochemical parameters of the amino acid X.

The erythropoietin receptor: molecular structure and hematopoietic signaling pathways

The process of erythropoiesis in the fetal liver and adult bone marrow is regulated by the hormone erythropoietin (Epo), which is produced in the kidney at low levels under homeostatic conditions. Defects in Epo production result in severe anemia; use of recombinant hormone has improved the lives of patients with renal failure or anemia because of bone marrow suppression. Deletion of the Epo gene in mice leads to embryonic lethality at days 13 to 15, coincident with the establishment of definitive (adult-type) erythropoiesis and underscoring the absolute necessity of Epo function in vivo. Epo has proven to be a successful pharmaceutical agent, one of the early triumphs of recombinant protein technology. Because of its clinical importance, a great deal of attention has focused on the molecular mechanisms of Epo-regulated erythropoiesis. This review highlights the basic concepts of Epo signal transduction within the hematopoietic system, the major site of Epo action in vivo.

The erythropoietin receptor: molecular structure and hematopoietic signaling pathways

The process of erythropoiesis in the fetal liver and adult bone marrow is regulated by the hormone erythropoietin (Epo), which is produced in the kidney at low levels under homeostatic conditions. Defects in Epo production result in severe anemia; use of recombinant hormone has improved the lives of patients with renal failure or anemia because of bone marrow suppression. Deletion of the Epo gene in mice leads to embryonic lethality at days 13 to 15, coincident with the establishment of definitive (adult-type) erythropoiesis and underscoring the absolute necessity of Epo function in vivo. Epo has proven to be a successful pharmaceutical agent, one of the early triumphs of recombinant protein technology. Because of its clinical importance, a great deal of attention has focused on the molecular mechanisms of Epo-regulated erythropoiesis. This review highlights the basic concepts of Epo signal transduction within the hematopoietic system, the major site of Epo action in vivo.

Characterization of kinase inhibitors using reverse phase protein arrays

Using the reverse protein array platform in combination with planar waveguide technology, which allows detection of proteins in spotted cell lysates with high sensitivity in a 96-well microtiter-plate format for growing, treating, and lysing cells was shown to be suitable for this approach and indicates the usefulness of the technology as a screening tool for characterization of large numbers of kinase inhibitors. In this study, we have used reverse protein arrays to profile kinase inhibitors in various cellular pathways in order to unravel their MoA. Multiplexing and simultaneous analysis of several phospho-proteins within the same lysate allows (1) the estimation of inhibitor concentrations needed to shut down an entire pathway, (2) the estimation of inhibitor selectivity, and (3) the comparison of inhibitors of different kinases within one assay. For example, parallel analysis of p-InsR, p-PKB, p-GSK-3, p-MEK, p-ERK, and p-S6rp in insulin treated A14 cells allows profiling for inhibitors of the InsR, PI3K, PKB, mTor, RAF, and MEK. Selective kinase inhibitors revealed different specific inhibitory pattern of the analyzed phospho-read outs. Altogether, multiplexed analysis of reverse (phase) protein arrays is a powerful tool to characterize kinase inhibitors in a semi-automated low to medium throughput assay format.

Molecular mechanisms of IFN-gamma to up-regulate MHC class I antigen processing and presentation

IFN-gamma up-regulates MHC class I expression and antigen processing and presentation on cells, since IFN-gamma can induce multiple gene expressions that are related to MHC class I antigen processing and presentation. MHC class I antigen presentation-associated gene expression is initiated by IRF-1. IRF-1 expression is initiated by phosphorylated STAT1. IFN-gamma binds to IFN receptors, and then activates JAK1/JAK2/STAT1 signal transduction via phosphorylation of JAK and STAT1 in cells. IFN-gamma up-regulates MHC class I antigen presentation via activation of JAK/STAT1 signal transduction pathway. Mechanisms of IFN-gamma to enhance MHC class I antigen processing and presentation were summarized in this literature review.

A form of circulating interleukin-6 receptor component soluble gp130 as a potential interleukin-6 inhibitor in inflammatory bowel disease

The presence and the role of soluble gp130, the soluble form of a component of the interleukin (IL)-6 receptor complex, were investigated in inflammatory bowel disease. The serum concentrations of soluble gp130 were increased in ulcerative colitis (active disease, median, 93.5 ng/ml; interquartile range, 26-125 ng/ml; inactive disease, 81 ng/ml, 24.8-137.3 ng/ml) and to a lesser extent in Crohn's disease (active disease, 66 ng/ml, 44.4-87.6 ng/ml; inactive disease, 63 ng/ml, 43.5-82.5 ng/ml) compared to normal controls (43 ng/ml, 27-59 ng/ml). Paired analysis of serum samples showed a decrease of IL-6 and soluble IL-6 receptor concentrations in both diseases and an increase of soluble gp130 concentrations, especially in ulcerative colitis, just after the resolution of disease exacerbation. Size fractionation of the serum revealed that a part of the IL-6 co-eluted with soluble gp130 and soluble IL-6 receptor. The IL-6-induced proliferation of murine B9 hybridoma was enhanced by recombinant soluble IL-6 receptor, whereas the proliferation was inhibited by recombinant soluble gp130. These results indicate that soluble gp130 may function as a natural inhibitor of the IL-6 actions in inflammatory bowel disease.

The role of tumor necrosis factor in cardiac disease

Tumor necrosis factor (TNF) is a proinflammatory cytokine that can produce widespread deleterious effects when expressed in large amounts. It is produced in the heart by both cardiac myocytes and resident macrophages under conditions of cardiac stress, and is thought to be responsible for many of the untoward manifestations of cardiac disease. This article discusses the role of TNF in heart disease and some potential therapeutic modalities that can influence the cytokine activity. The results of controlled studies would suggest that TNF inhibition does not influence the clinical course of patients with heart failure.

Low-affinity nerve growth factor receptor (p75) in dermatofibrosarcoma protuberans and other nonneural tumors: a study of 1,150 tumors and fetal and adult normal tissues

Low-affinity nerve growth factor receptor (p75) is a member of the tumor necrosis factor receptor family. It may modulate the binding of nerve growth factor (NGF) to the functional high-affinity receptor tyrosine kinase (trk) A. NGF is thought to be responsible for growth, apoptosis, and function of the nervous system. The presence of this receptor (p75) was determined in a large group of neural and nonneural tumors and fetal and adult tissues. One thousand one hundred fifty tumors were analyzed with monoclonal antibody for p75, along with selected normal fetal and adult tissues. Immunoreactivity for p75 was present in adult pericytes, perivascular fibroblasts, basal cells of several types of epithelia, perineurial cells, and dendritic reticulum cells. Additionally, a wide zone of subepithelial mesenchyme and skeletal muscle were positive in the first-trimester fetus, but were diminished or negative in the adult. Consistently positive nonneural mesenchymal tumors included dermatofibrosarcoma protuberans (DFSP), embryonal and alveolar rhabdomyosarcoma, synovial sarcoma, and spindle cell hemangio(endotheli)oma. Schwann cell tumors, ganglioneuroma, granular cell tumor, and malignant peripheral nerve sheath tumor (MPNST) were also p75 positive. Mesenchymal nonneural tumors that were variably positive (32% to 69%) for p75 included fibrosarcoma variants, solitary fibrous tumor, hemangiopericytoma, spindle cell lipoma, Ewing's sarcoma, mesenchymal chondrosarcoma, and malignant melanoma. Nervous system tumors such as paragangliomas, neuroblastoma, meningioma, and perineurioma and nonneural mesenchymal tumors, including extraskeletal osteosarcoma, benign fibrous histiocytomas, fibromas, alveolar soft part sarcoma, epithelioid sarcoma, smooth muscle and gastrointestinal stromal tumors, and angiosarcomas, were almost always negative for p75. Epithelial tumors that were consistently positive included mixed tumor and adenoid cystic carcinoma, whereas mesothelioma, adenocarcinomas, and most squamous cell carcinomas were negative. p75 is not a specific marker for nerve sheath tumors. It is present in a variety of other mesenchymal tumors including synovial sarcoma and in CD34-positive tumors such as DFSP, spindle cell lipoma, and hemangiopericytoma. The presence of p75 in nonneural tumors such as DFSP and rhabdomyosarcoma mimic its presence in early fetal mesenchyme and skeletal muscle, suggesting oncofetal expression in these tumors. p75 may be useful to distinguish DFSP from benign fibrous histiocytoma.

Complex interactions between sex steroids and cytokines in the human pregnant myometrium: evidence for an autocrine signaling system at term

Little is known about the mechanisms controlling the expression of key proteins that regulate excitability and contractility in the human myometrium at term. However, evidence is accumulating to suggest that the cytokine transforming growth factor (TGF)beta may play a central role. TGFbeta1 and TGFbeta receptors are present in the myometrial cells, indicative of an autocrine signaling system. Furthermore, the levels of TGFbeta1 and the expression of its receptors increase in the myometrium at term suggesting that they are, in turn, regulated and form part of a physiological cascade of events involving a number of autocrine signaling associated proteins. The present experiments were done to identify factors that regulate the expression of TGFbeta1 and TGFbeta receptors and may form other elements of this cascade. Because IL-1 and IL-8 are found in the myometrium at term and have been implicated in the etiology in premature labor we focus on this cytokines. Receptors for IL-1 and IL-8 were detected in the myometrial cells. Using Western blot analysis, the levels of expression were found to vary. The expression of IL-1 receptor type I was highest in the nonpregnant tissue with lower levels in nonlaboring myometrium with a further reduction in the spontaneously laboring tissue. In contrast, the expression of IL-8 receptor type B was highest in the pregnant nonlaboring tissue with a lower level in the spontaneously laboring tissue. Using an in vitro model, TGFbeta1 and TGFbeta receptor expression was up-regulated by IL-8, IL-1, and TGFbeta1 itself. However, IL-8 receptor expression was decreased by IL-8 and TGFbeta1. This suggests that in a cascade IL-8 would feed forward to promote the TGFbeta system, whereas TGFbeta1 feeds back to inhibit responsiveness to IL-8. Estrogen and progesterone increased the release of TGFbeta1. However, at high concentrations, estrogen and progesterone (100 nM 17beta-estradiol or 200 nM progesterone) decreased the level of TGFbeta receptor expression. Thus, the progressive rise of steroid levels in vivo might account for the observed changes in TGFbeta1 and TGFbeta receptor expression in vivo. Taken together, these observations support the idea that there is a cascade of autocrine signals that may play a major role in the physiological processes preparing the myometrium for parturition at term.

A phage-displayed mimotope inhibits tumour necrosis factor-alpha-induced cytotoxicity more effectively than the free mimotope

A phage-displayed peptide library was screened by direct interaction with human tumour necrosis factor-alpha (TNF-alpha) to identify novel antagonistic molecules of its biological activities. After several rounds of affinity selection, a phage displaying a mimotope sequence was shown to strongly inhibit, in a dose-dependent fashion, both mouse and human TNF-alpha-mediated cytotoxicity in L929 cells. The identified mimotope did not bear any sequence homology to the primary structures of the extracellular domains of either the 55 000 MW or the 75 000 MW TNF-alpha receptors, suggesting that it represents or mimics a conformational epitope involved with binding to TNF-alpha. The free 15-mer mimotope weakly inhibited TNF-alpha-induced cytotoxicity in vitro, and it did not bind to TNF-alpha as assessed by surface plasmon resonance, demonstrating the importance of mimotope presentation for its biological activities. In conclusion, this study highlights the potential of random combinatorial peptide libraries for the identification of novel inhibitors, which may serve as important tools in research that could lead to the development of TNF-alpha antagonists with therapeutic potential.

A Peptidomimetic Antagonist of TNF-α-Mediated Cytotoxicity Identified from a Phage-Displayed Random Peptide Library

Phage-displayed peptide libraries represent a vast collection of peptide sequences that can be used to identify novel therapeutic molecules. In this report, a 15-mer phage-displayed peptide library was used to identify potential TNF-α antagonists. After direct interaction of recombinant human TNF-α with the library, four randomly selected phage clones were shown to inhibit in a dose-dependent fashion both mouse and human TNF-α-induced cytotoxicity in vitro. DNA sequencing of the positive clones revealed a common amino acid sequence that does not bear any structural similarity to the known primary structures of the extracellular domains of either 55-kDa or 75-kDa TNF receptors. This sequence was synthesized, and the peptidomimotope was shown i) to bind to the recombinant human TNF-α using surface plasmon resonance (biosensor) technology and ii) to inhibit both recombinant mouse and human TNF-α-induced cytotoxicity in vitro in a dose-dependent fashion.

These findings highlight the potential of phage-displayed random peptide libraries for the identification of novel low molecular antagonistic molecules that can block the biologic activities of TNF-α.

Cytokine inhibitors in patients with heart failure and impaired functional capacity

Cytokines are proteins with pleiotropic biological effects, but the pathophysiologic role of cytokine inhibitors in advanced cardiac disease remains unclear. We assessed the levels of tumor necrosis factor (TNF)-alpha and its soluble receptors I (sTNF-RI) and II (sTNF-RII), soluble interleukin-1 receptor antagonist (sIL-1 Ra), and interleukin-6 soluble receptor (IL-6 sR) in sera from 11 patients with severe chronic congestive heart failure (mean left ventricular ejection fraction 19 +/- 6%; mean symptom-limited oxygen consumption 13 +/- 4 ml/min per kg) and 11 healthy volunteers. The serum concentrations of TNF, sTNF-RI, and sIL-1 Ra, but not of sTNF-RII and IL-6 sR, were significantly increased in heart failure patients. Importantly, their symptom-limited oxygen consumption was strongly associated with both sTNF-RI (R = -0.68, p = 0.04) and sIL-1 Ra (R = -0.77, p = 0.01). These results suggest that cytokine inhibitors from different receptor families may be involved in functional disability, a characteristic feature in patients with severe congestive heart failure. Understanding the response of cytokine inhibitors to heart failure might have therapeutic value as interventions against cytokines become available.

Interleukin-1beta-induced inhibition of hair growth in vitro is mediated by cyclic AMP

Interleukin (IL)-1 has been shown to be a potent inhibitor of hair growth in vitro. We hypothesized that this cytokine might be a decisive factor causing hair loss during the lymphocytic attack in alopecia areata. Neither the intracellular pathways involved in hair growth inhibition mediated by IL-1beta nor the signal transduction processes within hair follicles in general are known. We therefore investigated the intracellular signals involved in human hair growth in vitro. Hair follicles were isolated from scalp biopsies by microdissection, and hair growth was measured daily by image analysis. We assessed intracellular signal transducing elements using specific inhibitors or activators either alone or in combination with IL-1beta. The calcium ionophore A 23187 induced a rapid and complete arrest of hair growth, and phorbol-12-myristate-13-acetate (PMA), genistein, or IL-1beta decreased hair growth by approximately 60%-80%. IL-1beta-elicited hair growth arrest was not antagonized by calphostin C, a specific inhibitor of protein kinase C. In contrast, coincubation of IL-1beta with pertussis toxin or H 1004 neutralized the effect of IL-1beta, and dibutyryl-cAMP and cholera toxin, an activator of adenylate cyclase, inhibited hair growth. These data suggest that cAMP acts as a second messenger for IL-1beta-induced inhibition of hair growth. Moreover, our data indicate that in vitro hair growth is dependent on intracellular Ca2+ levels and activation of tyrosine kinase as well as protein kinase C. We were unable to detect a signal transducing element responsible for enhanced hair growth in vitro.

Time-course changes in serum cytokine levels in two experimental acute pancreatitis models in rats

Activated leukocytes and cytokines have important roles in the multi-system involvement during acute pancreatitis. The changes in the serum level of tumor necrosis factor-a (TNF-alpha) and interleukin-6 (IL-6) over time were investigated in two experimental acute pancreatitis models in rats. Mild edematous pancreatitis was induced with an overdose of cholecystokinin octapeptide (CCK-8), while a severe hemorrhagic form of pancreatitis was induced by ligation of the common bilio-pancreatic duct. The rats were examined 2, 4, 8, 16, 24 and 48 h after pancreatitis induction. The severity of the inflammation was assessed by measurement of the serum amylase activity, quantification of the edema, and histological examination. Serum TNF-alpha and IL-6 were determined by bioassay, using the TNF-sensitive WEHI 164 and the IL-6-dependent B9 cell lines, respectively. In CCK-8-induced acute pancreatitis, the pancreatic weight/body weight ratio (pw/bw) and amylase level were significantly elevated at 2 h, and the maximum levels were observed at 4 h (8.19 +/- 1.13 mg/g and 69.4 +/- 12.8 x 10(3) U/ml, respectively). Both parameters subsequently decreased continuously during the observation period. The serum IL-6 level was significantly increased at 4 h relative to the controls (123.3 +/- 5.8 vs 37.5 +/- 15 pg/ml), and then decreased continuously. In this model, only a moderate level of serum TNF-alpha was observed at 2 h. In the biliary type of acute pancreatitis, the ratio pw/bw increased continuously during the study and reached the maximum level at 48 h relative to the sham-operated control (8.8 +/- 1.4 vs 5.3 +/- 0.8 mg/g). The serum amylase level was significantly elevated at 2 h (43.2 +/- 13 x 10(3) U/ml), but then decreased continuously. The serum IL-6 reached its maximum level at 16 h (3800 +/- 447 pg/ml). In this model, increased TNF-alpha levels (75-300 U/ml) were measured 8, 16 and 24 h after pancreatitis induction. The results led to correlations between the serum IL-6 levels and the biochemical and morphological severity of acute pancreatitis in both experimental models. The data suggest that IL-6 and TNF-alpha may participate in the pathogenesis of these types of acute pancreatitis.

Cytokines: sources, receptors and signalling

Cytokines are a family of protein mediators that are important in transducing information between various cell types. These messengers are synthesized by a broad spectrum of cells. Cellular sources of cytokines include those cell types considered to play pivotal roles in the immune system as well as in inflammatory responses, including lymphocytes, monocytes and mast cells. Emerging data indicate that non-immune cells, including epithelial cells and fibroblasts, may also be important sources of certain cytokines. Cytokines fulfill a number of roles during immune and inflammatory reactions, and may display overlapping or redundant functions. In part, this redundancy may arise from the fact that cytokine receptors are not all unique entities, but may be divided into families. Many cytokine receptors have a subunit structure, with common subunits shared between receptors, and serving as affinity modifiers/signal transducers. Cytokines exert their effects on target cells by activating intracellular signalling mechanisms. In addition to 'classical' signal transduction path-ways, new data indicate that cytokines may also exemplify molecules that utilize novel signalling mechanisms, including the Jak-STAT pathways of transcriptional regulation and pathways involving the novel lipid second messenger, ceramide. In conclusion, molecular techniques have enabled the identification of many new cytokines, and the elucidation of their binding sites and mechanisms of action. This information has provided new insights into this complex area. Moreover, an understanding of the molecular basis of cytokine action and the pathways that lead to their acute and chronic effects may, in turn, facilitate interventions to prevent or modify their actions in disease states.

Recombinant human interleukin-1 receptor type I in the treatment of patients with active rheumatoid arthritis

OBJECTIVE

To determine the safety and efficacy of recombinant soluble human interleukin-1 receptor type I (rHuIL-1RI) administered subcutaneously in patients with active rheumatoid arthritis (RA).

METHODS

Twenty-three patients with active RA (>5 swollen joints) were enrolled into a randomized, double-blind, 2-center study. Patients received subcutaneous doses of rHuIL-1RI or placebo for 28 consecutive days. Patients were treated with 125, 250, 500, or 1,000 micrograms/m2/day of rHuIL-1RI. Physical examinations and laboratory assessments were performed at baseline (day 1), and 8, 15, 22, 29, 43, and 57 days after the start of the study. Analysis of peripheral blood by flow cytometry was performed on days 1 and 29 to determine the effects of rHuIL-1RI on the distribution and phenotypic characteristics of circulating inflammatory cells.

RESULTS

Four of 8 patients who received rHuIL-1RI at 1,000 micrograms/m2/day demonstrated improvement in at least 1 of 8 individual measures of disease activity; however, only 1 of these 4 patients experienced clinically relevant improvement as defined by predetermined criteria. None of the patients treated with smaller doses of rHuIL-1RI, and none of the placebo-treated control patients, experienced any improvement as defined by the predetermined criteria. Monocyte cell surface IL-1alpha was significantly reduced following treatment with rHuIL-1RI at each dosage. Administration of rHuIL-1RI was stopped prematurely because of dose-limiting rashes in 2 patients treated with 1,000 micrograms/m2/day. No other adverse events prevented completion of the study.

CONCLUSION

Only 1 patient, who was treated with the highest concentration of rHuIL-1RI employed (1,000 micrograms/m2/day), demonstrated clinically relevant improvement in this phase I study on this small group of patients with active RA. Dose-limiting toxicity was also observed in 2 patients treated with this highest concentration of rHuIL-1RI. Treatment with rHuIL-1RI did result in a reduction of monocyte cell surface IL-1alpha, which indicates that the dosages of rHuIL-1RI employed were functional.

Lymphocyte activation and cytokine production in autoimmune hemolytic anaemia (AIHA)

We studied 16 patients affected by autoimmune hemolytic anaemia (AIHA), both idiopathic and associated with other diseases (B and T lymphoma, B hepatitis, gastric carcinoma, systemic lupus erythematosus) or alpha-methyldopa therapy, in order to value T- and B-cell activation. We determined the count of T- and B-cell subsets in peripheral blood, the proliferative response of peripheral blood lymphocytes (PBL) to phytohemagglutinin (PHA) and to pokeweed mitogen (PWM), the percentage of CD25+ cells in culture and interleukin (IL)-1alpha, IL-2, IL-4, tumor necrosis factor (TNF)alpha and soluble IL-2 receptor (sIL-2R) levels in sera and in culture. Except for an increase in CD4+ and CD8+ T cell number in a case of AIHA associated with a T lymphoma and an increase in the percentage of CD5+ and PCA1+ B cells in two cases of AIHA associated with B lymphoma and with SLE, no further data showed a relationship with the disease possibly associated with AIHA, so both idiopathic and secondary AIHA cases were analyzed together. CD4+ T cells were reduced in number in 9 cases, while CD8+ T cells were reduced in 6 cases. The percentage of CD5+ B cells was increased in 5 cases. The percentage of PCA1+ cells was increased in all cases (mean +/- sd: 18 +/- 22 vs 0,2 +/- 1 in controls). The average PBL proliferative response to PHA was reduced (S.I. 71 +/- 55 vs 138 +/- 45 in controls) as well as that to PWM (S.I. 27 +/- 21 vs 75 +/- 24 in controls), despite IL-2 high levels, in all cases, in both sera (mean +/- sd: 648 +/- 351 pg/ml vs 16 +/- 4 pg/ml in controls) and culture supernatants (mean +/- sd: 1045 +/- 677 pg/ml vs 195 +/- 51 pg/ml in controls). In PHA stimulated cultures the percentage of CD25+ cells was reduced (mean +/- sd: 37 +/- 18 vs 63 +/- 14 in controls), sIL-2R levels were like controls in 7 cases. In sera sIL-2R levels were increased in all cases (mean +/- sd: 1256 +/- 465 U/ml vs 256 +/- 114 U/ml in controls), IL-1alpha was increased in all cases too, while IL-4 levels were increased only in 7 cases. Linear regression analysis generally showed a low relationship between S.I. and IL-2, IL-4 and sIL-2R levels in supernatants of PHA stimulated culture as well as between S.I. and the percentage of CD25+ cells. Taken together these data suggest a state of B- and T-cell hyperactivation in AIHA. The low PBL proliferative response in vitro, explained in previous studies as a temporary functional exhaustion, might be itself a sign of the complete lymphocyte activation occurring in vivo in AIHA.

Neuropsychiatric aspects of cytokines research: an overview

Cytokines are a group of proteins primarily synthesized by various immune cells. They have multiple functions within the immune system and have been implicated in a number of disease states. There is growing evidence that some cytokines are also synthesized in the central nervous system. Taking into consideration that some cytokines are also capable of inducing behavioral effects, it has been suggested that cytokines may play a role in some psychiatric and neurologic disorders.

Mitogenic effects of interleukin-5 on microglia

Interleukin-3 (IL-3), interleukin-5 (IL-5), and granulocyte macrophage-colony stimulating factor (GM-CSF) are cytokines that bind to receptor complexes comprised of unique alpha-receptor subunits specific for each ligand and a commonly shared beta-receptor subunit. Previous studies have shown that IL-3 and GM-CSF induce mitosis in microglia and macrophage cells, indicating the functional presence of their cognate receptors. In this study, it is shown that the third member of this cytokine group, IL-5, also serves as a microglia mitogen. Proliferative effects were seen in culture on both murine microglia and a murine macrophage cell line, RAW 264.7. Since IL-5 is known to be secreted by both microglia and astrocytes in response to inflammatory stimuli, these results indicate that IL-5 may be involved in the cytokine-immune cascades leading to microglia proliferation in areas affected by disease and tissue damage.

Tumor necrosis factor-alpha and the failing human heart

Tumor necrosis factor-alpha (TNF alpha) is a proinflammatory cytokine with negative inotropic effects. Recently, elevated levels of TNF alpha have been identified in patients with advanced heart failure. Although the clinical significance of this finding is unclear at present, there is increasing evidence that this cytokine may play a primary pathophysiologic role in the development and pathogenesis of heart failure in humans. Indeed, many of the clinical hallmarks of heart failure, including left ventricular dysfunction, cardiomyopathy, and pulmonary edema can be explained by the known biological effects of TNF alpha in humans. The present review will summarize recent evidence with regard to the biological role for TNF alpha in the adult mammalian heart, as well as summarize the increasing body of clinical information that implicates this cytokine in the pathophysiology of heart failure.

Functional consequences of APO-1/Fas (CD95) antigen expression by normal and neoplastic hematopoietic cells

Murine monoclonal antibody (mAb) 7C11 binds to the same cell surface epitope as anti-APO-1 and anti-Fas and reacts specifically with cells transfected with a cDNA encoding the human Fas antigen. Furthermore, incubation with 7C11 causes death of hematopoietic cell lines that express APO-1/Fas but not APO-1/Fas-negative cell lines. 7C11 therefore recognizes the human APO-1/Fas (CD95) antigen, a 40 to 50 kDa cell surface glycoprotein that can trigger apoptosis or programmed cell death. Expression of APO-1/Fas antigen by normal and neoplastic hematopoietic cells was determined by flow cytometry using 7C11. APO-1/Fas is expressed by approximately 30 to 40% of resting peripheral blood T cells, B cells, and monocytes and by approximately 5% of resting NK cells and thymocytes. It was not detected on granulocytes, erythrocytes, or platelets. Approximately 80 to 90% of activated T cells, B cells, and thymocytes express APO-1/Fas, as do the majority of activated NK cells. Perturbation of APO-1/Fas by 7C11 does not affect the viability of resting lymphocytes or monocytes. In contrast, activated T cells and NK cells undergo apoptosis within 3 hours of exposure to 7C11. Other mAb that stimulate T cells or NK cells do not cause rapid induction of programmed cell death. APO-1/Fas antigen is expressed by many cell lines of lymphoid and myeloid lineage. However, this antigen was detected on neoplastic cells from only one of 69 patients with acute myeloid leukemia, acute lymphoblastic leukemia, chronic myelogenous leukemia, chronic lymphocytic leukemia, or multiple myeloma. Only 3 out of 25 tumor samples from patients with non-Hodgkin's lymphoma were found to express APO-1/Fas. All three of these lymphomas harbored the bcl-2-Ig fusion gene associated with the chromosomal translocation t (14;18). Conversely, only 27% of lymphomas that possessed the bcl-2-Ig gene were found to express the APO-1/Fas antigen. Like normal activated lymphocytes, leukemia and lymphoma cells that expressed APO-1/Fas antigen were found to undergo apoptosis in vitro after incubation with 7C11. The APO-1/Fas antigen appears to regulate the growth of normal hematopoietic cells, and the marked upregulation of this antigen on activated normal lymphocytes contrasts sharply with the absence of APO-1/Fas on neoplastic cells of hematopoietic lineage. Defects in the apoptotic signal delivered through this antigen might contribute to the pathogenesis of hematopoietic neoplasms. Thus, the gene encoding APO-1/Fas can be considered a novel type of tumor suppressor gene, just as bcl-2 can be considered a cellular proto-oncogene.

Soluble interleukin-6 receptors in inflammatory bowel disease: relation to circulating interleukin-6

The in vivo appearance of soluble interleukin (IL)-6 receptor (sIL-6R) in serum from patients with inflammatory bowel disease was examined using an enzyme linked immunosorbent assay (ELISA). The serum sIL-6R concentrations in patients with active disease (ulcerative colitis, 148.4 (5.1); Crohn's disease, 142.3 (9.3) ng/ml; mean (SEM)) were significantly raised compared with those in patients with inactive disease (ulcerative colitis, 116.2 (7.2); Crohn's disease, 114.3 (7.1) ng/ml), some other type of colitis (104.8 (11.6) ng/ml), or in normal subjects (107.3 (2.4) ng/ml). These differences were also seen in paired samples examined during both active and inactive phases. Additionally, serum sIL-6R and IL-6 concentrations correlated significantly with C-reactive protein levels in both ulcerative colitis and Crohn's disease patients (r = 0.23 and 0.56, respectively; p < 0.05 for both). Furthermore, gel filtration analysis of serum from these patients showed two major peaks of immunoreactive IL-6-one peak corresponding to free IL-6 and another peak to sIL-6R-bound IL-6-this was further confirmed by a luminescence sandwich ELISA. These results, together with its in vitro effects, indicate that natural sIL-6R may function as a powerful enhancer of the IL-6-dependent immune processes observed in inflammatory bowel disease.

The type II 'decoy' receptor: a novel regulatory pathway for interleukin 1

The interleukin 1 (IL-1) system plays a central role in inflammation and immunity. Of the two receptors that bind IL-1, the type I receptor is known to mediate signaling activity, whereas the function of the type II receptor remains unknown. Here, Francesco Colotta and colleagues review the properties of these receptors and summarize evidence indicating that the type II receptor acts as a regulated decoy target for IL-1.

The human OX40 homolog: cDNA structure, expression and chromosomal assignment of the ACT35 antigen

Tissue distribution and expression on mitogen and virally stimulated lymphocytes render the ACT35 molecule a human lymphocyte activation antigen which as yet could not be clustered. Expression cloning of the ACT35 antigen from a pCDM8 library of the HUT-102 cell line revealed strong homology of the cDNA and its encoded protein sequence with the formerly described rat OX40 antigen. The 1.4-kb nucleotide sequence and the deduced 277-amino acid sequence of the single transmembrane protein were 65% and 63% identical, in human and in rat, respectively. Conservation included one N-linked glycosylation site and one protein kinase C phosphorylation site. When expressed in COS-1 cells, the cDNA presented properties comparable to the native ACT35 antigen and the rat OX40 molecule (relative molecular mass 48,000). Thus, the ACT35 protein corresponds to the hitherto unknown human OX40 antigen and is, therefore, another member of the tumor necrosis factor/nerve growth factor receptor (TNFR/NGFR) family. After applying fluorescence in situ hybridization, the human ACT35/OX40 gene could be mapped to chromosome band 1p36 and is, thus, linked to the genes for TNFR II and CD30.

Cytokine receptors and signal transduction

Cytokines are important regulators of hemopoiesis which exert their actions by binding to specific, high affinity, cell surface receptors. In the past several years, molecular cloning of these receptors has revealed a new superfamily referred to as the hemopoietic growth factor receptors. Members of this family are defined by a 200 amino acid conserved domain; however, it has become increasingly apparent that another characteristic of these receptors is the shared usage of a common signalling subunit among subgroups in this family. The shared signalling component explains the functional redundancy of many cytokines; however, the mechanism by which these receptors transduce a signal across the membrane is not yet clear. Studies into cytokine action have shown that many of the events that occur in response to ligand stimulation are similar to those observed for the better characterized intrinsic tyrosine kinase receptors. Thus, although the cytokine receptors do not possess intrinsic tyrosine kinase activity, these observations have led to a model of cytokine signal transduction adapted from the signalling mechanisms described for the tyrosine kinase receptors.

Cytokine involvement in viral permissiveness and the progression of HIV disease

Many viruses have evolved novel means of exploiting host defense mechanisms for their own survival. This exploitation may be best exemplified by the interrelationships between certain viruses and the host cytokine networks. Many viruses, including the human immunodeficiency virus type-1 (HIV-1), rely on the liberation and cellular action of host immune cytokines to expand their host cell range, to regulate their cellular expression, and to maintain their dormant state until the proper extracellular conditions arise. As again exemplified by HIV-1, viruses may also take an active role regulating cytokine expression and cell surface cytokine receptors. Because the viral life cycle, and in particular the HIV-1 life cycle, is so intertwined with cytokine regulatory networks, these networks represent potential points for therapeutic intervention. As our understanding of cellular cytokine pathways involved in viral infection and replication continues to expand, so too will our ability to design rational anti-viral therapies to alter multiple steps along the viral life cycle.