Understanding the link between the IL-6 cytokine family and pregnancy: implications for future therapeutics

Cytokines are involved in almost all processes during the menstrual cycle, the fertilization period and pregnancy. They are expressed in numerous reproduction-related body fluids and tissues. Disorders of cytokine expression patterns may cause pregnancy pathologies. Therefore, cytokines have the potential as new biomarkers in different body compartments for a variety of such pathologies. Furthermore, cytokines may also serve to treat fertility and pregnancy disorders. The IL-6-like family of cytokines is an intensively investigated group of cytokines with well-accepted functions in fertility and pregnancy. This article summarizes current knowledge on IL-6-like cytokines in regard of their role in reproduction and their potential for new strategies in the treatment of reproductive pathologies.     

IL-6 cytokine family and signal transduction: a model of the cytokine system

The interleukin 6 (IL-6) cytokine family, which includes IL-6, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), IL-11 and cardiotrophin-1 (CT-1), exhibits pleiotropy and redundancy in biological activities. The IL-6 family cytokines exhibit a helical structure. Their receptors belong to the type 1 cytokine receptor family. The receptors of the IL-6 family cytokines share a receptor subunit, which explains one of the mechanisms of functional redundancy. In this review, we describe the general features of the IL-6 cytokine family and its signal transduction mechanisms. Many functional properties of the IL-6 family of cytokines and their receptors are general features of the cytokine system.     

Recent advances in the IL-17 cytokine family

The IL-17/IL-17 receptor family is the newest and least understood of the cytokine subclasses. Composed of ligands IL-17A-IL-17F and receptors IL-17RA-IL-17RE, these cytokines have many unique structural and functional features. Since the discovery of the 'Th17' subset in 2005, particular attention has been paid to IL-17A and IL-17F and their cognate receptors. To date, far less is known about the rest of the family. This review discusses recent advances in the field, with an emphasis on IL-17A biology.     

Interleukin-33 (IL-33): A nuclear cytokine from the IL-1 family

Interleukin-33 (IL-33) is a tissue-derived nuclear cytokine from the IL-1 family abundantly expressed in endothelial cells, epithelial cells and fibroblast-like cells, both during homeostasis and inflammation. It functions as an alarm signal (alarmin) released upon cell injury or tissue damage to alert immune cells expressing the ST2 receptor (IL-1RL1). The major targets of IL-33 in vivo are tissue-resident immune cells such as mast cells, group 2 innate lymphoid cells (ILC2s) and regulatory T cells (Tregs). Other cellular targets include T helper 2 (Th2) cells, eosinophils, basophils, dendritic cells, Th1 cells, CD8⁺ T cells, NK cells, iNKT cells, B cells, neutrophils and macrophages. IL-33 is thus emerging as a crucial immune modulator with pleiotropic activities in type-2, type-1 and regulatory immune responses, and important roles in allergic, fibrotic, infectious, and chronic inflammatory diseases. The critical function of IL-33/ST2 signaling in allergic inflammation is illustrated by the fact that IL33 and IL1RL1 are among the most highly replicated susceptibility loci for asthma. In this review, we highlight 15 years of discoveries on IL-33 protein, including its molecular characteristics, nuclear localization, bioactive forms, cellular sources, mechanisms of release and regulation by proteases. Importantly, we emphasize data that have been validated using IL-33-deficient cells.     

Interleukine-6 (IL-6) may be a link between myasthenia gravis and myoepithelioma of the parotid gland

Myoepithelioma is a rare benign neoplasm of the salivary glands occurring more frequently in the parotids. Myasthenia gravis (MG) is a chronic, T-cell dependent, antibody and complement-mediated autoimmune neuromuscular transmission disorder. Interleukine-6 (IL-6) is an immune protein belonging to the family of the hematopoietins, liberated in response to infection, burns, trauma, and neoplastic diseases. It seems that an overproduction of IL-6 might play an important role in the pathophysiology of MG. Moreover, it has been discussed the possible role of IL-6 as a modulating factor either in proliferation or in differentiation of pleomorphic adenoma cell line into myoepithelioma. The authors present a rare case of parotid myoepithelioma occurred in a patient affected by myasthenia gravis and suppose a possible IL-6 mediated relationship between myasthenia gravis and parotid myoepithelioma.     

Filaggrin mutations and atopy: consequences for future therapeutics

Filaggrin is a key component of the epidermal differentiation complex of the stratum corneum in the epidermal layer of human skin. Loss-of-function mutations in filaggrin have been described in patients with atopic eczema and are associated with an increased risk of atopic sensitization in these individuals. Atopic eczema is the first stage of the atopic march that describes the phenomenon of increased rates of allergic rhinitis and allergic asthma observed in individuals with early atopic dermatitis. The skin barrier disruptions of atopic eczema associated with loss-of-function mutations in filaggrin are thought to provide a nidus for allergic sensitization to food and aeroallergens, which can then lead to increased allergic disease. It is on this foundation that therapies aimed at restoration of barrier function are thought to play a role, not only in the effective treatment of atopic eczema, but also in the prevention of further allergic disease development.     

Molecular interactions within the IL-6/IL-12 cytokine/receptor superfamily

Production of cytokines by immune cells in response to stimuli and the binding of cytokines to specific receptors on target cells is a central feature of the immune response. The IL-12 cytokine family is particularly influential in determining the fate of T cells and is characterized by the sharing of cytokine and receptor subunits. A thorough understanding of the molecular interactions within this family will be a key to the development of therapeutic inhibitors or enhancers of IL-12 family function. While the current structural and molecular data for IL-12 family members is limited, there is ample information on the structurally related IL-6 cytokine family. This review will summarize the current structural and mutagenesis data within the IL-12 family and will attempt to utilize similarities between the IL-6 and IL-12 families to understand molecular interactions between IL-12 family subunits and with receptor components.     

Distinct subunit pairing criteria within the heterodimeric IL-12 cytokine family

The heterodimeric IL-12 cytokine family is characterized by the sharing of three α (p19, p28, p35) and two β (p40 and Ebi3) subunits, and includes IL-12 (p35/p40), IL-23 (p19/p40), IL-27 (p28/Ebi3) and IL-35 (p35/Ebi3). In this study, the dimerization interfaces of IL-12 family members were characterized, with emphasis on IL-35. Ebi3 and p35 subunits from human and mouse paired effectively with each other, indicating there is no species barrier to IL-35 dimerization and suggesting a conserved dimerization interface. Specific p35 residues that contribute to formation of the IL-12 interface were assessed for their contribution to the IL-35 interface, and candidate Ebi3 residues were screened for their contribution to both IL-27 and IL-35 interfaces. Several residues were identified as critical to the IL-12 or IL-27 interfaces. Conversely, no single mutation was identified that completely disrupts p35/Ebi3 pairing. Linear alanine scanning mutagenesis on both p35 and Ebi3 subunits was performed, focusing on residues that are conserved between the mouse and human proteins. Additionally, a structure-based alanine-scanning approach in which mutations were clustered based on proximitiy was performed on the p35 subunit. Both approaches suggest that IL-35 has distinct criteria for subunit pairing and is remarkabley less sensitive to structural perturbation than IL-12 and IL-27. Additionally, studies using a panel of anti-p35 and anti-Ebi3 antibodies indicate differential availability of epitopes within IL-12 family members that share these subunits, suggesting that IL-35 has distinct structural features, relative to IL-12 and IL-27. These results may be useful in future directed therapeutic targeting of IL-12 family members.     

The IL-17 cytokine family and their role in allergic inflammation

Allergic diseases and asthma has long been hypothesized as the results of the dysregulation of type 2 immune responses to environmental allergens. Recent progresses in characterizing the proinflammatory IL-17 cytokine family have added additional layer of complexity on the regulation of allergic inflammation. The delineation of IL-17-producing CD4+ T cell subset (Th17) has led to the revision of Th1/Th2 paradigm and impacts our perspectives on the basis of chronic tissue inflammation. In addition, the distinctive expression patterns and biological activities of individual IL-17 cytokine member may play different roles in the regulation of the pathogenesis of allergic diseases. Understanding the cellular source and targeting cells of IL-17 cytokine family member will provide the basis to elucidate the cellular mechanism underlying allergic inflammation and improve our therapeutic approaches for allergy.     

Lack of association between pro-inflammatory cytokine (IL-6, IL-8 and TNF-alpha) gene polymorphisms and Graves' disease

Graves' disease (GD) is a common, autoimmune disease involving the thyroid gland, and it has been previously suggested that pro-inflammatory cytokines are involved in the disease's pathogenesis. The aim of this study was to test whether the interleukin (IL)-6 gene promoter region, or tumour necrosis factor (TNF)-alpha or IL-8 gene 3'-untranslated region (3'-UTR) polymorphisms could provide useful genetic markers for an individual's susceptibility to GD. A normal control group of 60 healthy people and 95 patients featuring GD were examined. Polymerase chain reaction (PCR)-based restriction analysis was performed for the three gene polymorphisms using endonucleases BsrBI, NcoI and ApaLI, respectively. We found no significant difference between the frequencies of genotype and allelic variants for the IL-6 gene promoter (-572 G/C), the TNF-alpha gene promoter (-308 A/G) and the IL-8 gene 3'-UTR (2767 A/G) for GD patients and for normal controls. Cytokines are a large group of proteins that may elicit multiple effects upon immunological reactions. It still appears to be very worthwhile to continue to aggressively search for cytokine gene polymorphisms in order to predict the development of such disease.     

Activation of eosinophils by IL-12 family cytokine IL-27: Implications of the pleiotropic roles of IL-27 in allergic responses

Interleukin (IL)-27 is a novel IL-12 family cytokine and its immunomodulatory effects on T-lymphocytes, B-lymphocytes and mast cells were extensively studied. IL-27 could suppress Th2-mediated allergic diseases in mouse models. However, the role of IL-27 on eosinophils, the principal effector cells in allergic diseases, remains unexplored. Our present study revealed that eosinophils constitutively express functional IL-27 receptor heterodimer, gp130 and WSX-1. IL-27 could prolong eosinophil survival by reducing apoptosis, modulate the expression of adhesion molecules to facilitate eosinophil adhesion and accumulation, and induce the release of proinflammatory cytokines IL-6, tumor necrosis factor-α, IL-1β and chemokines CCL2, CXCL8 and CXCL1. The stimulation effects of IL-27 on eosinophils could not be abrogated by Th2 cytokine IL-25, hematopoietic cytokine granulocyte macrophage colony-stimulating factor, and toll-like receptor 4 ligand lipopolysaccharide (LPS). These findings are different from the effects of IL-27 and LPS on monocytes. Intracellular signaling mechanistic studies showed that IL-27-mediated eosinophil activation was differentially regulated by the activation of extracellular signal-regulated kinase, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase, as well as nuclear factor-κB. Based on the above results, IL-27 could play crucial roles in allergic diseases by the activation of eosinophils via differential intracellular signaling cascades. According to the present findings of its activating effects on human eosinophils, IL-27 may play pleiotropic roles in human allergic responses.     

细胞因子IL6、IL8及IL-10与变应性鼻炎的关系研究

目的探讨白细胞介素-6、8、10与变应性鼻炎（allergicrhinitis,AR）发病的相关性,为指导临床治疗提供实验依据。方法应用酶联免疫吸附测定（enzymelinkedimmu—nosorbentassay,ELISA）方法检测35例正常健康对照组以及60例变应性鼻炎患者脱敏治疗前后血清标本中IL-6、IL-8、IL-10的表达水平,并应用SPSSl3．0软件分析治疗前后各指标的表达差异,以及三者之间的相关性。结果IL-6、IL-8在AR患者血清中高表达,与健康对照组相比差异具有显著性（t=15．213,P〈0．01;t=12．231,P〈0．01）,脱敏治疗后表达均下降,治疗前后差异具有统计学意义（t=21．995,P〈0．01;t=19．766,P〈0．01）;IL-10在患者血清中表达低于对照组（t=7．446,P〈0．01）,脱敏治疗后其表达上升,与治疗前相比差异显著（t=10．228,P〈0．01）;IL-6、IL-8在AR患者中的表达呈正相关（r=0．523。P〈0．01）,而二者与IL-10的表达呈负相关（r=-0．482,P〈0．01）。结论IL-6、IL-8及IL-10与变应性鼻炎发病过程密切相关,相应的细胞因子或拮抗剂将可能成为候选的治疗药物。     

CTLA-4 and IL-6 gene polymorphisms: Risk factors for recurrent pregnancy loss

The purpose of the present study was to evaluate the possible association between CTLA-4 +49A/G and IL-6 −634C/G polymorphisms, and the risk of recurrent pregnancy loss (RPL). 240 women (120 healthy controls and 120 with RPL) were enrolled in this case-control study. Genotyping was performed using a PCR-RFLP technique. In the case of polymorphic CTLA-4 +49A/G, the wild type allele G was associated with a decreased risk of RPL (OR: 0.42, 95%CI: 0.25–0.69, p = 0.001). As to IL-6 −634C/G polymorphism, a highly significant difference was observed, and those women who carry at least one mutant G allele presented a probability of developing RPL about 5 times greater than controls (OR: 5.1, 95%CI: 1.04–25.3, p = 0.04). The results indicate that polymorphisms of CTLA-4 and IL-6 genes may influence the risk of developing RPL among Iranian women, suggesting that more research on the immunogenetics of pregnancy should be conducted to confirm our results, and to declare the exact roles of studied molecules in RPL pathogenesis.     

Developmental regulation of the cytokine repertoire in human macrophages: IL-1, IL-6, TNF-alpha, and M-CSF

We were interested in the dependence of constitutive and stimulated cytokine secretion on the stage of macrophage (MAC) differentiation in vitro. Elutriation-purified blood MO were cultured up to 28 days and their secretory repertoire was analyzed under adherence conditions at various culture stages. For each of the cytokines tested, interleukin (IL)-1 beta, IL-6, tumor necrosis factor (TNF)-alpha, and macrophage colony-stimulating factor (M-CSF), a different pattern of regulation was observed. During the initial phase of maturation (up to day 7 in culture) within which the characteristics of normal MO to MAC transformation are achieved, M-CSF was the only cytokine to be secreted constitutively. From the LPS-dependent cytokines, IL-1 beta and IL-6 were downregulated whereas TNF-alpha levels increased severalfold. For the release of IL-1 beta, IL-6, and TNF-alpha a synergistic effect of interferon-gamma (IFN-g) and lipopolysaccharide (LPS) was observed. M-CSF release increased until day 7 in culture with LPS being stimulatory for this particular cytokine only during the first days of differentiation. Upon further cultivation of MAC up to 28 days, LPS-induced IL-1 beta levels remained very low, but IL-6 levels increased again reaching that of blood MO, and TNF-alpha continued to rise reaching levels up to 30-fold higher than in blood MO. M-CSF secretion stayed high with LPS even suppressing constitutive secretion. Long-term cultured MAC started to release IL-6 and TNF-alpha also in the absence of a stimulus and, furthermore, became responsive to IFN-g alone. Our data show that the release of each cytokine investigated is differently regulated during maturation. These results document the functional plasticity of human MAC and emphasize the impact that MO to MAC differentiation may have in vivo.