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-like cytokines and cancer cachexia

An estimated 30% of cancer deaths are attributed to cachexia and its consequences. Cachexia (wasting syndrome) is the hypercatabolism of the body's carbon sources, proteins and lipids, for conversion into energy. It is induced by a variety of pathological conditions, including cancer. Among the inflammatory responses to cancer is the synthesis of cytokines, including IL-6 and related cytokines. These cytokines have been found to induce cach exia by altering metabolism of lipids and proteins. IL-6-like cytokines have been found to inhibit lipid biosynthesis by adipocytes, which increased the rate of lipid catabolism. Others have described the atrophy and increased catabolism of muscle protein due to IL-6. A cytokine closely-related to IL-6 is leptin, which plays a major role in lipid metabolism under normal conditions. The role of leptin in pathological conditions such as cancer cachexia has not yet been fully elucidated. Detailed mechanistic information about the induction of cancer cachexia by IL-6-like cytokines requires more research.     

Changes in urinary cytokines and soluble intercellular adhesion molecule-1 (ICAM-1) in bladder cancer patients after bacillus Calmette-Guérin (BCG) immunotherapy.

Intravesical immunotherapy for carcinoma in situ of the bladder is arguably the most effective form of tumour immunotherapy described to date. Following repeated instillations of BCG organisms into the bladder, large quantities of cytokines are detected in patients' urine. This study concerns the production of IL-1 beta, IL-2, IL-4, IL-6, IL-8, IL-10, tumour necrosis factor-alpha (TNF-alpha), interferon-gamma (IFN-gamma) and soluble ICAM-1 (sICAM-1) throughout the six weekly instillations which comprise a therapeutic course. Sequential instillations of BCG induced secretion of IL-1 beta, IL-2, IL-6, IL-8, IL-10, TNF-alpha, IFN-gamma and sICAM-1 into urine. The responses were heterogeneous between patients and cytokines, but some general trends were evident. Although cytokine levels were initially low, their concentration increased with repeated instillation of BCG. Certain cytokines (e.g. IL-6, IL-8 and IL-10) could be detected after the first instillation, whilst others (e.g. IL-2 and IFN-gamma) were not detected until after the third or fourth instillation. Interestingly, IL-4 was not detected, perhaps suggesting a differential effect on Th2-like responses. Some patients produced particularly elevated or non-detectable levels of cytokines, and a positive correlation was found between the production of various cytokines. The production of a particular cytokine did not correspond with lack of production of another species. Whether monitoring the production of cytokines following therapy may be of prognostic value will be determined in a larger series of patients. However, as these potent immunomodulators are thought to be important for the 75% complete clinical response observed with BCG therapy, there remains the possibility that detection of the products of an activated immune system may correlate with eventual clinical outcome. This study is a necessary forerunner to full prognostic evaluation of such immunological data.     

Involvement of serum and lipopolysaccharide in the production of interleukin-1- and interleukin-6-like molecules by human sperm cells

PROBLEM: To examine the capacity of sperm cells from fertile and infertile men to secrete interleukin (IL)-6, and the involvement of serum factors and lipopolysaccharide (LPS) in the regulation of IL-6 and IL-1 production by sperm cells. METHODS: Swim-up sperm cells from fertile (donors) and oligoteratoasthenospermic (OTA)-infertile men were incubated with or without 5% fetal calf serum (FCS) and LPS (10 microg/mL) for 2-24 hr. After incubation, IL-6 and IL-1 bioactivities were measured in supernatants and lysates by specific bioassays (B9 cell proliferation assay and 1A-5 system, respectively). RESULTS: IL-6- and IL-1-like activities were observed to be produced by swim-up sperm cells from both study groups. Stimulation of swim-up sperm cells with either LPS or FCS or both together did not affect their capacity to produce IL-1. However, LPS, but not serum increased the secretion levels of IL-6 by swim-up sperm cells. CONCLUSIONS: Swim-up sperm cells from both study groups constitutively produce IL-6 and IL-1, and serum components did not affect this capacity. However, LPS was shown to increase the capacity of swim-up sperm cells of both study groups to secrete IL-6, but not IL-1. Cytokines may be involved in the physiology and pathophysiology of sperm functions and, thus, may affect male fertility.     

Changes in cytokine production during and after normal pregnancy

PROBLEM: The systemic T helper 1/T helper 2 (Th1/Th2) cytokine balance during normal human pregnancy is controversial, and observations about the balance in the postpartum period have only been reported for up to 3 months. METHOD: Whole-blood, from 83 healthy pregnant women, 80 healthy postpartum women, and 31 healthy non-pregnant women was stimulated with phorbol 12-myristate 13-acetate (PMA) and ionomycin, and the levels of cytokines in the supernatant were measured by enzyme-linked immunosorbent assay (ELISA). RESULTS: The production of all measured cytokines decreased during pregnancy, especially in the second trimester. After delivery, interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) increased from 2 to 11 months postpartum, and IL-4 increased from 6 to 11 months postpartum. CONCLUSIONS: These data indicate that 1) decreases in production of both Th1-and Th2-type cytokines during pregnancy may be related to the pregnancy-induced amelioration of autoimmune diseases: 2) increases in production of both Th1- and Th2-type cytokines in the postpartum period may be related to the postpartum aggravation of autoimmune diseases.     

A type 2 (Th2-like) pattern of immune response predominates in the pulmonary interstitium of patients with cryptogenic fibrosing alveolitis (CFA).

CFA is an inflammatory condition of the lungs resulting in scarring, pulmonary failure and death. The etiology of the disease is unknown, but the pathogenesis is believed to involve a persistent immunological reaction to unidentified antigen in the lung resulting in tissue damage. Recent advances in our understanding of the immune system have shown that different patterns of stimulatory cytokines are produced at sites of inflammation by a range of cell types. Patterns of cytokine reproduction by inflammatory cells are recognized to be associated with different patterns of immunological response, and these have been described as type 1 (or Th1-like) and type 2 (or Th2-like) on this basis. We have studied cytokine expression in the intestinal inflammatory cell infiltrate in lung tissue from patients with CFA using mRNA in situ hybridization and immunohistochemistry. Our results show that while there is evidence for both a type 1 (characterized by interferon-gamma (IFN-gamma) and type 2 (characterized by IL-4 and IL-5) response present in CFA, the type 2 (or Th2) pattern of cytokines appears to predominate. This would be consistent with a possible role for the humoral immune response in the pathogenesis of this condition. In addition, recent evidence suggests that IL-4 and IFN-gamma may be important regulatory factors for pulmonary fibroblasts. The relative paucity of IFN-gamma may contribute to the excessive fibroblast activation, deposition of collagen and scar formation that occurs in CFA.     

The group 2 innate lymphoid cell (ILC2) regulatory network and its underlying mechanisms

Group 2 innate lymphoid cells (ILC2s) play critical roles in the induction of type 2 inflammation, response to parasite infection, metabolic homeostasis, and tissue repair. These multifunctional roles of ILC2s are tightly controlled by complex regulatory systems in the local microenvironment, the disruption of which may cause various health problems. This review summarizes up-to-date knowledge regarding positive and negative regulators for ILC2s based on their function and signaling pathways, including activating cytokines (IL-33, IL-25; MAPK, NF-κB pathways), co-stimulatory cytokines (IL-2, IL-7, IL-9, TSLP; STAT5, IL-4; STAT6, TNF superfamily; MAPK, NF-κB pathways), suppressive cytokines (type1 IFNs, IFN-γ, IL-27; STAT1, IL-10, TGF-β), transdifferentiation cytokines (IL-12; STAT4, IL-1β, IL-18), lipid mediators (LTC4, LTD4, LTE4, PGD2; Ca²⁺-NFAT pathways, PGE2, PGI2; AC/cAMP/PKA pathways, LXA4, LTB4), neuropeptides (NMU; Ca²⁺-NFAT, MAPK pathways, VIP, CGRP, catecholamine, acetylcholine), sex hormones (androgen, estrogen), nutrients (butyrate; HDAC inhibitors, vitamins), and cell-to-cell interactions (ICOSL-ICOS; STAT5, B7-H6-NKp30, E-cadherin-KLRG1). This comprehensive review affords a better understanding of the regulatory network system for ILC2s, providing impetus to develop new treatment strategies for ILC2-related health problems.     

Constitutive Secretion of Interleukin-6 by Human Decidual Stromal Cells in Culture. Regulatory Effect of Progesterone

PROBLEM : Although several studies have demonstrated that decidual stromal cells (DSC) can secrete cytokines in culture, none of these studies documented the purity of the cultures. Since other cells of the decidua, such as macrophages and epithelial cells, also produce cytokines, it is important to ensure purity of the culture so that cytokine production can be ascribed with confidence to DSC. METHOD : DSC from early human pregnancies were highly purified and maintained in culture. Basal secretion by these cells of IL-6, together with other cytokines considered critical for pregnancy (IL-1β, TNFα and IFNγ), was measured with immunological techniques. RESULTS : We found that DSC in culture produce insignificant quantities of IL-1β, TNFá and IFNΓ, but appreciable amounts of IL-6. The production of this later cytokine was, however, inhibited by the effect of progesterone. CONCLUSIONS : Basal production of IL-6 by DSC may be involved in physiological functions at the maternal-fetal interface. Nevertheless, the secretion of this cytokine is regulated by progesterone, probably to prevent excessive production of this cytokine from triggering an inflammatory response that might compromise pregnancy.     

Evaluation of cytokines in follicular fluid and their effect on fertilization and pregnancy outcome

Cytokines in follicular fluid (FF) are important for reproduction as they modulate oocyte maturation and ovulation which influence subsequent fertilization, development of early embryo and potential for implantation. We evaluated FF cytokines in women who underwent intracytoplasmic sperm injection (ICSI) and their association with fertilized oocytes, embryo quality and pregnancy outcome. FF belonging to 38 patients including 18 polycystic ovary (PCO) and 20 male/unexplained infertility patients were investigated for granulocyte colony stimulating factor (G-CSF), regulated upon activation normal T cell expressed and presumably secreted (RANTES), tumour necrosis factor (TNFα), interferon gamma (IFNγ) and interleukins (IL-4 and IL-2) by bead-based sandwich immunoassay. Our findings revealed that on the day of oocyte retrieval, G-CSF was positively correlated with the number of fertilized oocytes, while TNFα detection was associated with reduced number of fertilized oocytes. Only G-CSF showed significant positive effect to the pregnancy outcome although the cytokines studied were not associated with embryo quality. PCO as the cause of infertility did not show an association with cytokines in FF. The functions of cytokines in reproduction are likely to be complex, and cytokine evaluation may offer insight to the understanding of the mechanisms leading to success or failure of assisted reproduction.     

IL-6 and related cytokines as the critical lynchpins between inflammation and cancer

Inflammatory responses play pivotal roles in cancer development, including tumor initiation, promotion, progression, and metastasis. Cytokines are now recognized as important mediators linking inflammation and cancer, and are therefore potential therapeutic and preventive targets as well as prognostic factors. The interleukin (IL)-6 family of cytokines, especially IL-6 and IL-11, is highly up-regulated in many cancers and considered as one of the most important cytokine families during tumorigenesis and metastasis. This review discusses molecular mechanisms linking the IL-6 cytokine family to solid malignancies and their treatment.     

Immunological aspects of implantation and implantation failure

The human endometrium contains a significant proportion of leukocytes (8-35% of all cells), the absolute numbers and proportions varying during both the menstrual cycle and early in pregnancy. T cells, macrophages and a population of phenotypically unusual large granular lymphocytes (LGL) are commonly present, although B cells are absent. Relative T cell numbers decrease significantly in first trimester decidua, and hence are unlikely to play an important role in maintenance of human pregnancy, but T cells could be important in implantation where their relative numbers are greater. In addition to producing cytokines, local tissue macrophages may provide an immediate antigen non-specific host defence to infection. Most attention has, nevertheless, focused on a role for LGL in implantation and maintenance of pregnancy since, at the time of implantation, LGL comprise 70-80% of the total endometrial leukocyte population. Although endometrial LGL have been shown to express natural killer (NK) cell-type cytotoxicity against classical NK cell targets, such cytotoxicity against trophoblast is induced only after activation by interleukin (IL)-2. Selective expression of the unusual class I human leukocyte antigen (HLA) molecule, HLA-G, by extravillous cytotrophoblast may assist in protecting invasive cytotrophoblast from potential maternal NK cell attack, probably via interactions with killer inhibitory receptor molecules on LGL. Many cytokines have been demonstrated to be expressed at the maternal-fetal interface although, currently, in mice only two (IL-11 and leukaemia inhibitory factor) appear to be absolutely essential for successful pregnancy outcome. Immune effector cells and cytokines may also play a role in human pregnancy pathologies, such as recurrent early pregnancy loss.     

Intrathecal release of pro- and anti-inflammatory cytokines during stroke

A growing body of evidence points out the potential role of inflammatory mechanisms in the pathophysiology of ischaemic brain damage. We have recently demonstrated that stroke patients display an intrathecal production of proinflammatory cytokines, such as IL-1β and IL-6 already within the first 24 h after the beginning of symptoms (Tarkowski et al., 1995). The aim of the present study was to investigate patterns of local inflammatory responses as a consequence of acute stroke. Thirty stroke patients were studied prospectively on days 0–3, 7–9, 21–26 and after day 90 with clinical evaluations, radiological assessments and analysis of cerebrospinal fluid (CSF) cytokine levels. In addition, 15 healthy control CSF samples were used. Significantly increased CSF levels of IL-8, granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-10 were observed early during the stroke with a peak on day 2 for the proinflammatory cytokines IL-8 and GM-CSF, and on day 3 for the immunoregulatory cytokine IL-10. Patients with a brain infarct predominantly located in the white matter showed significantly higher levels of IL-8 in CSF than patients with an infarct mainly located in the grey matter. Also, high levels of intrathecal tumour necrosis factor-alpha (TNF-α) were associated with the presence of white matter disease. Our study demonstrates an intrathecal production of proinflammatory and immunoregulatory cytokines in patients with stroke, supporting the notion of localized immune response to the acute brain lesion. A better understanding of the inflammatory response in stroke may lead to new treatment strategies.     

T-cell cytokines in pregnancy

PROBLEM: Immunological mechanisms induced by T cells may play an important role in preimplantation embryo development, in implantation process and in the phenomenon of fetal allograft tolerance. METHODS: We review existing data on the role of T cells in pregnancy. RESULTS: The production of LIF, interleukin (IL)-4, IL-10 and M-CSF by the decidual T cells may contribute to the maintenance of pregnancy. T cells are not only confined to the uterus. T cells are also present in cumulus oophorus and are able to produce LIF and IL-4. CONCLUSIONS: These findings may provide an initial cue in favor of the possibility that different cytokines produced by T cells acting in concert are required to create a suitable microenvironment for the preimplantation embryo development and for the maintenance of pregnancy. T cells could work in parallel with other cells present in the decidua and cumulus suggesting a complex network of hormones, cytokines and cells.     

Interleukin-13: Targeting an underestimated cytokine in atopic dermatitis

Atopic dermatitis (AD) is a common inflammatory skin condition that has traditionally been considered a paradigmatic type 2 immunity (T2)-driven disease. Interleukin (IL)-4 and IL-13 are both pivotal cytokines involved in the generation of allergic diseases. Currently, besides dupilumab, which blocks the binding of both cytokines to their receptors, a number of new pharmacologic entities have been designed to target both T2 cytokines and/or their receptors and/or receptor-associated signal transduction machinery such as Janus kinases. Recently, IL-13 has been suggested to be the key T2 cytokine driving inflammation in the periphery, while IL-4 may merely have a central effect. There is increasing evidence that this concept holds true for the inflammatory reaction underlying AD, where IL-13 is overexpressed locally and has a significant impact on skin biology, including the recruitment of inflammatory cells, the alteration of the skin microbiome, and the decrease in the epidermal barrier function. This review provides an update on the role of IL-13 in AD and discusses the different strategies aimed at interfering with its biologic activity as well as their potential in a precision medicine approach in the management of AD.     

Gene polymorphism of IL-6 and MMP-3 decreases passive range of motion after rotator cuff repair

Objectives: Post-operative stiffness is common after rotator cuff repair, given the difference in susceptibility and severity, the genetic factors may be involved. Interleukin 6 (IL-6) and Matrix metalloproteinases 3 (MMP-3) were previous found as key cytokines in the pathologies of adhesive capsulitis. The present study aims to investigate whether variants within the IL-6 and MMP-3 gene contributed to post-operative stiffness in a Chinese Han population. Methods: A total of 188 patients diagnosed with rotator cuff tears treated with mini-open surgery were enrolled in this study, among which 87 patients were diagnosed as post-operative stiffness and the remaining 101 patients as controls. All subjects were genotyped for IL-6 and MMP-3 SNPs. Results: The rs1800796 of IL-6 and rs679620 of MMP-3 were found significantly associated with increased susceptibility and severity of post-operative stiffness. Conclusion: The rs1800796 SNP of IL-6 and rs650108 SNP of MMP-3 were associated with increased risk of post-operative stiffness susceptibility and severity. This finding can be used in guiding the rehabilitation procedure after rotator cuff surgery, in another word, those with the genetic susceptibility factors should receive a more radical rehabilitation procedure and those without the susceptibility factors can be more conservative.     

Circulating IL-6, IL-17 and vitamin D in hepatocellular carcinoma: Potential biomarkers for a more favorable prognosis?

Abstract

Hepatitis C virus (HCV) infects primarily hepatocytes, leads to development of fibrosis and/or cirrhosis of the liver and is a significant factor for developing hepatocellular carcinoma (HCC). Evidence indicates that liver fibrosis contains uncontrolled inflammation as a part of its etiology. Normal cell-mediated immunity plays a central role in the mechanisms involved in viral clearance/persistence in the liver. In this context, cytokines modulate the immune system and exert direct anti-viral activity. To this end, this study investigated potential associations of serum IL-17 and IL-6 with exacerbation of hepatic damage in chronic HCV patients to determine their utility as prognostic markers for potential development of HCC. Chronic HCV-patients were recruited, divided into groups according to degree of liver damage, i.e. patients with peri-hepatic fibrosis, hepatic cirrhosis, or HCC, and had their blood collected for analysis of liver function and serum IL-6 and IL-17 levels. Interestingly, increases in serum IL-17 levels in the study groups were associated with aggravation of the clinical state from HCV to cirrhosis and then to HCC. Serum IL-6 levels followed a similar pattern. The association of both cytokines with progressive exacerbation of the initial HCV-induced liver damage was further confirmed by correlation analysis that revealed positive correlations between HCV RNA titer and IL-17 (+0.951, p?<?0.05) and IL-6 (+0.85, p?<?0.05). A receiver operating characteristics (ROC) analysis revealed their beneficial addition as promising biomarkers for a better prognostic profile of HCC. Interestingly, a significant progressive decline in the active vitamin D status was noted in all three clinical states, and these too were associated with progressive liver disease. This study confirms the necessity of adding screening for IL-6 and IL-17 and vitamin D to that of the classic marker AFP for patients with HCV and cirrhosis to hopefully permit clinicians to initiate measures that ultimately might mitigate/delay development of HCC in these infected patients.     

Interleukin-35: odd one out or part of the family?

Summary: Advances in cytokine biology have helped us understand the complex communication that takes place between antigen-presenting cells and cells of the adaptive immune system, such as T cells, which collectively mediate an appropriate immune response to a plethora of pathogens while maintaining tolerance to self-antigens. The interleukin-12 (IL-12) cytokine family remains one of the most important and includes IL-12, IL-23, IL-27, and the recently identified IL-35. All four are heterodimeric cytokines, composed of an α chain (p19, p28, or p35) and a β chain (p40 or Ebi3), and signal through unique pairings of five receptor chains (IL-12Rβ1, IL-12Rβ2, IL-23R, gp130, and WSX-1). Despite the interrelationship between the cytokines themselves and their receptors, their source, activity, and kinetics of expression are quite different. Studies using genetically deficient mice have greatly enhanced our understanding of the biology of these cytokines. However, interpretation of these data has been complicated by the recent realization that p40^−/−, p35^−/−, and Ebi3^−/− mice all lack more than one cytokine (IL-12/IL-23, IL-12/IL-35, and IL-27/IL-35, respectively). In this review, we compare and contrast the biology of this expanded IL-12 family and re-evaluate data derived from the analysis of these dual cytokine-deficient mice. We also discuss how the opposing characteristics of the IL-12 family siblings may help to promote a balanced immune response.