Effects of interleukin 3, interleukin 4, and fibroblasts on cultures of human lung mast cells in bronchoalveolar lavage fluids

The effects of T cell factors, including interleukin (IL)-3 and IL-4, and fibroblasts on the growth and differentiation of human lung mast cells (MCs) obtained by bronchoalveolar lavage (BAL) were examined. The number of MCs identified by alcian blue-safranin staining was twice that of the control culture without conditioned medium (CM) when BAL cells were cultured for 2 weeks in RPMI 1640 containing 10% fetal calf serum and partially purified CM derived from PHA-stimulated lymphocytes. In the presence of both recombinant (r) IL-3 and rIL-4, the number of MCs was twice as high as the control without increase in the per-cell histamine content after 2 weeks' culture. In umbilical cord blood cultures, IL-3 plus IL-4 augmented basophilic cells about 20-fold more than the control when cultured for 2 weeks. In some cases, the percentage of safranin-positive MCs was about 2-5 fold greater, with 2-7 fold higher histamine content, when cultured for 10 days with CM and fibroblasts derived from human embryonic lung. However, in all BAL experiments, there was no increase in the total number of MCs after culture compared with the initial number of MCs, unlike the umbilical cord blood cultures. These results suggest that T cell factors, including IL-3 and IL-4, and fibroblasts may influence the phenotype and the survival of lung mast cells in BAL, whereas there was no evidence for the presence of MC precursors in BAL fluids.     

Differences in functional consequences and signal transduction induced by IL-3, IL-5, and nerve growth factor in human basophils

Previous studies have indicated a redundancy in the effects of the cytokines, IL-3, IL-5, and nerve growth factor (NGF) on acute priming of human basophils. In the current study, we have examined the effects of these three cytokines on 18-h priming for leukotriene C4 generation, their ability to induce Fc(epsilon)RIbeta mRNA expression, or their ability to sustain basophil viability in culture. We also examine a variety of the signaling steps that accompany activation with these cytokines. In contrast with the ability of IL-3 to alter secretagogue-mediated cytosolic calcium responses following 18-h cultures, 18-h treatment with IL-5 or NGF did not affect C5a-induced leukotriene C4 generation or alter C5a-induced intracellular Ca2+ concentration elevations. IL-3 and IL-5, but not NGF, induced Fc(epsilon)RIbeta mRNA expression and all three improved basophil viability in culture with a ranking of IL-3 > IL-5 > or = NGF. All three cytokines acutely activated the extracellular signal-regulated kinase pathway and the signaling elements that preceded extracellular signal-regulated kinase and cytosolic phospholipase A2 phosphorylation, consistent with their redundant ability to acutely prime basophils. However, only IL-3 and IL-5 induced Janus kinase 2 and STAT5 phosphorylation. This pattern of signal element activation among the three cytokines most closely matched their ability to induce expression of Fc(epsilon)RIbeta mRNA. Induction of the sustained calcium signaling that follows overnight priming with IL-3 appeared to be related to the strength of the early signals activated by these cytokines but the relevant pathway required was not identified. None of the signaling patterns matched the ability of the cytokines to promote basophil survival.     

Mast cell accumulation in glioblastoma with a potential role for stem cell factor and chemokine CXCL12

Glioblastoma multiforme (GBM) is the most common and malignant form of glioma with high mortality and no cure. Many human cancers maintain a complex inflammatory program triggering rapid recruitment of inflammatory cells, including mast cells (MCs), to the tumor site. However, the potential contribution of MCs in glioma has not been addressed previously. Here we report for the first time that MCs infiltrate KRas+Akt-induced gliomas, using the RCAS/TV-a system, where KRas and Akt are transduced by RCAS into the brains of neonatal Gtv-a- or Ntv-a transgenic mice lacking Ink4a or Arf. The most abundant MC infiltration was observed in high-grade gliomas of Arf-/- mice. MC accumulation could be localized to the vicinity of glioma-associated vessels but also within the tumor mass. Importantly, proliferating MCs were detected, suggesting that the MC accumulation was caused by local expansion of the MC population. In line with these findings, strong expression of stem cell factor (SCF), i.e. the main MC growth factor, was detected, in particular around tumor blood vessels. Further, glioma cells expressed the MC chemotaxin CXCL12 and MCs expressed the corresponding receptor, i.e. CXCR4, suggesting that MCs could be attracted to the tumor through the CXCL12/CXCR4 axis. Supporting a role for MCs in glioma, strong MC infiltration was detected in human glioma, where GBMs contained significantly higher MC numbers than grade II tumors did. Moreover, human GBMs were positive for CXCL12 and the infiltrating MCs were positive for CXCR4. In conclusion, we provide the first evidence for a role for MCs in glioma.     

Downregulation of hepatic stem cell factor by Vivo-Morpholino treatment inhibits mast cell migration and decreases biliary damage/senescence and liver fibrosis in Mdr2−/− mice

Primary sclerosing cholangitis (PSC) is characterized by increased mast cell (MC) infiltration, biliary damage and hepatic fibrosis. Cholangiocytes secrete stem cell factor (SCF), which is a chemoattractant for c-kit expressed on MCs. We aimed to determine if blocking SCF inhibits MC migration, biliary damage and hepatic fibrosis.MethodsFVB/NJ and Mdr2^−/− mice were treated with Mismatch or SCF Vivo-Morpholinos. We measured (i) SCF expression and secretion; (ii) hepatic damage; (iii) MC migration/activation and histamine signaling; (iv) ductular reaction and biliary senescence; and (v) hepatic fibrosis. In human PSC patients, SCF expression and secretion were measured. In vitro, cholangiocytes were evaluated for SCF expression and secretion. Biliary proliferation/senescence was measured in cholangiocytes pretreated with 0.1% BSA or the SCF inhibitor, ISK03. Cultured HSCs were stimulated with cholangiocyte supernatant and activation measured. MC migration was determined with cholangiocytes pretreated with BSA or ISK03 loaded into the bottom of Boyden chambers and MCs into top chamber.ResultsBiliary SCF expression and SCF serum levels increase in human PSC. Cholangiocytes, but not hepatocytes, from SCF Mismatch Mdr2^−/− mice have increased SCF expression and secretion. Inhibition of SCF in Mdr2^−/− mice reduced (i) hepatic damage; (ii) MC migration; (iii) histamine and SCF serum levels; and (iv) ductular reaction/biliary senescence/hepatic fibrosis. In vitro, cholangiocytes express and secrete SCF. Blocking biliary SCF decreased MC migration, biliary proliferation/senescence, and HSC activation.ConclusionCholangiocytes secrete increased levels of SCF inducing MC migration, contributing to biliary damage/hepatic fibrosis. Targeting MC infiltration may be an option to ameliorate PSC progression.     

Epigenetic histone modification by butyrate downregulates KIT and attenuates mast cell function

Short-chain fatty acid butyrate is produced from the bacterial fermentation of indigestible fiber in the intestinal lumen, and it has been shown to attenuate lung inflammation in murine asthma models. Mast cells (MCs) are initiators of inflammatory response to allergens, and they play an important role in asthma. MC survival and proliferation is regulated by its growth factor stem cell factor (SCF), which acts through the receptor, KIT. It has previously been shown that butyrate attenuates the activation of MCs by allergen stimulation. However, how butyrate mechanistically influences SCF signalling to impact MC function remains unknown. Here, we report that butyrate treatment triggered the modification of MC histones via butyrylation and acetylation, and inhibition of histone deacetylase (HDAC) activity. Further, butyrate treatment caused downregulation of SCF receptor KIT and associated phosphorylation, leading to significant attenuation of SCF-mediated MC proliferation, and pro-inflammatory cytokine secretion. Mechanistically, butyrate inhibited MC function by suppressing KIT and downstream p38 and Erk phosphorylation, and it mediated these effects via modification of histones, acting as an HDAC inhibitor and not via its traditional GPR41 (FFAR3) or GPR43 (FFAR2) butyrate receptors. In agreement, the pharmacological inhibition of Class I HDAC (HDAC1/3) mirrored butyrate's effects, suggesting that butyrate impacts MC function by HDAC1/3 inhibition. Taken together, butyrate epigenetically modifies histones and downregulates the SCF/KIT/p38/Erk signalling axis, leading to the attenuation of MC function, validating its ability to suppress MC-mediated inflammation. Therefore, butyrate supplementations could offer a potential treatment strategy for allergy and asthma via epigenetic alterations in MCs.     

Thiol-sensitive mast cell lines derived from mouse bone marrow respond to a mast cell growth-enhancing activity different from both IL-3 and IL-4

A series of permanent IL-3-dependent cell lines have been established from normal BALB/c or C3H bone marrow using alpha-thioglycerol-supplemented culture medium and PWM-stimulated spleen cell-conditioned medium as a source of IL-3. The cell lines and derivatives cloned in agar resembled "mucosal type" mast cells with respect to phenotypic and functional properties. In this report we demonstrate that in vitro growth of these mast cell lines was not only dependent on IL-3 and synergistically enhanced by IL-4, but in addition regulated by alpha-thioglycerol which could be replaced by 2-ME or cysteamine. We show that these thiol-sensitive mast cell lines respond to a mast cell growth enhancing activity (MEA) present in spleen cell-conditioned medium and acting in concert with IL-3. Partially purified MEA was not able to stimulate the growth of IL-3-dependent 32Dcl.23 cells, IL-2-dependent CTLL-2 cells or the mouse T cell line F4/4K.6 (L3T4+) adapted to grow in purified IL-4. Moreover, 11B11 hybridoma-derived anti-IL-4 mAb specifically neutralizing mouse Il-4 were unable to abolish the bioactivity of MEA. PWM, CSF-1, GM-CSF, IL-1, IL-2, IL-5, IL-6, IL-7, IFN-gamma, TGF-alpha, TNF-alpha, NGF, or EPO did not substitute for MEA in our standard proliferation assay.     

Functional nerve growth factor receptors on human B lymphocytes. Interaction with IL-2.

In addition to its neurotrophic activity, nerve growth factor (NGF) has been shown to interact with cells of the immune system. We have characterized the effects of NGF on human B cell proliferation and the regulation of NGF receptor expression on these cells. Nerve growth factor receptors were expressed on all tonsillar and peripheral blood B cells and this expression was increased upon activation of the cells. NGF augmented the mitogenic effect of the T-independent B cell mitogen, Staphylococcus aureus Cowan I strain, and provided a progression signal to competent B cells. The proliferative response was augmented when the progression signal provided by NGF was combined with that provided by IL-2 but not with IL-4. One effect of the interaction between NGF and IL-2 appears to occur at the receptor level, because each of these ligands increased the expression of the receptor for the other ligand, whereas IL-4 was without effect. These results demonstrate the expression of functional receptors on human B lymphocytes, the involvement of NGF in immuno-regulation, and indicate that NGF may act as a B cell growth factor.     

Glucocorticoid suppresses autocrine survival of mast cells by inhibiting IL-4 production and ICAM-1 expression

When mast cells are activated through their high affinity IgE receptors (FcepsilonRI), release of chemical mediators is followed by secretion of multiple cytokines. In this work, we report that IL-3-dependent mast cell line MC9 undergoes apoptosis when IL-3 is withdrawn. However, cross-linking of FcepsilonRI prevents apoptosis of MC9 by an autocrine mechanism, producing IL-3, IL-4, and GM-CSF. Although stimulated MC9 synthesizes mRNAs and proteins of these cytokines, secretion of endogenous IL-3 and GM-CSF is not enough for cell survival, whereas IL-4 itself does not have survival effect on MC9, but it induces cell aggregation by expressing LFA-1 and makes it reactive to endogenous growth factors. Addition of dexamethazone (DXM) to MC9 results in significant down-regulation of IL-4 mRNA in activated MC9. However, mRNA levels of IL-3 and GM-CSF are not changed by DXM. DXM also directly down-regulates the expression of ICAM-1 that is the high affinity ligand of LFA-1, by which the self-aggregation of MC9 is inhibited. Thus, glucocorticoids suppress autocrine survival of mast cells by inhibiting IL-4 production and ICAM-1 expression.     

Functional expression of neurokinin 1 receptors on mast cells induced by IL-4 and stem cell factor

It is widely accepted that neurokinin 1 (NK(1)) receptors are not generally expressed on mast cells but little is known about their expression in inflammation. The present study shows expression of NK(1) receptors on bone marrow-derived mast cells (BMMC) under the influence of IL-4 or stem cell factor (SCF). Highest expression was found when both cytokines are present. Six days of coculture with the cytokines IL-4 and SCF showed significant expression of NK(1) receptors (NK(1) receptor(+)/c-kit(+) BMMC; control: 7%, IL-4/SCF: 16%), while 12 days of cytokine coculture increased this expression to 37% positive cells. A longer coculture with IL-4 and SCF did not give an additional effect. Increased expression in IL-4/SCF-treated BMMC was further confirmed using Western blot analysis. Next, we demonstrated the functional relevance of NK(1) receptor expression for mast cell activation, resulting in an enhanced degranulation upon stimulation by substance P. BMMC activation was significantly diminished by the NK(1) receptor antagonist RP67580 (10 micro M) when stimulated with low concentrations of substance P. The inactive enantiomer RP65681 had no effect. In addition, BMMC cultured from bone marrow of NK(1) receptor knockout mice showed significantly decreased exocytosis to low concentrations of substance P. The present study clearly shows that NK(1) receptor-induced activation contributes significantly at low physiological substance P concentrations (<100 micro M). In conclusion, BMMC were shown to express NK(1) receptors upon IL-4/SCF coculture. This expression of NK(1) receptors has been demonstrated to be of functional relevance and leads to an increase in the sensitivity of BMMC to substance P.     

Human airway smooth muscle promotes human lung mast cell survival, proliferation, and constitutive activation: cooperative roles for CADM1, stem cell factor, and IL-6

The microlocalization of mast cells within specific tissue compartments is thought to be critical for the pathophysiology of many diverse diseases. This is particularly evident in asthma where they localize to the airway smooth muscle (ASM) bundles. Mast cells are recruited to the ASM by numerous chemoattractants and adhere through CADM1, but the functional consequences of this are unknown. In this study, we show that human ASM maintains human lung mast cell (HLMC) survival in vitro and induces rapid HLMC proliferation. This required cell-cell contact and occurred through a cooperative interaction between membrane-bound stem cell factor (SCF) expressed on ASM, soluble IL-6, and CADM1 expressed on HLMC. There was a physical interaction in HLMC between CADM1 and the SCF receptor (CD117), suggesting that CADM1-dependent adhesion facilitates the interaction of membrane-bound SCF with its receptor. HLMC-ASM coculture also enhanced constitutive HLMC degranulation, revealing a novel smooth muscle-driven allergen-independent mechanism of chronic mast cell activation. Targeting these interactions in asthma might offer a new strategy for the treatment of this common disease.     

Combined action of stem cell factor,leukemia inhibitory factor,and cAMP on in vitro proliferation of mouse primordial germ cells

In the present paper we investigated the effects of stem cell factor/mastocyte growth factor (SCF/MGF), leukemia inhibitory factor/differentiating inhibitory activity (LIF/DIA) (two growth factors known to affect primordial germ cell growth in vitro) and forskolin (FRSK) (an activator of adenylate cyclase in many cell types) alone or in combination on the survival and proliferation of primordial germ cells (PGCs) obtained from 8.5, 10.5, and 11.5 days post coitum (dpc) mouse embryos and cultured without pre-formed cell feeder layers. The results showed that both at 1 and 3 days of culture the addition of 100 ng/ml SCF, 20 μM FRSK, or in some instances 20 ng/ml LIF alone caused a significant increase of PGC number as compared with controls. The highest effects were obtained when SCF and/or LIF were used together with FRSK. Moreover, we found that FRSK elevated cAMP levels in purified 11.5 dpc PGCs and that this compound, but not SCF and LIF, stimulated PGC proliferation, as assessed by 5-bromo-2′-deoxyuridin (BrdU) incorporation. These results suggest a mechanism of combined action of cAMP with SCF and/or LIF in the control of proliferation of mouse PGCs in vitro. © 1993 Wiley-Liss, Inc.     

Growth factor synergism and antagonism in early neural crest development.

This review article focuses on data that reveal the importance of synergistic and antagonistic effects in growth factor action during the early phases of neural crest development. Growth factors act in concert in different cell lineages and in several aspects of neural crest cell development, including survival, proliferation, and differentiation. Stem cell factor (SCF) is a survival factor for the neural crest stem cell. Its action is neutralized by neurotrophins, such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and neurotrophin-3 (NT-3) through apoptotic cell death. In contrast, SCF alone does not support the survival of melanogenic cells (pigment cell precursors). They require the additional presence of a neurotrophin (NGF, BDNF, or NT-3). Fibroblast growth factor-2 (FGF-2) is an important promoter of proliferation in neuronal progenitor cells. In neural crest cells, fibroblast growth factor treatment alone does not lead to cell expansion but also requires the presence of a neurotrophin. The proliferative stimulus of the fibroblast growth factor - neurotrophin combination is antagonized by transforming growth factor beta-1 (TGFbeta-1). Moreover, TGFbeta-1 promotes the concomitant expression of neuronal markers from two cell lineages, sympathetic neurons and primary sensory neurons, indicating that it acts on a pluripotent neuronal progenitor cell. Moreover, the combination of FGF-2 and NT3, but not other neurotrophins, promotes expression or activation of one of the earliest markers expressed by presumptive sympathetic neuroblasts, the norepinephrine transporter. Taken together, these data emphasize the importance of the concerted action of growth factors in neural crest development at different levels and in several cell lineages. The underlying mechanisms involve growth-factor-induced dependence of the cells on other factors and susceptibility to growth-factor-mediated apoptosis.     

Neutralizing endogenous IL-6 renders mast cells of the MCT type from lung, but not the MCTC type from skin and lung, susceptible to human recombinant IL-4-induced apoptosis

Human cord blood-derived mast cells undergo apoptosis upon exposure to recombinant human (rh)IL-4 and become resistant to rhIL-4-induced apoptosis when cultured in the presence of rhIL-6. The current study extends these effects of rhIL-4 to different populations of human mast cells, namely fetal liver-derived mast cells, lung-derived mast cells, and skin-derived mast cells. Endogenous production of IL-6 appears to protect fetal liver-derived mast cells and those of the MC(T) phenotype from rhIL-4-mediated apoptosis, because neutralization of IL-6 renders these mast cells sensitive. In contrast, mast cells of the MC(TC) phenotype from skin and lung were resistant to IL-4-mediated apoptosis, even after neutralization of endogenous IL-6. MC(TC) cells were CD124(low), whereas those of the MC(T) cells were CD124(high). These observations extend the phenotypic differences between MC(T) and MC(TC) types of human mast cells to include different functional responses to IL-4.     

Modification of expression of stem cell factor by various cytokines.

The local production of stem cell factor (SCF) may be an important mechanism for regulating proliferation, differentiation, and migration of various cells bearing c-kit receptors, and might be susceptible to the cytokines that serve in inflammation and tissue repair. We have demonstrated that in three murine cell lines, Balb/3T3A31, MC3T3-E1, and C3H-2K, which constitutively produced SCF with different quantity, the SCF mRNA expression was greatly enhanced in response to basic fibroblast growth factor (bFGF) or transforming growth factor beta1 (TGF-beta1). The study was carried out by in situ hybridization utilizing nonradioactive oligonucleotide probes and quantitative image analysis. Leukemia inhibitory factor (LIF) or interleukin-4 (IL-4) moderately increased SCF mRNA in all cell lines, but IL-3 did not. The dot-blot enzyme-linked immunosorbent assay (ELISA) further confirmed that SCF protein production in these cell lines and bone marrow stromal cells was markedly enhanced by TGF-beta1, although TGF-beta1 suppressed the proliferation of all these cells. bFGF also enhanced the SCF production in these cell lines, but did not in bone marrow stromal cells, suggesting a difference in their susceptibility to the cytokine. Our results suggest that TGF-beta1 and bFGF potentially modulate the biological function of cells bearing c-kit receptors through the modulation of SCF production in fibroblasts.     

The BCL1 B lymphoma responds to IL-4, IL-5, and GM-CSF

Proliferation in vitro of the in vivo passaged murine B cell tumor line BCL1 has been used as a standard assay for mouse interleukin-5 (IL-5) for a number of years. We demonstrate that this line will also respond to human IL-5. The response to murine IL-5 is abrogated by transforming growth factor-beta and to a lesser extent by interferon-gamma. This suggests a possible regulatory role for these lymphokines in the proliferation of B cells induced by IL-5. Other purified recombinant lymphokines were also tested for their ability to induce BCL1 proliferation. The lymphokines IL-1, IL-2, IL-3, and IL-6 had no effect on the growth of BCL1. In contrast, IL-4 and more surprisingly granulocyte-macrophage colony-stimulating factor (GM-CSF) also induced proliferation of this cell. These effects could be inhibited by specific antibodies directed against the respective lymphokines. These data suggest that GM-CSF, as well as IL-4 and IL-5, may be yet another regulator of neoplastic and possibly even normal B-cell growth and differentiation.     

IL-9 enhances the growth of human mast cell progenitors under stimulation with stem cell factor

We examined the effects of IL-9 on human mast cell development from CD34(+) cord blood (CB) and peripheral blood cells in serum-deprived cultures. IL-9 apparently enhanced cell production under stimulation with stem cell factor (SCF) from CD34(+) CB cells. A great majority of the cultured cells grown with SCF + IL-9 became positive for tryptase at 4 wk. In methylcellulose cultures of CD34(+) CB cells, IL-9 increased both the number and size of mast cell colonies grown with SCF. Furthermore, SCF + IL-9 caused an exclusive expansion of mast cell colony-forming cells in a 2-wk liquid culture of CD34(+) CB cells, at a level markedly greater than for SCF alone. Clonal cell cultures and RT-PCR analysis showed that the targets of SCF + IL-9 were the CD34(+)CD38(+) CB cells rather than the CD34(+)CD38(-) CB cells. IL-9 neither augmented the SCF-dependent generation of progeny nor supported the survival of 6-wk-cultured mast cells. Moreover, there was no difference in the appearance of tryptase(+) cells and histamine content in the cultured cells between SCF and SCF + IL-9. The addition of IL-9 increased numbers of mast cell colonies grown with SCF from CD34(+) peripheral blood cells in children with or without asthma. It is of interest that mast cell progenitors of asthmatic patients responded to SCF + IL-9 to a greater extent than those of normal controls. Taken together, IL-9 appears to act as a potent enhancer for the SCF-dependent growth of mast cell progenitors in humans, particularly asthmatic patients.     

IL-4 modulation of CD4+CD25+ T regulatory cell-mediated suppression

Murine CD4(+)CD25(+) T regulatory (Treg) cells were cocultured with CD4(+)CD25(-) Th cells and APCs or purified B cells and stimulated by anti-CD3 mAb. Replacement of APCs by B cells did not significantly affect the suppression of CD4(+)CD25(-) Th cells. When IL-4 was added to separate cell populations, this cytokine promoted CD4(+)CD25(-) Th and CD4(+)CD25(+) Treg cell proliferation, whereas the suppressive competence of CD4(+)CD25(+) Treg cells was preserved. Conversely, IL-4 added to coculture of APCs, CD4(+)CD25(-) Th cells, and CD4(+)CD25(+) Treg cells inhibited the suppression of CD4(+)CD25(-) Th cells by favoring their survival through the induction of Bcl-2 expression. At variance, suppression was not affected by addition of IL-13, although this cytokine shares with IL-4 a receptor chain. When naive CD4(+)CD25(-) Th cells were replaced by Th1 and Th2 cells, cell proliferation of both subsets was equally suppressed, but suppression was less pronounced compared with that of CD4(+)CD25(-) Th cells. IL-4 production by Th2 cells was also inhibited. These results indicate that although CD4(+)CD25(+) Treg cells inhibit IL-4 production, the addition of IL-4 counteracts CD4(+)CD25(+) Treg cell-mediated suppression by promoting CD4(+)CD25(-) Th cell survival and proliferation.     

Mast cells rescue implantation defects caused by c-kit deficiency

Various physiologically relevant processes are regulated by the interaction of the receptor tyrosine kinase (c-Kit) and its ligand stem cell factor (SCF), with SCF known to be the most important growth factor for mast cells (MCs). In spite of their traditional role in allergic disorders and innate immunity, MCs have lately emerged as versatile modulators of a variety of physiologic and pathologic processes. Here we show that MCs are critical for pregnancy success. Uterine MCs presented a unique phenotype, accumulated during receptivity and expanded upon pregnancy establishment. Kit^W-sh/W-sh mice, whose MC deficiency is based on restricted c-Kit gene expression, exhibited severely impaired implantation, which could be completely rescued by systemic or local transfer of wild-type bone marrow-derived MCs. Transferred wild-type MCs favored normal implantation, induced optimal spiral artery remodeling and promoted the expression of MC proteases, transforming growth factor-β and connective tissue growth factor. MCs contributed to trophoblast survival, placentation and fetal growth through secretion of the glycan-binding protein galectin-1. Our data unveil unrecognized roles for MCs at the fetomaternal interface with critical implications in reproductive medicine.