Homologues of human macrophage migration inhibitory factor from a parasitic nematode. Gene cloning, protein activity, and crystal structure

WISP1 induces the expression of macrophage migration inhibitory factor in human lung fibroblasts through Src kinases and EGFR-activated signaling pathways

Wnt1-inducible signaling protein 1 (WISP1/CCN4) is a secreted matricellular protein that is implicated in lung and airway remodeling. The macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that has been associated with chronic lung diseases. In this study, we aimed to investigate the WISP1 signaling pathway and its ability to induce the expression of MIF in primary cultures of fibroblasts from normal human lungs (HLFs). Our results showed that WISP1 significantly stimulated the expression of MIF in a concentration- and time-dependent fashion. In WISP1-induced expression of MIF, αvβ5-integrin and chondroitin sulfate proteoglycans as well as Src tyrosine kinases, MAP kinases, phosphatidylinositol 3-kinase/Akt, PKC, and NF-κB were involved. WISP1-induced expression of MIF was attenuated in the presence of the Src kinase inhibitor PP2 or the MIF tautomerase activity inhibitor ISO-1. Moreover, WISP1 significantly increased the phosphorylation and activation of EGF receptor (EGFR) through transactivation by Src kinases. WISP1 also induced the expression of MIF receptor CD74 and coreceptor CD44, through which MIF exerts its effects on HLFs. In addition, it was found that MIF induced its own expression, as well as its receptors CD74/CD44, acting in an autocrine manner. Finally, WISP1-induced MIF promoted the expression of cyclooxygenase 2, prostaglandin E2, IL-6, and matrix metalloproteinase-2 demonstrating the regulatory role of WISP1-MIF axis in lung inflammation and remodeling involving mainly integrin αvβ5, Src kinases, PKC, NF-κB, and EGFR. The specific signaling pathways involved in WISP1-induced expression of MIF may prove to be excellent candidates for novel targets to control inflammation in chronic lung diseases.NEW & NOTEWORTHY The present study demonstrates for the first time that Wnt1-inducible signaling protein 1 (WISP1) regulates migration inhibitory factor (MIF) expression and activity and identifies the main signaling pathways involved. The newly discovered WISP1-MIF axis may drive lung inflammation and could result in the design of novel targeted therapies in inflammatory lung diseases.

Macrophage Migration Inhibitory Factor (MIF) is a Key Player in Dry Eye Disease

PURPOSE

To explore the role of the proinflammatory cytokine, macrophage migration inhibitory factor (MIF), in a murine model of dry eye disease (DED).

METHODS

The role of MIF on DED was determined using genetically MIF deficient mice and pharmacological inhibition of MIF. DED was induced with 0.5 mg of scopolamine via subcutaneous injection in wild type (WT) and mice lacking MIF (Mif-/-), three times a day for 21 days. DED signs, tear volume, ferning pattern and cytology impression were evaluated. Also, eye tissues were collected to determine transcripts of key inflammatory mediators and histopathological damage. In a second set of experiments, we neutralized MIF with ISO-1, an isozaxiline-derivative MIF tautomerase activity-inhibiting small molecule in WT mice, following an acute DED model for 10 days. ISO-1 was given starting on day 3 after DED induction and signs were evaluated, including a recovery phase in both experimental approaches.

RESULTS

When compared to WT, Mif-/- mice showed attenuated signs of DED like preserved mucin pattern and increased tear volume. Also, Mif-/- mice maintained conjunctival epithelial cells and less corneal damage, associated with lower levels of TNFα and IL-1β. At recovery phase, Mif-/- mice presented improved signs. Interestingly, in cornea and conjunctiva the absence of MIF selectively downregulated the transcription of inflammatory enzymes like inos and nox4 whereas displayed enhanced transcripts of il-4, il-13, tgfβ and cox2. Finally, pharmacological inhibition of MIF using ISO-1, replicated the above findings in the mouse model.

CONCLUSION

MIF is a central positive mediator of the inflammatory process in experimental DED, thus, targeting MIF could be used as a novel therapy in ocular surface inflammatory pathologies.

The Immune Response to Nematode Infection

Nematode infection is a major threat to the health of humans, domestic animals and wildlife. Nematodes vary in their effect on the host and in the mechanisms underlying immunity but the general features are becoming clear. There is considerable variation among individuals in resistance to infection and much of this variation is due to genetic variation in the immune response. The major histocompatibility complex has a strong influence on resistance to infection but other genes are collectively more important. Resistant individuals produce more IgA, eosinophils, IgE and mast cells than susceptible individuals and this is a consequence of stronger type 2 (Th2) immune responses. A variety of factors promote Th2 responses including genetic background, diet, molecules produced by the parasite and the location of the infection. A variety of cells and molecules including proteins, glycolipids and RNA act in concert to promote responses and to regulate the response. Nematodes themselves also modulate the host response and over 20 parasite-derived immunomodulatory molecules have been identified. Different species of nematodes modulate the immune response in different ways and probably use multiple molecules. The reasons for this are unclear and the interactions among immunomodulators have still to be investigated.

A filarial parasite-encoded human IL-10 receptor antagonist reveals a novel strategy to modulate host responses

Interleukin (IL)-10 is the primary cytokine driving the modulation of the host response in filarial infections. We performed binding assays with Brugia malayi antigen extracts and human IL-10R1. Bm5539 was the top-binding hit. We identified a short sequence, termed truncated Bm5339, that has structural similarities to the human IL-10 functional dimer. Sequence comparisons revealed that other filarial parasites possess Bm5539 orthologues. Using recombinant Bm5539 in a modified Luciferase Immunoprecipitation System assay, we confirmed that both the truncated and full-length forms of the protein can bind to human IL-10R1. Truncated Bm5539 could inhibit human IL-10-driven phosphorylation of STAT3, thereby demonstrating that Bm5539 acts as an IL-10 antagonist, most likely through competitive binding to the receptor. We provide a structural basis for these observations using computational modeling and simulations. This parasite-encoded cytokine receptor antagonist provides an additional lens through which parasite-induced modulation of the host immune response can be examined.

Secreted filarial nematode galectins modulate host immune cells

Lymphatic filariasis (LF) is a mosquito-borne disease caused by filarial nematodes including Brugia malayi. Over 860 million people worldwide are infected or at risk of infection in 72 endemic countries. The absence of a protective vaccine means that current control strategies rely on mass drug administration programs that utilize inadequate drugs that cannot effectively kill adult parasites, thus established infections are incurable. Progress to address deficiencies in the approach to LF control is hindered by a poor mechanistic understanding of host-parasite interactions, including mechanisms of host immunomodulation by the parasite, a critical adaptation for establishing and maintaining infections. The canonical type 2 host response to helminth infection characterized by anti-inflammatory and regulatory immune phenotypes is modified by filarial nematodes during chronic LF. Current efforts at identifying parasite-derived factors driving this modification focus on parasite excretory-secretory products (ESP), including extracellular vesicles (EVs). We have previously profiled the cargo of B. malayi EVs and identified B. malayi galectin-1 and galectin-2 as among the most abundant EV proteins. In this study we further investigated the function of these proteins. Sequence analysis of the parasite galectins revealed highest homology to mammalian galectin-9 and functional characterization identified similar substrate affinities consistent with this designation. Immunological assays showed that Bma-LEC-2 is a bioactive protein that can polarize macrophages to an alternatively activated phenotype and selectively induce apoptosis in Th1 cells. Our data shows that an abundantly secreted parasite galectin is immunomodulatory and induces phenotypes consistent with the modified type 2 response characteristic of chronic LF infection.

Harnessing Immune Evasion Strategy of Lymphatic Filariae: A Therapeutic Approach against Inflammatory and Infective Pathology

Human lymphatic filariae have evolved numerous immune evasion strategies to secure their long-term survival in a host. These strategies include regulation of pattern recognition receptors, mimicry with host glycans and immune molecules, manipulation of innate and adaptive immune cells, induction of apoptosis in effector immune cells, and neutralization of free radicals. This creates an anti-inflammatory and immunoregulatory milieu in the host: a modified Th2 immune response. Therefore, targeting filarial immunomodulators and manipulating the filariae-driven immune system against the filariae can be a potential therapeutic and prophylactic strategy. Filariae-derived immunosuppression can also be exploited to treat other inflammatory diseases and immunopathologic states of parasitic diseases, such as cerebral malaria, and to prevent leishmaniasis. This paper reviews immunomodulatory mechanisms acquired by these filariae for their own survival and their potential application in the development of novel therapeutic approaches against parasitic and inflammatory diseases. Insight into the intricate network of host immune-parasite interactions would aid in the development of effective immune-therapeutic options for both infectious and immune-pathological diseases.

Parasitomimetics: Can We Utilize Parasite-Derived Immunomodulatory Molecules for Interventions to Immunological Disorders?

Because our immune system has ability to expel microorganisms invading our body, parasites need evolution to maintain their symbiosis with the hosts. One such strategy of the parasites is to manipulate host immunity by producing immunomodulatory molecules and the ability of parasites to regulate host immunity has long been a target of research. Parasites can not only manipulate host immune response specific to them, but also influence the host's entire immune system. Such ability of the parasites may sometimes bring benefit to the hosts as many studies have indicated the "hygiene hypothesis" that a decreased opportunity of parasitic infections is associated with an increased incidence of allergy and autoimmune diseases. In other words, elucidating the mechanisms of parasites to regulate host immunity could be applied not only to resolution of parasitic infections but also to treatment of non-parasitic immunological disorders. In this review, we show how much progress has been made in the research on immunomodulation of host immunity by parasites. Here, we define the word 'parasitomimetics' as emulation of parasites' immunomodulatory systems to solve immunological problems in humans and discuss potential applications of parasite-derived molecules to other diseases.

Nematode Orthologs of Macrophage Migration Inhibitory Factor (MIF) as Modulators of the Host Immune Response and Potential Therapeutic Targets

One of the adaptations of nematodes, which allows long-term survival in the host, is the production of proteins with immunomodulatory properties. The parasites secrete numerous homologs of human immune mediators, such as macrophage migration inhibitory factor (MIF), which is a substantial regulator of the inflammatory immune response. Homologs of mammalian MIF have been recognized in many species of nematode parasites, but their role has not been fully understood. The application of molecular biology and genetic engineering methods, including the production of recombinant proteins, has enabled better characterization of their structure and properties. This review provides insight into the current state of knowledge on MIF homologs produced by nematodes, as well as their structure, enzymatic activity, tissue expression pattern, impact on the host immune system, and potential use in the treatment of parasitic, inflammatory, and autoimmune diseases.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Recombinant Toxoplasma gondii MIF, CDPK3, and 14-3-3 Protein Cocktail Vaccine

Toxoplasma gondii can infect almost all endotherm organisms including humans and cause life-threatening toxoplasmosis in immunocompromised individuals, which leads to serious public health problems. Developing an excellent vaccine against this disease is impending. In present study, we formulated a cocktail protein vaccine including the TgMIF, TgCDPK3, and Tg14-3-3 proteins, which play critical roles in T. gondii infection. The recombinant protein vaccines were constructed and assessed by vaccination in BALB/c mice. We organized the mice in various protein combination groups of vaccines, and all mice were immunized with corresponding proteins at 0, 2, and 4 weeks. The specific protective effects of the vaccines on mice against T. gondii were analyzed by the mensuration of cytokines, serum antibodies, splenocyte proliferation assay, survival time, and parasite cyst burden of mice after the challenge. The study indicated that mice immunized with all three multicomponent proteins vaccine triggered a strong immune response with highest levels of IFN-γ production and IgG antibody compared with the other two protein combinations and controls. Moreover, there was an increase in IL-4 production and antigen-specific lymphocyte proliferation. The parasite cysts were significantly reduced (resulting in an 82.7% reduction), and survival time was longer in immunized mice with three multicomponent proteins compared with the other groups of mice. The enhanced humoral and cell-mediated immunity indicated that the protein cocktail vaccine containing three antigens provided effective protection for mice. These results indicated that recombinant TgMIF, TgCDPK3, and Tg14-3-3 multicomponent proteins were potential candidates for vaccine against toxoplasmosis.

Macrophage migration inhibitory factor in Nodding syndrome

Nodding syndrome (NS) is a catastrophic and enigmatic childhood epilepsy, accompanied by multiple neurological impairments and neuroinflammation. Of all the infectious, environmental and psychological factors associated with NS, the major culprit is Onchocerca Volvulus (Ov)-a parasitic worm transmitted to human by blackflies. NS seems to be an 'Autoimmune Epilepsy' in light of the recent findings of deleterious autoimmune antibodies to Glutamate receptors and to Leiomodin-I in NS patients. Moreover, we recently found immunogenetic fingerprints in HLA peptide-binding grooves associate with protection or susceptibility to NS. Macrophage migration inhibitory factor (MIF) is an immune-regulatory cytokine playing a central role in modulating innate and adaptive immunity. MIF is also involved in various pathologies: infectious, autoimmune and neurodegenerative diseases, epilepsy and others. Herein, two functional polymorphisms in the MIF gene, a -794 CATT5-8 microsatellite repeat and a -173 G/C single-nucleotide polymorphism, were assessed in 49 NS patients and 51 healthy controls from South Sudan. We also measured MIF plasma levels in established NS patients and healthy controls. We discovered that the frequency of the high-expression MIF -173C containing genotype was significantly lower in NS patients compared to healthy controls. Interestingly however, MIF plasma levels were significantly elevated in NS patients than in healthy controls. We further demonstrated that the HLA protective and susceptibility associations are dominant over the MIF association with NS. Our findings suggest that MIF might have a dual role in NS. Genetically controlled high-expression MIF genotype is associated with disease protection. However, elevated MIF in the plasma may contribute to the detrimental autoimmunity, neuroinflammation and epilepsy.

Identification of infiltrating immune cell subsets and heterogeneous macrophages in the lesion microenvironment of hepatic cystic echinococcosis patients with different cyst viability

Human cystic echinococcosis (CE) is characterized by lesion microenvironment formation through gathering various immune cells, including macrophages. However, immune cell subsets and heterogeneous macrophages in CE lesion microenvironment are poorly defined. Massive infiltrating immune cells formed lesion microenvironment, among which CD4⁺T cells and CD19⁺B cells were predominant and CD68⁺ macrophages were more evident in patients with active cysts. Different degrees of liver fibrosis was observed in Peri-Lesion (PL) liver samples, which was more evident in patients with active cysts. Expression of both M1 and M2 macrophage markers was significantly increased in PL liver samples. Importantly, elevation of M1 macrophage markers was more obvious in patients with inactive cysts, whereas M2 macrophage markers represented dominant macrophage phenotype in patients with active cysts. Additionally, macrophage-derived MIF, TGF-β1 and ECM1 were also expressed at higher level in CE lesion microenvironment of patients with active cysts. Moreover, MIF was evidently enhanced in the serum of hepatic CE patients, which was also predominant in patients with active cysts. Correlation analysis demonstrated positive correlation between expression of macrophage-derived cytokines and liver fibrosis degree. Heterogeneous macrophages may play significant roles in liver fibrosis of CE lesion microenvironment through producing pro-fibrogenic cytokines.

The Role of MIF on Eosinophil Biology and Eosinophilic Inflammation

Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine that participates in innate and adaptive immune responses. MIF contributes to the resistance against infection agents, but also to the cellular and tissue damage in infectious, autoimmune, and allergic diseases. In the past years, several studies demonstrated a critical role for MIF in the pathogenesis of type-2-mediated inflammation, including allergy and helminth infection. Atopic patients have increased MIF amounts in affected tissues, mainly produced by immune cells such as macrophages, Th2 cells, and eosinophils. Increased MIF mRNA and protein are found in activated Th2 cells, while eosinophils stock pre-formed MIF protein and secrete high amounts of MIF upon stimulation. In mouse models of allergic asthma, the lack of MIF causes an almost complete abrogation of the cardinal signs of the disease including mucus secretion, eosinophilic inflammation, and airway hyper-responsiveness. Additionally, blocking the expression of MIF in animal models leads to significant reduction of pathological signs of eosinophilic inflammation such as rhinitis, atopic dermatitis, eosinophilic esophagitis and helminth infection. A number of studies indicate that MIF is important in the effector phase of type-2 immune responses, while its contribution to Th2 differentiation and IgE production is not consensual. MIF has been found to intervene in different aspects of eosinophil physiology including differentiation, survival, activation, and migration. CD4+ T cells and eosinophils express CD74 and CXCR4, receptors able to signal upon MIF binding. Blockage of these receptors with neutralizing antibodies or small molecule antagonists also succeeds in reducing the signals of inflammation in experimental allergic models. Together, these studies demonstrate an important contribution of MIF on eosinophil biology and in the pathogenesis of allergic diseases and helminth infection.

What Can Parasites Tell Us About the Pathogenesis and Treatment of Asthma and Allergic Diseases

The same mechanisms that enable host defense against helminths also drive allergic inflammation. This suggests that pathomechanisms of allergic diseases represent evolutionary old responses against helminth parasites and that studying antihelminth immunity may provide insights into pathomechanisms of asthma. However, helminths have developed an intricate array of immunoregulatory mechanisms to modulate type 2 immune mechanisms. This has led to the hypothesis that the lack of helminth infection may contribute to the rise in allergic sensitization in modern societies. Indeed, the anti-inflammatory potential of helminth (worm) parasites and their products in allergy and asthma has been recognized for decades. As helminth infections bring about multiple undesired effects including an increased susceptibility to other infections, intended helminth infection is not a feasible approach to broadly prevent or treat allergic asthma. Thus, the development of new helminth-based biopharmaceutics may represent a safer approach of harnessing type 2–suppressive effects of helminths. However, progress regarding the mechanisms and molecules that are employed by helminths to modulate allergic inflammation has been relatively recent. The scavenging of alarmins and the modulation of lipid mediator pathways and macrophage function by helminth proteins have been identified as important immunoregulatory mechanisms targeting innate immunity in asthma and allergy. In addition, by regulating the activation of dendritic cells and by promoting regulatory T-cell responses, helminth proteins can counterregulate the adaptive T helper 2 cell response that drives allergic inflammation. Despite these insights, important open questions remain to be addressed before helminth molecules can be used for the prevention and treatment of asthma and other allergic diseases.

Structural and functional insights into macrophage migration inhibitory factor from Oncomelania hupensis, the intermediate host of Schistosoma japonicum

Oncomelania hupensis is the unique intermediate host of Schistosoma japonicum. As an irreplaceable prerequisite in the transmission and prevalence of schistosomiasis japonica, an in-depth study of this obligate host-parasite interaction can provide glimpse into the molecular events in the competition between schistosome infectivity and snail immune resistance. In previous studies, we identified a macrophage migration inhibitory factor (MIF) from O. hupensis (OhMIF), and showed that it was involved in the snail host immune response to the parasite S. japonicum. Here, we determined the crystal structure of OhMIF and revealed that there were distinct structural differences between the mammalian and O. hupensis MIFs. Noticeably, there was a projecting and structured C-terminus in OhMIF, which not only regulated the MIF's thermostability but was also critical in the activation of its tautomerase activity. Comparative studies between OhMIF and human MIF (hMIF) by analyzing the tautomerase activity, oxidoreductase activity, thermostability, interaction with the receptor CD74 and activation of the ERK signaling pathway demonstrated the functional differences between hMIF and OhMIF. Our data shed a species-specific light on structural, functional, and immunological characteristics of OhMIF and enrich the knowledge on the MIF family.

Wuchereria bancrofti macrophage migration inhibitory factor-2 (rWbaMIF-2) ameliorates experimental colitis

Immunomodulatory molecules produced by helminth parasites are receiving much attention recently as novel therapeutic agents for inflammation and autoimmune diseases. In this study, we show that macrophage migration inhibitory factor (MIF) homologue from the filarial parasite, Wuchereria bancrofti (rWbaMIF-2), can suppress inflammation in a dextran sulphate sodium salt (DSS)-induced colitis model. The disease activity index (DAI) in DSS given mice showed loss of body weight and bloody diarrhoea. At autopsy, colon of these mice showed severe inflammation and reduced length. Administration of rWbaMIF-2 significantly reduced the DAI in DSS-induced colitis mice. rWbaMIF-2-treated mice had no blood in the stools, and their colon length was similar to the normal colon with minimal inflammation and histological changes. Pro-inflammatory cytokine genes (TNF-α, IL-6, IFN-γ, IL-1β, IL-17A and NOS2) were downregulated in the colon tissue and peritoneal macrophages of rWbaMIF-2-treated mice. However, there were significant increases in IL-10-producing Treg and B1 cells in the colon and peritoneal cavity of rWbaMIF-2-treated mice. These findings suggested that rWbaMIF-2 treatment significantly ameliorated the clinical symptoms, inflammation and colon pathology in DSS given mice. This immunomodulatory effect of rWbaMIF-2 appeared to be by promoting the infiltration of Treg cells into the colon.

HcTTR: a novel antagonist against goat interleukin 4 derived from the excretory and secretory products of Haemonchus contortus

Haemonchus contortus (H. contortus) has evolved sophisticated evasion mechanisms to ensure their survival, including generating excretion and secretion products (ESPs) to regulate the secretion of host cytokines. Interleukin 4 (IL4) is a classic T-helper cell type 2 (Th2)-type cytokine that plays an irreplaceable role against nematode infection. In this study, three proteins, glutathione S-transferase domain containing protein (HcGST), transthyretin domain containing protein (HcTTR) and calponin actin-binding domain containing protein (HcCab), were identified to bind to goat IL4 by co-immunoprecipitation (Co-IP) assays and yeast two-hybrid screening. Additionally, cell proliferation analysis showed that HcTTR blocked the IL4-induced proliferation of peripheral blood mononuclear cells in goats, while HcGST and HcCab did not. In addition, HcTTR could also downregulate the transcription of candidate genes in the IL4-induced JAK/STAT pathway. These results indicated that HcTTR is a novel antagonist against goat IL4 from HcESPs, and this information could improve our understanding of the relationship between host cytokines and parasite infections.

Wuchereria bancrofti filaria activates human dendritic cells and polarizes T helper 1 and regulatory T cells via toll-like receptor 4

Interaction between innate immune cells and parasite plays a key role in the immunopathogenesis of lymphatic filariasis. Despite being professional antigen presenting cells critical for the pathogen recognition, processing and presenting the antigens for mounting T cell responses, the dendritic cell response and its role in initiating CD4+ T cell response to filaria, in particular Wuchereria bancrofti, the most prevalent microfilaria is still not clear. Herein, we demonstrate that a 70 kDa phosphorylcholine-binding W. bancrofti sheath antigen induces human dendritic cell maturation and secretion of several pro-inflammatory cytokines. Further, microfilarial sheath antigen-stimulated dendritic cells drive predominantly Th1 and regulatory T cell responses while Th17 and Th2 responses are marginal. Mechanistically, sheath antigen-induced dendritic cell maturation, and Th1 and regulatory T cell responses are mediated via toll-like receptor 4 signaling. Our data suggest that W. bancrofti sheath antigen exploits dendritic cells to mediate distinct CD4+ T cell responses and immunopathogenesis of lymphatic filariasis.

Protective Effect Against Toxoplasmosis in BALB/c Mice Vaccinated With Toxoplasma gondii Macrophage Migration Inhibitory Factor

Toxoplasma gondii is an obligate intracellular parasite responsible for toxoplasmosis, which can cause severe disease in the fetus and immunocompromised individuals. Developing an effective vaccine is crucial to control this disease. Macrophage migration inhibitory factor (MIF) has gained substantial attention as a pivotal upstream cytokine to mediate innate and adaptive immune responses. Homologs of MIF have been discovered in many parasitic species, and one homolog of MIF has been isolated from the parasite Toxoplasma gondii. In this study, the recombinant Toxoplasma gondii MIF (rTgMIF) as a protein vaccine was expressed and evaluated by intramuscular injection in BALB/c mice. We divided the mice into different dose groups of vaccines, and all immunizations with purified rTgMIF protein were performed at 0, 2, and 4 weeks. The protective efficacy of vaccination was analyzed by antibody assays, cytokine measurements and lymphoproliferative assays, respectively. The results obtained indicated that the rTgMIF vaccine elicited strong humoral and cellular immune responses with high levels of IgG antibody and IFN-γ production compared to those of the controls, in addition to slight higher levels of IL-4 production. After vaccination, a stronger lymphoproliferative response was also noted. Additionally, the survival time of mice immunized with rTgMIF was longer than that of the mice in control groups after challenge infection with virulent T. gondii RH tachyzoites. Moreover, the number of brain tissue cysts in vaccinated mice was reduced by 62.26% compared with the control group. These findings demonstrated that recombinant TgMIF protein is a potential candidate for vaccine development against toxoplasmosis.

Modulation of Host Immunity by Helminths: The Expanding Repertoire of Parasite Effector Molecules

Helminths are extraordinarily successful parasites due to their ability to modulate the host immune response. They have evolved a spectrum of immunomodulatory molecules that are now beginning to be defined, heralding a molecular revolution in parasite immunology. These discoveries have the potential both to transform our understanding of parasite adaptation to the host and to develop possible therapies for immune-mediated disease. In this review we will summarize the current state of the art in parasite immunomodulation and discuss perspectives on future areas for research and discovery.

Characterization of a secreted macrophage migration inhibitory factor homologue of the parasitic nematode Haemonchus Contortus acting at the parasite-host cell interface

Modulation and suppression of the immune response of the host by nematode parasites have been reported extensively and the migration inhibitory factor (MIF) is identified as one of the major immunomodulator. In the present study, we cloned and produced recombinant MIF protein from the small ruminant’s nematode parasite Haemonchus contortus (rHCMIF-1), and investigated its immunomodulatory effects on goat monocyte. Enzymatic assays indicated that rHCMIF-1 possessed tautomerase activity. Immunohistochemical test demonstrated that the native HCMIF-1 protein was predominantly localized at the body surface and internal surface of the worm’s gut. We demonstrated that rHCMIF-1 could be distinguished by antisera from goats experimentally infected with H. contortus and could bind by goat monocytes. The immunomodulatory effects of HCMIF-1 on cytokine secretion, MHC molecule expression, NO production and phagocytosis were observed by co-incubation of rHCMIF-1 with goat monocytes. The results showed that the interaction of rHCMIF-1 decreased the production of TNF-α, IL-1β and IL-12p40, where as, it significantly increased the secretion of IL-10 and TGF β in goat monocytes. After rHCMIF-1 exposure, the expression of MHC-II on goat monocytes was inhibited. Moreover, rHCMIF-1 could down-regulate the LPS induced NO production of goat monocytes. Phagocytotic assay by FITC-dextran internalization showed that rHCMIF-1 could inhibit the phagocytosis of goat monocytes. Our findings provided potential targetas immunoregulator, and will be helpful to elucidate the molecular basis of host–parasite interactions and search for new potential protein as vaccine and drug target candidate.

Differential immunomodulation in human monocytes versus macrophages by filarial cystatin

Parasitic nematodes have evolved powerful immunomodulatory molecules to enable their survival in immunocompetent hosts by subverting immune responses and minimizing pathological processes. One filarial molecule known to counteract host immune responses by inducing IL-10 and regulatory macrophages in mice is filarial cystatin. During a patent filarial infection monocytes encounter microfilariae in the blood, an event that occurs in asymptomatically infected filariasis patients that are immunologically hyporeactive. The microfilarial larval stage was formerly shown to induce human regulatory monocytes and macrophages. Thus, here we aim was to determine how filarial cystatin of the human pathogenic filaria Brugia malayi (BmCPI-2) contributes to immune hyporesponsiveness in human monocytes and macrophages elicited by microfilaria. For this purpose, filarial cystatin was depleted from microfilarial lysate (Mf). Detecting the immunomodulatory potential of cystatin-depleted Mf revealed that IL-10, but not IL-8 and IL-6 induction in monocytes and macrophages is dependent on the presence of cystatin. In addition, the Mf-induced expression of the regulatory surface markers PD-L1 and PD-L2 in human monocytes, but not in macrophages, is dependent on cystatin. While Mf-treated monocytes result in decreased CD4⁺ T-cell proliferation in a co-culture assay, stimulation of T-cells with human monocytes treated with cystatin-depleted Mf lead to a restoration of CD4⁺ T-cell proliferation. Moreover, IL-10 induction by cystatin within Mf was dependent on p38 and ERK in macrophages, but independent of the ERK pathway in monocytes. These findings indicate that filarial nematodes differentially trigger and exploit various signaling pathways to induce immunomodulation in different myeloid cell subsets.

Reprint of: The non-mammalian MIF superfamily

Macrophage migration inhibitory factor (MIF) was first described as a cytokine 50 years ago, and emerged in mammals as a pleiotropic protein with pro-inflammatory, chemotactic, and growth-promoting activities. In addition, MIF has gained substantial attention as a pivotal upstream mediator of innate and adaptive immune responses and with pathologic roles in several diseases. Of less importance in mammals is an intrinsic but non-physiologic enzymatic activity that points to MIF's evolution from an ancient defense molecule. Therefore, it is not surprising that mif-like genes also have been found across a range of different organisms including bacteria, plants, protozoa, helminths, molluscs, arthropods, fish, amphibians and birds. While Genebank analysis identifying mif-like genes across species is extensive, contained herein is an overview of the non-mammalian MIF-like proteins that have been most well studied experimentally. For many of these organisms, MIF contributes to an innate defense system or plays a role in development. For parasitic organisms however, MIF appears to function as a virulence factor aiding in the establishment or persistence of infection by modulating the host immune response. Consequently, a combined targeting of both parasitic and host MIF could lead to more effective treatment strategies for parasitic diseases of socioeconomic importance.

A computational assessment of the predicted structures of Human Macrophage Migration Inhibitory Factor 1 orthologs in parasites and its affinity to human CD74 receptor

The human macrophage migration inhibitory factor 1 (Hu-MIF-1) is a protein involved in the inflammatory and immunology response to parasite infection. In the present study, the existence of Hu-MIF-1 from parasites have been explored by mining WormBase. A total of 35 helminths were found to have Hu-MIF-1 homologs, including some parasites of importance for public health. Physicochemical, structural, and biological properties of Hu-MIF-1 were compared with its orthologs in parasites showing that most of these are secretory proteins, with positive net charge and presence of the Cys-Xaa-Xaa-Cys motif that is critical for its oxidoreductase activity. The inhibitor-binding site present in Hu-MIF-1 is well conserved among parasite MIFs suggesting that Hu-MIF inhibitors may target orthologs in pathogens. The binding of Hu-MIF-1 to its cognate receptor CD74 was predicted by computer-assisted docking, and it resulted to be very similar to the predicted complexes formed by parasite MIFs and human CD74. More than 1 plausible conformation of MIFs in the extracellular loops of CD74 may be possible as demonstrated by the different predicted conformations of MIF orthologs in complex with CD74. Parasite MIFs in complex with CD74 resulted with some charged residues oriented to CD74, which was not observed in the Hu-MIF-1/CD74 complex. Our findings predict the binding mode of Hu-MIF-1 and orthologs with CD74, which can assist in the design of novel MIF inhibitors. Whether the parasite MIFs function specifically subvert host immune responses to suit the parasite is an open question that needs to be further investigated. Future research should lead to a better understanding of parasite MIF action in the parasite biology.

Helminth Immunomodulation in Autoimmune Disease

Helminths have evolved to become experts at subverting immune surveillance. Through potent and persistent immune tempering, helminths can remain undetected in human tissues for decades. Redirecting the immunomodulating "talents" of helminths to treat inflammatory human diseases is receiving intensive interest. Here, we review therapies using live parasitic worms, worm secretions, and worm-derived synthetic molecules to treat autoimmune disease. We review helminth therapy in both mouse models and clinical trials and discuss what is known on mechanisms of action. We also highlight current progress in characterizing promising new immunomodulatory molecules found in excretory/secretory products of helminths and their potential use as immunotherapies for acute and chronic inflammatory diseases.

Structural characterization of As-MIF and hJAB1 during the inhibition of cell-cycle regulation

The biological activities of macrophage migration inhibitory factor (MIF) might be mediated through a classical receptor- mediated or non-classical endocytic pathway. JAB1 (C-Jun activation domain-binding protein-1) promotes the degradation of the tumor suppressor, p53, and the cyclin-dependent kinase inhibitor, p27. When MIF and JAB1 are bound to each other in various intracellular sites, MIF inhibits the positive regulatory effects of JAB1 on the activity of AP-1. The intestinal parasite, Anisakis simplex, has an immunomodulatory effect. The molecular mechanism of action of As-MIF and human JAB1 are poorly understood. In this study, As-MIF and hJAB1 were expressed and purified with high solubility. The structure of As-MIF and hJAB1 interaction was modeled by homology modeling based on the structure of Ace-MIF. This study provides evidence indicating that the MIF domain of As-MIF interacts directly with the MPN domain of hJAB1, and four structure-based mutants of As-MIF and hJAB1 disrupt the As-MIF-hJAB1 interaction.

The non-mammalian MIF superfamily

Macrophage migration inhibitory factor (MIF) was first described as a cytokine 50 years ago, and emerged in mammals as a pleiotropic protein with pro-inflammatory, chemotactic, and growth-promoting activities. In addition, MIF has gained substantial attention as a pivotal upstream mediator of innate and adaptive immune responses and with pathologic roles in several diseases. Of less importance in mammals is an intrinsic but non-physiologic enzymatic activity that points to MIF's evolution from an ancient defense molecule. Therefore, it is not surprising that mif-like genes also have been found across a range of different organisms including bacteria, plants, ‎protozoa, helminths, molluscs, arthropods, fish, amphibians and birds. While Genebank analysis identifying mif-like genes across species is extensive, contained herein is an overview of the non-mammalian MIF-like proteins that have been most well studied experimentally. For many of these organisms, MIF contributes to an innate defense system or plays a role in development. For parasitic organisms however, MIF appears to function as a virulence factor aiding in the establishment or persistence of infection by modulating the host immune response. Consequently, a combined targeting of both parasitic and host MIF could lead to more effective treatment strategies for parasitic diseases of socioeconomic importance.

Role of cysteine-58 and cysteine-95 residues in the thiol di-sulfide oxidoreductase activity of Macrophage Migration Inhibitory Factor-2 of Wuchereria bancrofti

Macrophage Migration Inhibitory Factor (MIF) is the first human cytokine reported and was thought to have a central role in the regulation of inflammatory responses. Homologs of this molecule have been reported in bacteria, invertebrates and plants. Apart from cytokine activity, it also has two catalytic activities viz., tautomerase and di-sulfide oxidoreductase, which appear to be involved in immunological functions. The CXXC catalytic site is responsible for di-sulfide oxidoreductase activity of MIF. We have recently reported thiol-disulfide oxidoreductase activity of Macrophage Migration Inhibitory Factor-2 of Wuchereria bancrofti (Wba-MIF-2), although it lacks the CXXC motif. We hypothesized that three conserved cysteine residues might be involved in the formation of di-sulfide oxidoreductase catalytic site. Homology modeling of Wba-MIF-2 showed that among the three cysteine residues, Cys58 and Cys95 residues came in close proximity (3.23Å) in the tertiary structure with pKa value 9, indicating that these residues might play a role in the di-sulfide oxidoreductase catalytic activity. We carried out site directed mutagenesis of these residues (Cys58Ser & Cys95Ser) and expressed mutant proteins in Escherichia coli. The mutant proteins did not show any oxidoreductase activity in the insulin reduction assay, thus indicating that these two cysteine residues are vital for the catalytic activity of Wba-MIF-2.

Looking beyond the induction of Th2 responses to explain immunomodulation by helminths

Although helminth infections are characteristically associated with Th2-mediated responses that include the production of the prototypical cytokines IL-4, IL-5 and IL-13 by CD4(+) cells, the production of IgE, peripheral blood eosinophilia and mucus production in localized sites, these responses are largely attenuated when helminth infections become less acute. This modulation of the immune response that occurs with chronic helminth infection is often induced by molecules secreted by helminth parasites, by non-Th2 regulatory CD4(+) cells, and by nonclassical B cells, macrophages and dendritic cells. This review will focus on those parasite- and host-mediated mechanisms underlying the modulated T-cell response that occurs as the default in chronic helminth infections.

Release of Small RNA-containing Exosome-like Vesicles from the Human Filarial Parasite Brugia malayi

Lymphatic filariasis (LF) is a socio-economically devastating mosquito-borne Neglected Tropical Disease caused by parasitic filarial nematodes. The interaction between the parasite and host, both mosquito and human, during infection, development and persistence is dynamic and delicately balanced. Manipulation of this interface to the detriment of the parasite is a promising potential avenue to develop disease therapies but is prevented by our very limited understanding of the host-parasite relationship. Exosomes are bioactive small vesicles (30-120 nm) secreted by a wide range of cell types and involved in a wide range of physiological processes. Here, we report the identification and partial characterization of exosome-like vesicles (ELVs) released from the infective L3 stage of the human filarial parasite Brugia malayi. Exosome-like vesicles were isolated from parasites in culture media and electron microscopy and nanoparticle tracking analysis were used to confirm that vesicles produced by juvenile B. malayi are exosome-like based on size and morphology. We show that loss of parasite viability correlates with a time-dependent decay in vesicle size specificity and rate of release. The protein cargo of these vesicles is shown to include common exosomal protein markers and putative effector proteins. These Brugia-derived vesicles contain small RNA species that include microRNAs with host homology, suggesting a potential role in host manipulation. Confocal microscopy shows J774A.1, a murine macrophage cell line, internalize purified ELVs, and we demonstrate that these ELVs effectively stimulate a classically activated macrophage phenotype in J774A.1. To our knowledge, this is the first report of exosome-like vesicle release by a human parasitic nematode and our data suggest a novel mechanism by which human parasitic nematodes may actively direct the host responses to infection. Further interrogation of the makeup and function of these bioactive vesicles could seed new therapeutic strategies and unearth stage-specific diagnostic biomarkers.

TLR2-dependent amelioration of allergic airway inflammation by parasitic nematode type II MIF in mice

In our previous studies, the recombinant type II macrophage migration inhibitory factor homologue (rAs-MIF) secreted from Anisakis simplex suppressed experimental inflammation mouse model through IL-10 production and CD4(+)CD25(+)Foxp3(+) T-cell recruitment. Also, TLR2 gene expression was significantly increased following rAs-MIF treatment. To know the relation between TLR2 and amelioration mechanisms of rAs-MIF, we induced allergic airway inflammation by ovalbumin and alum with or without rAs-MIF under TLR2 blocking systems [anti-TLR2-specific antibody (α-mTLR2 Ab) treatment and using TLR2 knockout mice]. As a result, the amelioration effects of rAs-MIF in allergic airway inflammation model (diminished inflammation and Th2 response in the lung, increased IL-10 secretion, CD4(+)CD25(+)Foxp3(+) T-cell recruitment) were diminished under two of the TLR2 blocking model. The expression of TLR2 on the surface of lung epithelial cell was significantly elevated by rAs-MIF treatment or Pam3CSK (TLR2-specific agonist) treatment, but they might have some competition effect on the elevation of TLR2 expression. In addition, the elevation of IL-10 gene expression by rAs-MIF treatment was significantly inhibited by α-mTLR2 Ab or Pam3CSK pretreatment. In conclusion, anti-inflammatory effects of the rAs-MIF on OVA-induced allergic airway inflammation might be closely related to TLR2.

Identification and biochemical characterization of macrophage migration inhibitory factor-2 (MIF-2) homologue of human lymphatic filarial parasite, Wuchereria bancrofti

Homologues of human macrophage migration inhibitory factor (hMIF) have been reported from vertebrates, invertebrates and prokaryotes, as well as plants. Filarial parasites produce two homologues of hMIF viz., MIF-1 and MIF-2, which play important role in the host immune modulation. Earlier, we have characterized MIF-1 (Wba-mif-1) from Wuchereria bancrofti, the major causal organism of human lymphatic filariasis. Here, we are reporting the molecular and biochemical characterization of MIF-2 from this parasite (Wba-mif-2). The complete Wba-mif-2 gene and its cDNA were amplified, cloned and sequenced. The size of Wba-mif-2 gene and cDNA were found to be 4.275 kb and 363 bp, respectively. The gene annotation revealed the presence of a large intron of 3.912 kb interspersed with two exons of 183 bp and 180 bp. The alignment of derived amino acid sequences of Wba-MIF-2 with Wba-MIF-1 showed 44% homology. The conserved CXXC oxido-reductase catalytic site present in Wba-mif-1 was found absent in Wba-mif-2 coding sequence. The amplified Wba-mif-2 cDNA was cloned into an expression vector pRSET-B and transformed into salt inducible Escherichia coli strain GJ1158. The expressed recombinant Wba-MIF-2 protein showed tautomerase activity against L-dopachrome methyl ester and the specific activity was determined to be 18.57±0.77 μmol/mg/min. Three known inhibitors of hMIF tautomerase activity significantly inhibited the tautomerase activity of recombinant Wba-MIF-2. Although the conserved CXXC oxido-reductase motif is absent in Wba-mif-2, the recombinant protein showed significant oxido-reductase activity in the insulin reduction assay, possibly because of the presence of vicinal cysteine residues.

Ostertagia ostertagi macrophage migration inhibitory factor is present in all developmental stages and may cross-regulate host functions through interaction with the host receptor

Macrophage migration inhibitory factor (MIF) of Ostertagia ostertagi, an abomasal parasite of cattle, was characterised in the present study. Phylogenetic analysis identified at least three O. ostertagi MIFs (Oos-MIFs), each encoded by a distinct transcript: Oos-MIF-1.1, Oos-MIF-1.2 and Oos-MIF-2. Oos-MIF-2 is only distantly related to Oos-MIF-1s, but has higher sequence similarity with the Caenorhabditis elegans MIF2. Oos-MIF-1.1 and Oos-MIF-1.2 are similar (93%) and thus collectively referred to as Oos-MIF-1 when characterised with immunoassays. Recombinant Oos-MIF-1.1 (rOos-MIF-1.1) is catalytically active as a tautomerase. A mutation (rOos-MIF-1.1P1G) or duplication of Pro1 residue (rOos-MIF-1.1P1+P) resulted in reduced oligomerisation and loss of tautomerase activity. The tautomerase activity of rOos-MIF-1.1 was only partially inhibited by ISO-1 but was abrogated by a rOos-MIF-1.1-specific antibody. Oos-MIF-1 was detected in all developmental stages of O. ostertagi, with higher levels in the adult stage; it was also detected in adult worm excretory/secretory product. Oos-MIF-1 was localised to the hypodermis/muscle, reproductive tract and intestine, but not to the cuticle. rOos-MIF-1.1, but not rOos-MIF-1.1P1G, was able to specifically bind to human CD74, a MIF cell surface receptor, with an affinity comparable with human MIF. Immunostaining indicated that macrophages were able to internalise rOos-MIF-1.1, further supporting receptor-mediated transportation. Herein we also show that rOos-MIF-1.1 inhibited migration of bovine macrophages and restored glucocorticoid-suppressed, lipopolysaccharide-induced TNF-α and IL-8 in human and/or bovine macrophages. Given its dual role in self-regulation and molecular mimicry, this secreted parasite protein warrants investigation as a vaccine candidate against O. ostertagi infections in cattle.

Biochemical and immunological characterization of Toxoplasma gondii macrophage migration inhibitory factor

Macrophage migration inhibitory factor (MIF) is a proinflammatory molecule in mammals that, unusually for a cytokine, exhibits tautomerase and oxidoreductase enzymatic activities. Homologues of this well conserved protein are found within diverse phyla including a number of parasitic organisms. Herein, we produced recombinant histidine-tagged Toxoplasma gondii MIF (TgMIF), a 12-kDa protein that lacks oxidoreductase activity but exhibits tautomerase activity with a specific activity of 19.3 μmol/min/mg that cannot be inhibited by the human MIF inhibitor ISO-1. The crystal structure of the TgMIF homotrimer has been determined to 1.82 Å, and although it has close structural homology with mammalian MIFs, it has critical differences in the tautomerase active site that account for the different inhibitor sensitivity. We also demonstrate that TgMIF can elicit IL-8 production from human peripheral blood mononuclear cells while also activating ERK MAPK pathways in murine bone marrow-derived macrophages. TgMIF may therefore play an immunomodulatory role during T. gondii infection in mammals.

Regulatory cells and immunosuppressive cytokines: parasite-derived factors induce immune polarization

Parasitic infections are prevalent in both tropical and subtropical areas. Most of the affected and/or exposed populations are living in developing countries where control measures are lacking or inadequately applied. Although significant progress has been made in our understanding of the immune response to parasites, no definitive step has yet been successfully done in terms of operational vaccines against parasitic diseases. Evidence accumulated during the past few years suggests that the pathology observed during parasitic infections is in part due to deregulation of normal components of the immune system, mainly cytokines, antibodies, and immune effector cell populations. A large number of studies that illustrate how parasites can modify the host immune system for their own benefit have been reported in both metazoan and protozoan parasites. The first line of defense against foreign organisms is barrier tissue such as skin, humoral factors, for instance the complement system and pentraxin, which upon activation of the complement cascade facilitate pathogen recognition by cells of innate immunity such as macrophages and DC. However, all the major groups of parasites studied have been shown to contain and/or to release factors, which interfere with both arms of the host immune system. Even some astonishing observations relate to the production by some parasites of orthologues of mammalian cytokines. Furthermore, chronic parasitic infections have led to the immunosuppressive environment that correlates with increased levels of myeloid and T suppressor cells that may limit the success of immunotherapeutic strategies based on vaccination. This minireview briefly analyzes some of the current data related to the regulatory cells and molecules derived from parasites that affect cellular function and contribute to the polarization of the immune response of the host. Special attention is given to some of the data from our laboratory illustrating the role of immunomodulatory factors released by protozoan parasites, in the induction and perpetuation of chronic disease.

Recombinant Brugia malayi pepsin inhibitor (rBm33) induced monocyte function and absence of apoptotic cell death: an in vitro study

The effect of recombinant Brugia malayi pepsin inhibitor (rBm33) on human monocytes/macrophages has been examined using THP-1 cells. THP-1 cells stimulated with rBm33 showed enhanced levels of expression of pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) and diminished levels of IL-12, iNOS and anti-inflammatory cytokine (IL-10) expression suggesting the predominant features of Th1 response. Phorbol-12-myristate-13-acetate (PMA) treated THP-1 cells stimulated with rBm33 and subsequent incubation with GFP expressing Escherichia coli (E. coli) for 2 h enhanced the uptake of E. coli. Nitric oxide (NO) levels measured in the supernatants of these cultures did not show significant changes. Apoptotic studies with Peripheral Blood Mononuclear Cells (PBMCs) from normal individuals stimulated with rBm33 did not induce apoptosis of monocytes or lymphocytes. These observations suggest that rBm33 stimulates macrophages to induce Th1 response and does not promote apoptosis.

Dermacentor variabilis: characterization and modeling of macrophage migration inhibitory factor with phylogenetic comparisons to other ticks, insects and parasitic nematodes

We have identified and characterized the full length cDNA sequence of macrophage migration inhibitory factor (MIF) from the American dog tick, Dermacentor variabilis. The nucleotide and putative amino acid sequences from this study shared a high level of sequence conservation with other tick MIFs. The bioinformatics analysis showed across species conservation of the MIF amino acid sequence in ticks, insects and nematodes. The multiple sequence alignment identified Pro 1, 3, 55; Thr 7, 112; Asn 8, 72; Ile 64, 96; Gly 65, 110, Ser 63 and Leu 87 amino acids to be highly conserved among the sequences selected for this study. Tick MIF does not have the oxidoreductase domain as found in MIFs from other animals suggesting that tick MIF is not capable of performing as an oxidoreductase. The phylogenetic analysis revealed that tick MIFs share a closer evolutionary proximity to parasitic nematode MIFs than to insect MIFs.

Modulation of specific and allergy-related immune responses by helminths

Helminths are master regulators of host immune responses utilising complex mechanisms to dampen host protective Th2-type responses and favour long-term persistence. Such evasion mechanisms ensure mutual survival of both the parasite and the host. In this paper, we present recent findings on the cells that are targeted by helminths and the molecules and mechanisms that are induced during infection. We discuss the impact of these factors on the host response as well as their effect in preventing the development of aberrant allergic inflammation. We also examine recent findings on helminth-derived molecules that can be used as tools to pinpoint the underlying mechanisms of immune regulation or to determine new anti-inflammatory therapeutics.

Evaluation of the immune response induced by DNA vaccines expressing MIF and MCD-1 genes ofTrichinella spiralisin BALB/c mice

Plasmids expressing macrophage migration inhibitory factor (MIF) ofTrichinella spiralis(TsMIF), multi-cystatin-like domain protein (MCD-1) ofT. spiralis(TsMCD-1), or co-expressingTsMIF andTsMCD-1 were constructed with a pVAX1 vector. Their ability to generate a protective immune response againstT. spiralisinfection was evaluated in BALB/c mice. Groups of mice were immunized twice at 2-week intervals with 100 μg of recombinant plasmids pVAX1-Tsmif, pVAX1-Tsmcd-1or pVAX1-Tsmif-Tsmcd-1. Control animals were immunized with phosphate-buffered saline (PBS) or blank vector plasmid. Specific antibody levels (IgG, IgG1, IgG2a, IgG2b, IgM, IgA, IgE) against the recombinant proteinTsMIF-TsMCD-1, serum cytokines (interferon (IFN)-γ, interleukin (IL)-4, IL-5, transforming growth factor (TGF)-β1 and IL-17) and CD4+/CD8+T cells were monitored. Challenge infection was performed 2 weeks following the second immunization and worm burden was assayed at 35 days post-challenge. Vaccination with pVAX1-Tsmifinduced moderate serum IFN-γ and increases of CD4+and CD8+T cells, but no specific immunoglobulin antibody response. Vaccination with pVAX1-Tsmcd-1induced a predominant Th1 antibody (IgG2a and IgG2b) response and strong levels of serum IFN-γ, and increases of CD4+T cells. Importantly, co-expression ofTsMIF andTsMCD-1 in DNA immunization produced more serum IFN-γ and markedly enhanced CD4+and CD8+T cells than the single DNA vaccine of the two genes. Challenge infection demonstrated that immunization with pVAX1-Tsmif-Tsmcd-1reduced worm burdens (by 23.17%;P < 0.05).

Characterization of a secreted macrophage migration inhibitory factor homologue of the parasitic nematode Strongyloides acting at the parasite-host cell interface

Strongyloidiasis is a tropical parasitosis characterized by an alternation between free-living and parasitic stages, and by long-term infection via autoinfection. Since invasion and evasion processes of helminth parasites are substantially attained by the involvement of excretory-secretory products, we identified and characterized the 13.5 kDa macrophage migration inhibitory factor (MIF)-like protein in Strongyloides ratti. Sra-MIF is mainly secreted from the infective stage larvae (iL3), while the transcript was found at lower levels in parasitic and free-living females. Sequence analysis of the full-length cDNA showed the highest homology to the human pathogen Strongyloides stercoralis, and both are related to the MIF type-2. Unlike other mif genes, the Sra-mif includes no intron. The protein was recombinantly expressed in Escherichia coli and purified. Sra-MIF exhibited no in vitro tautomerase activity. The exposure of Sra-MIF to the host immune system is confirmed by high IgG reactivities found in the hosts' sera following infection or immunization. Flow cytometric analysis indicated the binding of Sra-MIF to the monocytes/macrophage lineage but not to peripheral lymphocytes. After exposure to Sra-MIF, monocytes released IL-10 but not TNF-alpha suggesting the involvement of the secreted parasite MIF in host immune responses.

Distinct immunoregulatory properties of macrophage migration inhibitory factors encoded by Eimeria parasites and their chicken host

Macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine that plays an important role in host defense against a variety of microorganisms including protozoan parasites. Interestingly, some microbial pathogens also express a MIF-like protein, although its role in disease pathogenesis is not well understood. The aim of this study was to compare an Eimeria-encoded MIF (E.MIF) protein with chicken MIF (C.MIF) on the basis of their structural, immunological, and biological properties. E.MIF and C.MIF proteins, each with a glutathione S-transferase epitope tag, were expressed in Escherichia coli or COS-7 cells and purified by glutathione affinity chromatography. Rabbit antisera against the purified proteins demonstrated their mutual immunological cross-reactivity on Western blots, and immunolocalized intracellular native E.MIF to the Eimeria schizont, merozoite, and oocyst life cycle stages. HD11 chicken macrophages treated in vitro with C.MIF recombinant protein expressed increased levels of transcripts encoding interleukin-6 (IL-6), IL-17, and tumor necrosis factor superfamily member 15 (TNFSF15), but decreased levels of IL-8 transcripts, compared with cells treated with the PBS control; similar treatment with E.MIF only down-regulated IL-8 transcripts. Unlike recombinant E.MIF, C.MIF exhibited in vitro chemotactic activity for HD11 cells. Conversely, E.MIF, but not C.MIF, enhanced protection against experimental Eimeria infection, compared with the PBS control. These studies provide evidence for overlapping structural and antigenic properties, but distinct immunoregulatory roles, of E.MIF and C.MIF.

A macrophage migration inhibitory factor like oxidoreductase from pearl oyster Pinctada fucata involved in innate immune responses

Macrophage migration inhibitory factor (MIF) is an important cytokine and plays a crucial role as a pivotal regulator of innate immunity. In this study, a MIF cDNA was identified and characterized from the pearl oyster Pinctada fucata (designated as PoMIF). The full-length of PoMIF was 1544 bp and consisted of a 5'-untranslated region (UTR) of 45 bp, a 3'-UTR of 1139 bp with a polyadenylation signal (AATAAA) at 12 nucleotides upstream of the poly (A) tail. The open reading frame (ORF) of PoMIF was 360 bp which encoded a polypeptide of 120 amino acids with an estimated molecular mass of 13.3 kDa and a predicted pI of 6.1. SMART analysis showed that PoMIF contained the catalytic-sites P² and K³³ for tautomerase activity, a motif C⁵⁷GSV⁶⁰ for oxidoreductase activity and a MIF family signature D⁵⁵PCGSVEVYSIGALG⁶⁹. Homology analysis revealed that the PoMIF shared 40.3-65.5% similarity and 26.9-45.0% identity to other known MIF sequences. PoMIF mRNA was constitutively expressed in seven selected tissues of healthy pearl oysters, with the highest expression level in digestive gland. Eight hours after P. fucata was injected with Vibrio alginolyticus, the expression of PoMIF mRNA was significantly up-regulated in digestive gland, gills, hemocytes and intestine. The cDNA fragment encoding mature protein of PoMIF was subcloned to expression vector pRSET and transformed into Escherichia coli BL21 (DE3). The recombinant PoMIF (rPoMIF) was expressed and purified under optimized conditions. Function analysis showed that rPoMIF had oxidoreductase activity and could utilize dithiothreitol (DTT) as reductant to reduce insulin.

Gender-associated genes in filarial nematodes are important for reproduction and potential intervention targets

Background

A better understanding of reproductive processes in parasitic nematodes may lead to development of new anthelmintics and control strategies for combating disabling and disfiguring neglected tropical diseases such as lymphatic filariasis and onchocerciasis. Transcriptomatic analysis has provided important new insights into mechanisms of reproduction and development in other invertebrates. We have performed the first genome-wide analysis of gender-associated (GA) gene expression in a filarial nematode to improve understanding of key reproductive processes in these parasites.

Methodology/Principal Findings

The Version 2 Filarial Microarray with 18,104 elements representing ∼85% of the filarial genome was used to identify GA gene transcripts in adult Brugia malayi worms. Approximately 19% of 14,293 genes were identified as GA genes. Many GA genes have potential Caenorhabditis elegans homologues annotated as germline-, oogenesis-, spermatogenesis-, and early embryogenesis- enriched. The potential C. elegans homologues of the filarial GA genes have a higher frequency of severe RNAi phenotypes (such as lethal and sterility) than other C. elegans genes. Molecular functions and biological processes associated with GA genes were gender-segregated. Peptidase, ligase, transferase, regulator activity for kinase and transcription, and rRNA and lipid binding were associated with female GA genes. In contrast, catalytic activity from kinase, ATP, and carbohydrate binding were associated with male GA genes. Cell cycle, transcription, translation, and biological regulation were increased in females, whereas metabolic processes of phosphate and carbohydrate metabolism, energy generation, and cell communication were increased in males. Significantly enriched pathways in females were associated with cell growth and protein synthesis, whereas metabolic pathways such as pentose phosphate and energy production pathways were enriched in males. There were also striking gender differences in environmental information processing and cell communication pathways. Many proteins encoded by GA genes are secreted by Brugia malayi, and these encode immunomodulatory molecules such as antioxidants and host cytokine mimics. Expression of many GA genes has been recently reported to be suppressed by tetracycline, which blocks reproduction in female Brugia malayi. Our localization of GA transcripts in filarial reproductive organs supports the hypothesis that these genes encode proteins involved in reproduction.

Conclusions/Significance

Genome-wide expression profiling coupled with a robust bioinformatics analysis has greatly expanded our understanding of the molecular biology of reproduction in filarial nematodes. This study has highlighted key molecules and pathways associated with reproductive and other biological processes and identified numerous potential candidates for rational drug design to target reproductive processes.

Lymphatic filariasis is a neglected tropical disease that is caused by thread-like parasitic worms that live and reproduce in lymphatic vessels of the human host. There are no vaccines to prevent filariasis, and available drugs are not effective against all stages of the parasite. In addition, recent reports suggest that the filarial nematodes may be developing resistance to key medications. Therefore, there is an urgent need to identify new drug targets in filarial worms. The purpose of this study was to perform a genome-wide analysis of gender-associated gene transcription to improve understanding of key reproductive processes in filarial nematodes. Our results indicate that thousands of genes are differentially expressed in male and female adult worms. Many of those genes are involved in specific reproductive processes such as embryogenesis and spermatogenesis. In addition, expression of some of those genes is suppressed by tetracycline, a drug that leads to sterilization of adult female worms in many filarial species. Thus, gender-associated genes represent priority targets for design of vaccines and drugs that interfere with reproduction of filarial nematodes. Additional work with this type of integrated systems biology approach should lead to important new tools for controlling filarial diseases.

A macrophage migration inhibitory factor like gene from scallop Chlamys farreri: Involvement in immune response and wound healing

Macrophage migration inhibitory factor (MIF) is an evolutionarily ancient and highly conserved cytokine with multiple functions. In the present study, a MIF-like gene was cloned from Zhikong scallop Chlamys farreri (designated as CfMIF) based on expressed sequence tag (EST) analysis and rapid amplification of cDNA ends (RACE) approach. The full-length cDNA of CfMIF was of 2296bp, consisting of a 5' untranslated region (UTR) of 60bp, a 3' UTR of 1903bp with a poly(A) tail and an open reading frame (ORF) of 333bp encoded 111 amino acid residues with a calculated molecular mass of 12.6kDa and a theoretical isoelectric point of 5.63. The deduced amino acid sequence of CfMIF shared 27-50.5% similarity with those of other known MIFs. A conserved MIF domain was identified in the deduced amino acid sequence of CfMIF, and conserved proline(2) and lysine(33) were also found to be present in CfMIF. Phylogenetic analysis revealed that CfMIF is one of MIF members. The tissue distribution and temporal expression of CfMIF in hemocytes of scallop after lipopolysaccharide (LPS), peptidoglycan (PGN) and β-glucan stimulation were detected by real-time RT-PCR. CfMIF gene was ubiquitously expressed in six selected tissues of healthy scallops, with the higher expression levels in hepatopancreas, mantle and gill. In comparison with the control group, the expression of CfMIF mRNA in hemocytes was up-regulated significantly at 6h, 24h and 48h after LPS treatment, and at all time points after PGN and glucan treatment. The cDNA fragment encoding mature peptide of CfMIF was recombined and expressed in Escherichia coli BL21 (DE3) pLysS. The recombinant protein of CfMIF (rCfMIF) promoted sheep fibroblast migration into scraped spaces in vitro. These results generated from the present study encourage us to suggest that CfMIF was a novel member of MIF family, and it was involved in immune response and wound healing by promoting fibroblast migration.

Elevated levels of the Plasmodium yoelii homologue of macrophage migration inhibitory factor attenuate blood-stage malaria

The excessive production of proinflammatory cytokines plays a significant role in the pathogenesis of severe malaria. Mammalian macrophage migration inhibitory factor (MIF) (mMIF) is an immune mediator that promotes a sustained proinflammatory response by inhibiting the glucocorticoid-mediated downregulation of inflammation. In addition, Plasmodium parasites also encode a homologue of mammalian MIF that is expressed in asexual-stage parasites. We used the Plasmodium yoelii murine model to study the potential role of parasite-encoded MIF in the pathogenesis of malaria. Antibodies raised against purified, non-epitope-tagged P. yoelii MIF (PyMIF) were used to localize expression in trophozoite- and schizont-stage parasites and demonstrate extracellular release. In vitro, recombinant PyMIF was shown to actively induce the chemotaxis of macrophages but did not induce or enhance tumor necrosis factor alpha (TNF-α) production from peritoneal macrophages. To examine the role of parasite-derived PyMIF in vivo, two transgenic parasite lines that constitutively overexpress PyMIF were generated, one in a nonlethal P. yoelii 17X background [Py17X-MIF(+)] and the other in a lethal P. yoelii 17XL background [Py17XL-MIF(+)]. Challenge studies with transgenic parasites in mice showed that the increased expression of PyMIF resulted in a reduction in disease severity. Mice infected with Py17X-MIF(+) developed lower peak parasitemia levels than controls, while malaria-associated anemia was unaltered. Infection with Py17XL-MIF(+) resulted in a prolonged course of infection and a reduction in the overall mortality rate. Combined, the data indicate that parasite-derived MIF does not contribute significantly to immunopathology but, through its chemotactic ability toward macrophages, may attenuate disease and prolong infection of highly virulent parasite isolates.

Structural and functional characterization of a macrophage migration inhibitory factor homologue from the marine cyanobacterium Prochlorococcus marinus

Macrophage migration inhibitory factor (MIF) is a multifunctional mammalian cytokine, which exhibits tautomerase and oxidoreductase activity. MIF homologues with pairwise sequence identities to human MIF ranging from 31% to 41% have been detected in various cyanobacteria. The gene encoding the MIF homologue from the marine cyanobacterium Prochlorococcus marinus strain MIT9313 has been cloned and the corresponding protein (PmMIF) overproduced, purified, and subjected to functional and structural characterization. Kinetic and (1)H NMR spectroscopic studies show that PmMIF tautomerizes phenylenolpyruvate and (p-hydroxyphenyl)enolpyruvate at low levels. The N-terminal proline of PmMIF is critical for these reactions because the P1A mutant has strongly reduced tautomerase activities. PmMIF shows high structural homology with mammalian MIFs as revealed by a crystal structure of PmMIF at 1.63 A resolution. MIF contains a Cys-X-X-Cys motif that mediates oxidoreductase activity, which is lacking from PmMIF. Engineering of the motif into PmMIF did not result in oxidoreductase activity but increased the tautomerase activity 8-fold. The shared tautomerase activities and the conservation of the beta-alpha-beta structural fold and key functional groups suggest that eukaryotic MIFs and cyanobacterial PmMIF are related by divergent evolution from a common ancestor. While several MIF homologues have been identified in eukaryotic parasites, where they are thought to play a role in modulating the host immune response, PmMIF is the first nonparasitic, bacterial MIF-like protein characterized in detail. This work sets the stage for future studies which could address the question whether a MIF-like protein from a free-living bacterium possesses immunostimulatory features similar to those of mammalian MIFs and MIF-like proteins found in parasitic nematodes and protozoa.

A macrophage migration inhibitory factor-like tautomerase from Teladorsagia circumcincta (Nematoda: Strongylida)

A macrophage migration inhibitory factor (MIF)-like molecule, Tci-MIF-1, was isolated from Teladorsagia circumcincta and subjected to detailed characterization. A cDNA representing Tci-mif-1 was isolated following its identification in third-stage larvae (L3)-enriched cDNA population. Sequencing of the cDNA indicated a 348-bp open reading frame (ORF) with the closest orthologue being a MIF derived from the human hookworm Ancylostoma ceylanicum. Messenger RNA (mRNA) representing the Tci-MIF-1 transcript was detected in eggs, L3 and adult stages of T. circumcincta. The transcript was also present, but to a lesser extent in fourth-stage larvae (L4). Detection of Tci-MIF-1 protein in T. circumcincta developmental stages reflected the transcript levels identified by reverse transcriptase-PCR. Using immunohistochemistry, the Tci-MIF-1 protein was shown to have a diffuse distribution in L3 tissue, and in L4 and adult stages, the protein was localized to the nematode gut. A recombinant version of Tci-MIF-1 was produced, and enzymic assays indicated that this recombinant protein and a somatic extract of L3 possessed dopachrome tautomerase activity as has been observed previously in other MIF-like molecules. Neither native, purified Tci-MIF nor recombinant Tci-MIF-1 dramatically influenced the in vitro migration of sheep monocytes.

Involvement of the cytokine MIF in the snail host immune response to the parasite Schistosoma mansoni

We have identified and characterized a Macrophage Migration Inhibitory Factor (MIF) family member in the Lophotrochozoan invertebrate, Biomphalaria glabrata, the snail intermediate host of the human blood fluke Schistosoma mansoni. In mammals, MIF is a widely expressed pleiotropic cytokine with potent pro-inflammatory properties that controls cell functions such as gene expression, proliferation or apoptosis. Here we show that the MIF protein from B. glabrata (BgMIF) is expressed in circulating immune defense cells (hemocytes) of the snail as well as in the B. glabrata embryonic (Bge) cell line that has hemocyte-like features. Recombinant BgMIF (rBgMIF) induced cell proliferation and inhibited NO-dependent p53-mediated apoptosis in Bge cells. Moreover, knock-down of BgMIF expression in Bge cells interfered with the in vitro encapsulation of S. mansoni sporocysts. Furthermore, the in vivo knock-down of BgMIF prevented the changes in circulating hemocyte populations that occur in response to an infection by S. mansoni miracidia and led to a significant increase in the parasite burden of the snails. These results provide the first functional evidence that a MIF ortholog is involved in an invertebrate immune response towards a parasitic infection and highlight the importance of cytokines in invertebrate-parasite interactions.