Filarial antigens mediate apoptosis of human monocytes through Toll-like receptor 4

Modulatory functions of recombinant electron transfer flavoprotein α subunit protein from Haemonchus contortus on goat immune cells in vitro

Suppression and modulation of the host immune response to parasitic nematodes have been extensively studied. In the present study, we cloned and produced recombinant electron transfer flavoprotein α subunit (ETFα) protein from Haemonchus contortus (rHCETFα), a parasitic nematode of small ruminants, and studied the effect of this protein on modulating the immune response of goat peripheral blood mononuclear cells (PBMCs) and monocytes. Immunohistochemical tests verified that the HCETFα protein was localized mainly in the intestinal wall and on the body surface of worms. Immunoblot analysis revealed that rHCETFα was recognized by the serum of goats artificially infected with H. contortus. Immunofluorescence analysis indicated that rHCETFα bound to the surface of PBMCs. rHCETFα was co-incubated with goat PBMCs to observe the immunomodulatory effects exerted by HCETFα on proliferation, apoptosis, cytokine secretion and nitric oxide (NO) production. The results showed that rHCETFα suppressed the proliferation of goat PBMCs stimulated by concanavalin A and induced apoptosis in goat PBMCs. After rHCETFα exposure, IL-2, IL-4, IL-17A and TNF-α expression was markedly reduced, whereas secretion of TGF-β1 was significantly elevated, in goat PBMCs. Moreover, rHCETFα up-regulated NO production in a dose-dependent manner. FITC-dextran internalization assays showed that rHCETFα inhibited phagocytosis of goat monocytes. These results elucidate the interaction between parasites and hosts at the molecular level, suggest a possible immunomodulatory target and contribute to the search for innovative proteins that may be candidate targets for drugs and vaccines.

Characterization of a rhodanese homologue from Haemonchus contortus and its immune-modulatory effects on goat immune cells in vitro

BACKGROUND

Modulation of the host immune response by nematode parasites has been widely reported. Rhodaneses (thiosulfate: cyanide sulfurtransferases) are present in a wide range of organisms, such as archaea, bacteria, fungi, plants and animals. Previously, it was reported that a rhodanese homologue could be bound by goat peripheral blood mononuclear cells (PBMCs) in vivo.

METHODS

In the present study, we cloned and produced a recombinant rhodanese protein originating from Haemonchus contortus (rHCRD), a parasitic nematode of small ruminants. rHCRD was co-incubated with goat PBMCs to assess its immunomodulatory effects on proliferation, apoptosis and cytokine secretion.

RESULTS

We verified that the natural HCRD protein localized predominantly to the bowel wall and body surface of the parasite. We further demonstrated that serum produced by goats artificially infected with H. contortus successfully recognized rHCRD, which bound to goat PBMCs. rHCRD suppressed proliferation of goat PBMCs stimulated by concanavalin A but did not induce apoptosis in goat PBMCs. The production of TNF-α and IFN-γ decreased significantly, whereas secretion of IL-10 and TGF-β1 increased, in goat PBMCs after exposure to rHCRD. rHCRD also inhibited phagocytosis by goat monocytes. Moreover, rHCRD downregulated the expression of major histocompatibility complex (MHC)-II on goat monocytes in a dose-dependent manner, but did not alter MHC-I expression.

CONCLUSIONS

These results propose a possible immunomodulatory target that may help illuminate the interactions between parasites and their hosts at the molecular level and reveal innovative protein species as candidate drug and vaccine targets.

Characterization of a phosphotyrosyl phosphatase activator homologue of the parasitic nematode Haemonchus contortus and its immunomodulatory effect on goat peripheral blood mononuclear cells in vitro

Suppression and modulation of the host immune response to parasitic nematodes have been extensively studied. In the present study, we cloned and produced recombinant phosphotyrosyl phosphatase activator protein from Haemonchus contortus (rHCPTPA), a parasitic nematode of small ruminants, and studied the effect of this protein on modulating the immune response of goat peripheral blood mononuclear cells. Enzymatic assays revealed that rHCPTPA enhanced the p-nitrophenylphosphate phosphatase activity of bovine PP2A₁. Immunohistochemical tests verified that the HCPTPA protein was localised mainly in the bowel wall and on the body surface of worms. It was also shown that serum produced by goats artificially infected with H. contortus successfully recognised rHCPTPA, which conjugated with goat peripheral blood mononuclear cells. The rHCPTPA was then co-incubated with goat peripheral blood mononuclear cells to assess its immunomodulatory effects on proliferation, apoptosis, cytokine secretion, migration and nitric oxide production. Our results showed that rHCPTPA suppressed the proliferation of goat peripheral blood mononuclear cells stimulated by concanavalin A and induced apoptosis in goat peripheral blood mononuclear cells. After rHCPTPA exposure, IFN-γ and IL-2 expression was markedly reduced, whereas secretion of IL-10 and IL-4 was significantly elevated, in goat peripheral blood mononuclear cells. Moreover, rHCPTPA down-regulated nitric oxide production and migration of goat peripheral blood mononuclear cells in a dose-dependent manner. These results illuminate the interaction between parasites and hosts at the molecular level, suggest a possible immunomodulatory target and contribute to the search for innovative proteins that might be candidate targets for drugs and vaccines.

Anisakis pegreffii impacts differentiation and function of human dendritic cells

Human dendritic cells (DCs) show remarkable phenotypic changes when matured in the presence of helminth-derived products. These modifications frequently elicited a polarization towards Th2 cells and regulatory T cells thus contributing to immunological tolerance against these pathogens. In this study, the interaction between DCs and larvae of the zoonotic anisakid nematode Anisakis pegreffii was investigated. A. pegreffii larvae were collected from fish hosts, and monocyte-derived DCs were cocultured in the presence of the live larvae (L) or its crude extracts (CE). In both experimental conditions, A. pegreffii impacted DC viability, hampered DC maturation by reducing the expression of molecules involved in antigen presentation and migration (ie HLA-DR, CD86, CD83 and CCR7), increased the phagosomal radical oxygen species (ROS) levels and modulated the phosphorylation of ERK1,2 pathway. These biological changes were accompanied by the impairment of DCs to activate a T-cell-mediated IFNγ. Interestingly, live larvae appeared to differently modulate DC secretion of cytokines and chemokines as compared to CE. These results demonstrate, for the first time, the immunomodulatory role of A. pegreffii on DCs biology and functions. In addition, they suggest a dynamic contribution of DCs to the induction and maintenance of the inflammatory response against A. pegreffii.

Human innate lymphoid cells (ILCs) in filarial infections

Filarial infections are characteristically chronic and can cause debilitating diseases governed by parasite-induced innate and adaptive immune responses. Filarial parasites traverse or establish niches in the skin (migrating infective larvae), in nonmucosal tissues (adult parasite niche) and in the blood or skin (circulating microfilariae) where they intersect with the host immune response. While several studies have demonstrated that filarial parasites and their antigens can modulate myeloid cells (monocyte, macrophage and dendritic cell subsets), T- and B-lymphocytes and skin resident cell populations, the role of innate lymphoid cells during filarial infections has only recently emerged. Despite the identification and characterization of innate lymphoid cells (ILCs) in murine helminth infections, little is actually known about the role of human ILCs during parasitic infections. The focus of this review will be to highlight the composition of ILCs in the skin, lymphatics and blood; where the host-parasite interaction is well-defined and to examine the role of ILCs during filarial infections.

Surface proteins of Setaria cervi induce inflammation in macrophage through Toll-like receptor 4 (TLR4)-mediated signalling pathway

Lymphatic filariasis is a vectorborne parasitic disease that results in morbidities, disabilities and socio-economic loss each year globally. Inflammatory consequences associated with any form of filariasis have drawn special attention. However, the molecular insight behind the inflammation of host macrophage (MФ) is considered as one of the shaded areas in filarial research. Herein, major emphasis was given to study the signalling pathway of MФ inflammation induced by surface proteins (SPs) of filarial parasite through in vitro and in vivo approaches. Twenty-four hours of in vitro stimulation of Raw MФs with endotoxin-free SPs of Setaria cervi resulted in the secretion of pro-inflammatory cytokines (TNF-α and IL-1β) that revealed induction of inflammation, which was found to be elicited from classical NF-кB activation. Moreover, this NF-кB activation was found to be signalled from TLR4 and mediated by the downstream signalling intermediates, viz. MyD88, pTAK1 and NEMO. In vivo studies in adult Wistar rats, experimentally injected with SPs, clearly supported the outcomes of in vitro experiments by showing higher degree of inflammation rather classical activation of the peritoneal MФs. Therefore, SPs from S. cervi cuticle could be responsible for the induction of pro-inflammatory response in MФ, which appears to be propagated through TLR4-NF-кB route.

Pathological manifestations in lymphatic filariasis correlate with lack of inhibitory properties of IgG4 antibodies on IgE-activated granulocytes

Helminth parasites are known to be efficient modulators of their host's immune system. To guarantee their own survival, they induce alongside the classical Th2 a strong regulatory response with high levels of anti-inflammatory cytokines and elevated plasma levels of IgG4. This particular antibody was shown in different models to exhibit immunosuppressive properties. How IgG4 affects the etiopathology of lymphatic filariasis (LF) is however not well characterized. Here we investigate the impact of plasma and affinity-purified IgG/IgG4 fractions from endemic normals (EN) and LF infected pathology patients (CP), asymptomatic microfilaraemic (Mf+) and amicrofilaraemic (Mf-) individuals on IgE/IL3 activated granulocytes. The activation and degranulation states were investigated by monitoring the expression of CD63/HLADR and the release of granule contents (neutrophil elastase (NE), eosinophil cationic protein (ECP) and histamine) respectively by flow cytometry and ELISA. We could show that the activation of granulocytes was inhibited in the presence of plasma from EN and Mf+ individuals whereas those of Mf- and CP presented no effect. This inhibitory capacity was impaired upon depletion of IgG in Mf+ individuals but persisted in IgG-depleted plasma from EN, where it strongly correlated with the expression of IgA. In addition, IgA-depleted fractions failed to suppress granulocyte activation. Strikingly, affinity-purified IgG4 antibodies from EN, Mf+ and Mf- individuals bound granulocytes and inhibited activation and the release of ECP, NE and histamine. In contrast, IgG4 from CP could not bind granulocytes and presented no suppressive capacity. Reduction of both the affinity to, and the suppressive properties of anti-inflammatory IgG4 on granulocytes was reached only when FcγRI and II were blocked simultaneously. These data indicate that IgG4 antibodies from Mf+, Mf- and EN, in contrast to those of CP, natively exhibit FcγRI/II-dependent suppressive properties on granulocytes. Our findings suggest that quantitative and qualitative alterations in IgG4 molecules are associated with the different clinical phenotypes in LF endemic regions.

Helminth-induced apoptosis: a silent strategy for immunosuppression

During microbial infections, both innate and adaptive immunity are activated. Viruses and bacteria usually induce an acute inflammation in the first setting of infection, which helps the eliciting an effective immune response. In contrast, macroparasites such as helminths are a highly successful group of invaders known to be capable of maintaining a chronic infestation with the minimum instigation. Undoubtedly, generating such an immunoregulatory environment requires the exploitation of various immunosuppressive mechanisms to debilitate host immunity supporting their survival and replication. Several mechanisms have been recognized whereby helminths prolong their infections including an increase of immunoregulatory cells, inhibition of Th1 or Th2 responses, targeting pattern recognition receptors (PRRs) and lowering the immune cells quantity via induction of apoptosis. Apoptosis is a programmed intracellular process involving a series of consecutive downstream signalling event evolved to cell death. It plays a pivotal role in several immunological reactions in particular deletion of autoreactive immune cells. Helminth-triggered apoptosis in immune cells exhausts host immunity, which paves the way for generating a permissive environment and chronic infection. This review provides a compilation of recent investigations discussing the apoptotic mechanisms exploited by different worms and the immunological consequences of immune cell death. Finally, the anti-cancer effects of some worm-derived molecules due to their apoptotic effects are discussed, highlighting as potentially druggable candidates to combat cancer.

Non-Classical monocytes display inflammatory features: Validation in Sepsis and Systemic Lupus Erythematous

Given the importance of monocytes in pathogenesis of infectious and other inflammatory disorders, delineating functional and phenotypic characterization of monocyte subsets has emerged as a critical requirement. Although human monocytes have been subdivided into three different populations based on surface expression of CD14 and CD16, published reports suffer from contradictions with respect to subset phenotypes and function. This has been attributed to discrepancies in reliable gating strategies for flow cytometric characterization and purification protocols contributing to significant changes in receptor expression. By using a combination of multicolour flow cytometry and a high-dimensional automated clustering algorithm to confirm robustness of gating strategy and analysis of ex-vivo activation of whole blood with LPS we demonstrate the following: a. ‘Classical’ monocytes are phagocytic with no inflammatory attributes, b. ‘Non-classical’ subtype display ‘inflammatory’ characteristics on activation and display properties for antigen presentation and c. ‘Intermediate’ subtype that constitutes a very small percentage in circulation (under physiological conditions) appear to be transitional monocytes that display both phagocytic and inflammatory function. Analysis of blood from patients with Sepsis, a pathogen driven acute inflammatory disease and Systemic Lupus Erythmatosus (SLE), a chronic inflammatory disorder validated the broad conclusions drawn in the study.

Autophagy protects monocytes from Wolbachia heat shock protein 60-induced apoptosis and senescence

Monocyte dysfunction by filarial antigens has been a major mechanism underlying immune evasion following hyporesponsiveness during patent lymphatic filariasis. Recent studies have initiated a paradigm shift to comprehend the immunological interactions of Wolbachia and its antigens in inflammation, apoptosis, lymphocyte anergy, etc. Here we showed that recombinant Wolbachia heat shock protein 60 (rWmhsp60) interacts with TLR-4 and induces apoptosis in monocytes of endemic normal but not in chronic patients. Higher levels of reactive oxygen species (ROS) induced after TLR-4 stimulation resulted in loss of mitochondrial membrane potential and caspase cascade activation, which are the plausible reason for apoptosis. Furthermore, release in ROS owing to TLR-4 signaling resulted in the activation of NF-κB p65 nuclear translocation which leads to inflammation and apoptosis via TNF receptor pathway following the increase in IL-6 and TNF-α level. Here for the first time, we report that in addition to apoptosis, rWmhsp60 antigen in filarial pathogenesis also induces molecular senescence in monocytes. Targeting TLR-4, therefore, presents a promising candidate for treating rWmhsp60-induced apoptosis and senescence. Strikingly, induction of autophagy by rapamycin detains TLR-4 in late endosomes and subverts TLR-4-rWmhsp60 interaction, thus protecting TLR-4–mediated apoptosis and senescence. Furthermore, rapamycin-induced monocytes were unresponsive to rWmhsp60, and activated lymphocytes following PHA stimulation. This study demonstrates that autophagy mediates the degradation of TLR-4 signaling and protects monocytes from rWmhsp60 induced apoptosis and senescence.

Despite knowing the significance of Wolbachia in helminth infections, our understanding of immunity and pathogenesis remains incomplete. Therefore, considering the gravity of the problem, the present study provides evidence that Wolbachia heat shock protein 60 induces apoptosis and senescence through TLR-4. Also, binding of rWmhsp60 to TLR-4 triggered caspase cascade activation following, ROS-mediated mitochondrial potential loss. Moreover, we found that nuclear translocation of NF-κB p65 was predominantly related to TLR-4 expression and resulted in apoptosis- and senescence-mediated inflammation via TNF-α and IL-6. Hence, we hypothesized that modifying TLR-4 expression may provide a plausible target for designing antiparasitic drugs. Here we have shown that induction of autophagy by rapamycin destabilizes TLR-4 expression and protects monocytes from rWmhsp60-induced apoptosis and senescence. In addition, rapamycin-induced monocytes were unresponsive to rWmhsp60 and triggered lymphocyte activation after PHA stimulation. Thus, synergistic usage of rapamycin with existing anti-filarial drugs might reduce the TLR-mediated inflammatory reactions following microfilaricidal treatment.