Chronic infection with a tissue-invasive helminth attenuates sublethal anaphylaxis and reduces granularity and number of mast cells.

BACKGROUND: Immunoglobulin E (IgE)-mediated anaphylaxis is a potentially fatal condition in which allergy effector cells rapidly discharge pre-formed inflammatory mediators. Treatments that address the immune component of allergic anaphylaxis are inadequate. Helminths have been previously shown to suppress effector cell function; however, their ability to treat pre-existing allergy remains unclear. OBJECTIVE: To evaluate the ability of chronic helminth infection to protect against anaphylaxis in previously sensitized mice. METHODS: A sublethal model of anaphylaxis was used, in which BALB/c mice were sensitized by three intraperitoneal (i.p.) injections of OVA/alum. Temperature drop was then monitored after systemic OVA challenge in uninfected mice and in mice infected chronically with Litomosoides sigmodontis, a tissue-invasive filarial nematode. RESULTS: Litomosoides sigmodontis-infected mice exhibited significantly lower serum levels of mMCP-1 and were less hypothermic at 30-minute post-challenge compared to uninfected OVA-challenged controls. Characterization of anaphylaxis revealed that FcԑR1 and mast cells were required for hypothermia and elevated serum mMCP-1. OVA-IgE and OVA-IgG1 serum levels were not significantly altered by L sigmodontis infection, and experiments with IL-10-/- mice demonstrated that IL-10 was not required for protection against anaphylaxis. However, peritoneal mast cell numbers were significantly lower in infected mice, and those that were present exhibited decreased granularity by flow cytometry and marked depletion of intracytoplasmic granules by light microscopy. Mast cells from infected mice had lower expression of the activation markers CD200R and CD63 and contained significantly lower basal stores of histamine. CONCLUSIONS: Chronic L sigmodontis infection protects against anaphylaxis, likely due to reduction in mast cell numbers and depletion of pre-formed inflammatory mediators in remaining mast cells.

The immune response of inbred laboratory mice to Litomosoides sigmodontis: A route to discovery in myeloid cell biology.

Litomosoides sigmodontis is the only filarial nematode where the full life cycle, from larval delivery to the skin through to circulating microfilaria, can be completed in immunocompetent laboratory mice. It is thus an invaluable tool for the study of filariasis. It has been used for the study of novel anti-helminthic therapeutics, the development of vaccines against filariasis, the development of immunomodulatory drugs for the treatment of inflammatory disease and the study of basic immune responses to filarial nematodes. This review will focus on the latter and aims to summarize how the L sigmodontis model has advanced our basic understanding of immune responses to helminths, led to major discoveries in macrophage biology and provided new insights into the immunological functions of the pleural cavity. Finally, and most importantly L sigmodontis represents a suitable platform to study how host genotype affects immune responses, with the potential for further discovery in myeloid cell biology and beyond.

The central adaptor molecule TRIF influences L. sigmodontis worm development.

Worldwide approximately 68 million people are infected with lymphatic filariasis (Lf), provoked by Wuchereria bancrofti, Brugia malayi and Brugia timori. This disease can lead to massive swelling of the limbs (elephantiasis) and disfigurement of the male genitalia (hydrocele). Filarial induced immune regulation is characterised by dominant type 2 helper T cell and regulatory immune responses. In vitro studies have provided evidence that signalling via Toll-like receptor-mediated pathways is triggered by filarial associated factors. Nevertheless, until now, less is known about the role of the adapter molecule TRIF during in vivo infections. Here, we used the rodent-specific nematode Litomosoides sigmodontis to investigate the role of TLR signalling and the corresponding downstream adapter and regulatory molecules TRIF, MyD88, IRF1 and IRF3 during an ongoing infection in semi-susceptible C57BL/6 mice. Interestingly, lack of the central adapter molecule TRIF led to higher worm burden and reduced overall absolute cell numbers in the thoracic cavity (the site of infection) 30 days post-infection. In addition, frequencies of macrophages and lymphocytes in the TC were increased in infected TRIF-/- C57BL/6 mice, whereas frequencies of eosinophils, CD4+ and CD8+ T cells were reduced. Nevertheless, cytokine levels and regulatory T cell populations remained comparable between TRIF-deficient and wildtype C57BL/6 mice upon 30 days of L. sigmodontis infection. In summary, this study revealed a crucial role of the adapter molecule TRIF on worm recovery and immune cell recruitment into the site of infection 30 days upon L. sigmodontis infection in C57BL/6 mice.

Species-specific and cross-reactive antigen of filarial worm: Brugia malayi and Setaria digitata.

BACKGROUND & OBJECTIVES: Generally filarial antigens have been found to be cross-reactive in nature. Identification of genus and species-specific antigens has not been successful so far. Due to lack of human adult filarial parasite, researchers have been using other adult worms like Setaria digitata, a cattle parasite or Brugia malayi, a rodent model for their research work. In this situation, specificity of the prepared antigen (S. digitata or B. malayi) to detect the antibodies to Wuchereria bancrofti is questionable. METHODS: In the present investigation, we have tested a panel of human sera (collected from the areas, endemic for bancroftian filariasis) to correlate the immune reactivity against somatic antigens of adult stages and microfilarial stages of S. digitata and B. malayi. Further, using intact microfilariae (mf) from the above two parasites along with W. bancrofti, we have analyzed the antibody response to the sheath antigens. A panel of infected human and cattle sera was tested by immunoperoxidase assay using intact mf of three different parasites, viz. W. bancrofti, B. malayi, and S. digitata. RESULTS: A very significant positive correlation in filarial Igs (polyvalent), IgG, IgM, IgE and IgG4 levels were found between the two adult somatic antigens of B. malayi and S. digitata when tested against human filarial sera. However, such a correlation was not found when mf antigens of B. malayi and S. digitata were tested against a panel of W. bancrofti sera indicating that antigens present in mf could be far less cross-reactive in comparison to those in adult stage parasites. INTERPRETATION & CONCLUSION: The results indicated the differential cross-reactivity of antisheath antibodies to the mf sheath of three different filarial parasites. Soluble antigens of S. digitata could inhibit antisheath antibody reactivity to only S. digitata mf sheath and not to mf sheath of W. bancrofti further confirming the specificity of sheath antigen.

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.

Absence of IL-17A in Litomosoides sigmodontis-infected mice influences worm development and drives elevated filarial-specific IFN-γ.

Lymphatic filariasis, onchocerciasis and loiasis are widespread neglected tropical diseases causing serious public health problems and impacting the socio-economic climate in endemic communities. More than 100 million people currently suffer from filarial infections but disease-related symptoms and infection-induced immune mechanisms are still ambiguous. Although most infected individuals have dominant Th2 and regulatory immune responses leading to a homeostatic regulated state, filarial-induced overt pathology like lymphedema, dermal pathologies or blindness can occur. Interestingly, besides dominant Th2 and regulatory T cell activation, increased Th17-induced immune responses were associated with filarial infection and overt helminth-induced pathology in humans. However, the immunological mechanisms of Th17 cells and the release of IL-17A during filarial infections remain unclear. To decipher the role of IL-17A during filarial infection, we naturally infected IL-17A-/- and wildtype C57BL/6 mice with the rodent filariae Litomosoides sigmodontis and analysed parasite development and immune alterations. Our study reveals that infected IL-17A-deficient C57BL/6 mice present reduced worm burden on days 7 and 28 p.i. but had longer adult worms on day 28 p.i. in the thoracic cavity (TC), the site of infection. In addition, infiltration of CD4+ T cells, CD4+Foxp3+ regulatory T and functional CD4+Rorγt+pStat3+ Th17 cells in the TC was reduced in IL-17A-deficient mice accompanied by reduced eotaxin-1 and CCL17 levels. Furthermore, mediastinal lymph node cells isolated from IL-17A-/- mice showed increased filarial-specific IFN-γ but not IL-4, IL-6, or IL-21 secretion. This study shows that Th17 signalling is important for host immune responses against filarial infection but appears to facilitate worm growth in those that reach the TC.

IL-33 delivery induces serous cavity macrophage proliferation independent of interleukin-4 receptor alpha.

IL-33 plays an important role in the initiation of type-2 immune responses, as well as the enhancement of type 2 effector functions. Engagement of the IL-33 receptor on macrophages facilitates polarization to an alternative activation state by amplifying IL-4 and IL-13 signaling to IL-4Rα. IL-4 and IL-13 also induce macrophage proliferation but IL-33 involvement in this process has not been rigorously evaluated. As expected, in vivo delivery of IL-33 induced IL-4Rα-dependent alternative macrophage activation in the serous cavities. IL-33 delivery also induced macrophages to proliferate but, unexpectedly, this was independent of IL-4Rα signaling. In a filarial nematode infection model in which IL-4Rα-dependent alternative activation and proliferation in the pleural cavity is well described, IL-33R was essential for alternative activation but not macrophage proliferation. Similarly, during Alternaria alternata induced airway inflammation, which provokes strong IL-33 responses, we observed that both IL-4Rα and IL-33R were required for alternative activation, while macrophage proliferation in the pleural cavity was still evident in the absence of either receptor alone. Our data show that IL-33R and IL-4Rα promote macrophage proliferation independently of each other, but both are essential for induction of alternative activation.

Chronic filarial infection provides protection against bacterial sepsis by functionally reprogramming macrophages.

Helminths immunomodulate their hosts and induce a regulatory, anti-inflammatory milieu that prevents allergies and autoimmune diseases. Helminth immunomodulation may benefit sepsis outcome by preventing exacerbated inflammation and severe pathology, but the influence on bacterial clearance remains unclear. To address this, mice were chronically infected with the filarial nematode Litomosoides sigmodontis (L.s.) and the outcome of acute systemic inflammation caused by i.p. Escherichia coli injection was determined. L.s. infection significantly improved E. coli-induced hypothermia, bacterial clearance and sepsis survival and correlated with reduced concentrations of associated pro-inflammatory cytokines/chemokines and a less pronounced pro-inflammatory macrophage gene expression profile. Improved sepsis outcome in L.s.-infected animals was mediated by macrophages, but independent of the alternatively activated macrophage subset. Endosymbiotic Wolbachia bacteria that are present in most human pathogenic filariae, as well as L.s., signal via TLR2 and modulate macrophage function. Here, gene expression profiles of peritoneal macrophages from L.s.-infected mice revealed a downregulation of genes involved in TLR signaling, and pulsing of macrophages in vitro with L.s. extract reduced LPS-triggered activation. Subsequent transfer improved sepsis outcome in naïve mice in a Wolbachia- and TLR2-dependent manner. In vivo, phagocytosis was increased in macrophages from L.s.-infected wild type, but not TLR2-deficient animals. In association, L.s. infection neither improved bacterial clearance in TLR2-deficient animals nor ameliorated E. coli-induced hypothermia and sepsis survival. These results indicate that chronic L.s. infection has a dual beneficial effect on bacterial sepsis, reducing pro-inflammatory immune responses and improving bacterial control. Thus, helminths and their antigens may not only improve the outcome of autoimmune and allergic diseases, but may also present new therapeutic approaches for acute inflammatory diseases that do not impair bacterial control.

Immunity in Filarial Infections: Lessons from Animal Models and Human Studies.

Our understanding of immunity to filarial infection is enigmatic and continues to be passionately debated. The mechanisms whereby filarial nematodes are killed in vivo and how these parasites avoid these mechanisms are poorly understood. Although vaccination studies in permissive animals took off seven decades ago, the exact mechanisms driving protective immunity are extensively being investigated. Currently, little is known regarding the collective functions or counter-regulatory mechanisms of the antibody isotypes in filarial infection with respect to protective immunity. Establishing the functional role of antibody isotypes and cytokines in the various infection phenotypes can contribute immensely to current knowledge in filarial immunology. This paper reviews insight into protective immunity in filarial infection with focus on humoral and cellular responses from animal models and human studies.

Ten Weeks of Infection with a Tissue-Invasive Helminth Protects against Local Immune Complex-Mediated Inflammation, but Not Cutaneous Type I Hypersensitivity, in Previously Sensitized Mice.

In this study, we evaluated the effect chronic helminth infection has on allergic disease in mice previously sensitized to OVA. Ten weeks of infection with Litomosoides sigmodontis reduced immunological markers of type I hypersensitivity, including OVA-specific IgE, basophil activation, and mast cell degranulation. Despite these reductions, there was no protection against immediate clinical hypersensitivity following intradermal OVA challenge. However, late-phase ear swelling, due to type III hypersensitivity, was significantly reduced in chronically infected animals. Levels of total IgG2a, OVA-specific IgG2a, and OVA-specific IgG1 were reduced in the setting of infection. These reductions were most likely due to increased Ab catabolism as ELISPOT assays demonstrated that infected animals do not have suppressed Ab production. Ear histology 24 h after challenge showed infected animals have reduced cellular infiltration in the ear, with significant decreases in numbers of neutrophils and macrophages. Consistent with this, infected animals had less neutrophil-specific chemokines CXCL-1 and CXCL-2 in the ear following challenge. Additionally, in vitro stimulation with immune complexes resulted in significantly less CXCL-1 and CXCL-2 production by eosinophils from chronically infected mice. Expression of FcγRI was also significantly reduced on eosinophils from infected animals. These data indicate that chronic filarial infection suppresses eosinophilic responses to Ab-mediated activation and has the potential to be used as a therapeutic for pre-existing hypersensitivity diseases.

Patency of Litomosoides sigmodontis infection depends on Toll-like receptor 4 whereas Toll-like receptor 2 signalling influences filarial-specific CD4(+) T-cell responses.

BALB/c mice develop a patent state [release of microfilariae (Mf), the transmission life-stage, into the periphery] when exposed to the rodent filariae Litomosoides sigmodontis. Interestingly, only a portion of the infected mice become patent, which reflects the situation in human individuals infected with Wuchereria bancrofti. Since those individuals had differing filarial-specific profiles, this study compared differences in immune responses between Mf(+) and Mf(-) infected BALB/c mice. We demonstrate that cultures of total spleen or mediastinal lymph node cells from Mf(+) mice produce significantly more interleukin-5 (IL-5) to filarial antigens but equal levels of IL-10 when compared with Mf(-) mice. However, isolated CD4(+) T cells from Mf(+) mice produced significantly higher amounts of all measured cytokines, including IL-10, when compared with CD4(+) T-cell responses from Mf(-) mice. Since adaptive immune responses are influenced by triggering the innate immune system we further studied the immune profiles and parasitology in infected Toll-like receptor-2-deficient (TLR2(-/-)) and TLR4(-/-) BALB/c mice. Ninety-three per cent of L. sigmodontis-exposed TLR4(-/-) BALB/c mice became patent (Mf(+)) although worm numbers remained comparable to those in Mf(+) wild-type controls. Lack of TLR2 had no influence on patency outcome or worm burden but infected Mf(+) mice had significantly lower numbers of Foxp3(+) regulatory T cells and dampened peripheral immune responses. Interestingly, in vitro culturing of CD4(+) T cells from infected wild-type mice with granulocyte-macrophage colony-stimulating factor-derived TLR2(-/-) dendritic cells resulted in an overall diminished cytokine profile to filarial antigens. Hence, triggering TLR4 or TLR2 during chronic filarial infection has a significant impact on patency and efficient CD4(+) T-cell responses, respectively.

Combination of worm antigen and proinsulin prevents type 1 diabetes in NOD mice after the onset of insulitis.

Animal studies demonstrated that administration of helminth products can protect from autoimmune diseases. However, the success of such administrations is limited in the case of type 1 diabetes, as protection is only provided if the administration is started before the development of insulitis. In this study we investigated whether inclusion of helminth antigen administrations to an antigen-specific treatment with proinsulin improves the protective effect by triggering non-specific regulatory immune responses. Using a combination therapy of intraperitoneal Litomosoides sigmodontis antigen and intranasal pro-insulin, onset of diabetes was prevented in NOD mice after insulitis started, while either administration alone failed to protect. This protection was associated with an increased frequency of regulatory T cells within the pancreatic lymph nodes and a reduced inflammation of the pancreatic islets. This suggests that inclusion of helminth antigens improve the protective effect provided by antigen-specific therapies and represent a new potential therapeutic approach against autoimmune diseases.

Litomosoides sigmodontis induces TGF-ß receptor responsive, IL-10-producing T cells that suppress bystander T-cell proliferation in mice.

Helminth parasites suppress immune responses to prolong their survival within the mammalian host. Thereby not only helminth-specific but also nonhelminth-specific bystander immune responses are suppressed. Here, we use the murine model of Litomosoides sigmodontis infection to elucidate the underlying mechanisms leading to this bystander T-cell suppression. When OT-II T cells specific for the third-party antigen ovalbumin are transferred into helminth-infected mice, these cells respond to antigen-specific stimulation with reduced proliferation compared to activation within non-infected mice. Thus, the presence of parasitic worms in the thoracic cavity translates to suppression of T cells with a different specificity at a different site. By eliminating regulatory receptors, cytokines, and cell populations from this system, we provide evidence for a two-staged process. Parasite products first engage the TGF-ß receptor on host-derived T cells that are central to suppression. In a second step, host-derived T cells produce IL-10 and subsequently suppress the adoptively transferred OT-II T cells. Terminal suppression was IL-10-dependant but independent of intrinsic TGF-ß receptor- or PD-1-mediated signaling in the suppressed OT-II T cells. Blockade of the same key suppression mediators, i.e. TGF-ß- and IL-10 receptor, also ameliorated the suppression of IgG response to bystander antigen vaccination in L. sigmodontis-infected mice.

Escherichia coli-induced immune paralysis is not exacerbated during chronic filarial infection.

Sepsis initially starts with a systemic inflammatory response (SIRS phase) and is followed by a compensatory anti-inflammatory response syndrome (CARS) that causes impaired adaptive T-cell immunity, immune paralysis and an increased susceptibility to secondary infections. In contrast, parasitic filariae release thousands of microfilariae into the peripheral blood without triggering inflammation, as they induce regulatory, anti-inflammatory host responses. Hence, we investigated the impact of chronic filarial infection on adaptive T-cell responses during the SIRS and CARS phases of a systemic bacterial infection and analysed the development of T-cell paralysis following a subsequent adenovirus challenge in BALB/c mice. Chronic filarial infection impaired adenovirus-specific CD8(+) T-cell cytotoxicity and interferon-γ responses in the absence of a bacterial challenge and led to higher numbers of splenic CTLA-4(+)  CD4(+) T cells, whereas splenic T-cell expression of CD69 and CD62 ligand, serum cytokine levels and regulatory T-cell frequencies were comparable to naive controls. Irrespective of filarial infection, the SIRS phase dominated 6-24 hr after intravenous Escherichia coli challenge with increased T-cell activation and pro-inflammatory cytokine production, whereas the CARS phase occurred 6 days post E. coli challenge and correlated with high levels of transforming growth factor-ß and increased CD62 ligand T-cell expression. Escherichia coli-induced impairment of adenovirus-specific CD8(+) T-cell cytotoxicity and interferon-γ production was not additionally impaired by chronic filarial infection. This suggests that filarial immunoregulation does not exacerbate E. coli-induced T-cell paralysis.

Th2 cell-intrinsic hypo-responsiveness determines susceptibility to helminth infection.

The suppression of protective Type 2 immunity is a principal factor driving the chronicity of helminth infections, and has been attributed to a range of Th2 cell-extrinsic immune-regulators. However, the intrinsic fate of parasite-specific Th2 cells within a chronic immune down-regulatory environment, and the resultant impact such fate changes may have on host resistance is unknown. We used IL-4gfp reporter mice to demonstrate that during chronic helminth infection with the filarial nematode Litomosoides sigmodontis, CD4(+) Th2 cells are conditioned towards an intrinsically hypo-responsive phenotype, characterised by a loss of functional ability to proliferate and produce the cytokines IL-4, IL-5 and IL-2. Th2 cell hypo-responsiveness was a key element determining susceptibility to L. sigmodontis infection, and could be reversed in vivo by blockade of PD-1 resulting in long-term recovery of Th2 cell functional quality and enhanced resistance. Contrasting with T cell dysfunction in Type 1 settings, the control of Th2 cell hypo-responsiveness by PD-1 was mediated through PD-L2, and not PD-L1. Thus, intrinsic changes in Th2 cell quality leading to a functionally hypo-responsive phenotype play a key role in determining susceptibility to filarial infection, and the therapeutic manipulation of Th2 cell-intrinsic quality provides a potential avenue for promoting resistance to helminths.

Pleural cavity type 2 innate lymphoid cells precede Th2 expansion in murine Litomosoides sigmodontis infection.

Recently, a family of innate cells has been identified that respond to IL-25 and IL-33 in murine intestinal helminths. Termed Type 2 innate lymphoid cells (ILC2s) they facilitate the development of Th2 responses responsible for helminth clearance. We evaluated these cells in a tissue-invasive helminth model. Using Litomosides sigmodontis (a strong Th2 polarizing filarial infection) we observed a robust Th2 response in the pleural cavity, where adult worms reside, marked by increased levels of IL-5 and IL-13 in infected mice. In parallel, ILC2s were expanded in the pleural cavity early in the infection, peaking during the pre-patent period. L. sigmodontis also elicits a strong systemic Th2 response, which includes significantly increased levels of IgG1, IgE and IL-5 in the plasma of infected mice. Although ILC2s were expanded locally, they were not expanded in the spleen, blood, or mediastinal lymph nodes in response to L. sigmodontis infection, suggesting that ILC2s function primarily at the site of infection. The increase in ILC2s in the pleural cavity and the expansion in Th2 responses indicates a probable role for these cells in initiating and maintaining the Th2 response and highlights the importance of these cells in helminth infections and their role in Th2 immunity.

A comprehensive, model-based review of vaccine and repeat infection trials for filariasis.

SUMMARY Filarial worms cause highly morbid diseases such as elephantiasis and river blindness. Since the 1940s, researchers have conducted vaccine trials in 27 different animal models of filariasis. Although no vaccine trial in a permissive model of filariasis has provided sterilizing immunity, great strides have been made toward developing vaccines that could block transmission, decrease pathological sequelae, or decrease susceptibility to infection. In this review, we have organized, to the best of our ability, all published filaria vaccine trials and reviewed them in the context of the animal models used. Additionally, we provide information on the life cycle, disease phenotype, concomitant immunity, and natural immunity during primary and secondary infections for 24 different filaria models.

T-cell-derived, but not B-cell-derived, IL-10 suppresses antigen-specific T-cell responses in Litomosoides sigmodontis-infected mice.

IL-10, a cytokine with pleiotropic functions is produced by many different cells. Although IL-10 may be crucial for initiating protective Th2 responses to helminth infection, it may also function as a suppressive cytokine preventing immune pathology or even contributing to helminth-induced immune evasion. Here, we show that B cells and T cells produce IL-10 during murine Litomosoides sigmodontis infection. IL-10-deficient mice produced increased amounts of L. sigmodontis-specific IFN-γ and IL-13 suggesting a suppressive role for IL-10 in the initiation of the T-cell response to infection. Using cell type-specific IL-10-deficient mice, we dissected different functions of T-cell- and B-cell-derived IL-10. Litomosoides sigmodontis-specific IFN-γ, IL-5, and IL-13 production increased in the absence of T-cell-derived IL-10 at early and late time points of infection. In contrast, B-cell-specific IL-10 deficiency did not lead to significant changes in L. sigmodontis-specific cytokine production compared to WT mice. Our results suggest that the initiation of Ag-specific cellular responses during L. sigmodontis infection is suppressed by T-cell-derived IL-10 and not by B-cell-derived IL-10.

Immunization with Brugia malayi Hsp70 protects mice against Litomosoides sigmodontis challenge infection.

More than 1·5 billion people are at risk of being infected with filarial nematodes worldwide. Therapy and control of transmission are mainly based on mass drug distribution. As these drugs have to be administered annually or biannually and might be loosing their efficacy, a vaccine against filariae is an alternative approach to chemotherapy. In the current study, we have analysed the potential of Brugia malayi heat shock protein 70 (BmHsp70) as a vaccine candidate in a murine helminth infection. Immunization of BALB/c mice with alum-precipitated recombinant BmHsp70 conferred partial protection against subsequent challenge infection with the rodent parasite Litomosoides sigmodontis. Immunization resulted in reduced numbers of larvae in the pleural cavity as well as reduced numbers of circulating microfilariae. Reduced parasite burden was associated with high titres of BmHsp70-specific antibodies and increased production of type I and II cytokines in response to L. sigmodontis antigen and BmHsp70. In summary, the immunization with BmHsp70 induced cellular and humoral immune responses and partially protected against L. sigmodontis in a challenge infection. Therefore, we hypothesize that BmHsp70 might be considered as a potential vaccine candidate for reduction in the incidence of B. malayi infections in future studies.

Eotaxin-1 is involved in parasite clearance during chronic filarial infection.

Eosinophil migration as key feature of helminth infection is increased during infection with filarial nematodes. In a mouse model of filariasis, we investigated the role of the eosinophil-attracting chemokine Eotaxin-1 on disease outcome. BALB/c and Eotaxin-1(-/-) mice were infected with the rodent filaria Litomosoides sigmodontis, and parasitic parameters, cellular migration to the site of infection, and cellular responsiveness were investigated. We found increased parasite survival but unaffected eosinophil migration to the site of infection in Eotaxin-1(-/-) mice. Expression of CD80 and CD86 was reduced on eosinophils from Eotaxin-1(-/-) mice after in vitro TLR2 stimulation and exposure to filarial antigen, respectively, suggesting a potential reduced activation state of eosinophils in Eotaxin-1 deficient mice. We further demonstrated that macrophages from Eotaxin-1(-/-) mice produce decreased amounts of IL-6 in vitro, a cytokine found to be associated with parasite containment, suggesting possible mechanisms by which Eotaxin-1 regulates activation of inflammatory cells and thus parasite survival.