Filarial infection induces protection against P. berghei liver stages in mice

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.

Spleen nodules in Loa loa infection: re-emerging knowledge and future perspectives

Loiasis, the infection with the vector-borne filarial nematode Loa loa, is widely distributed in central and west Africa. Long considered a rather benign infection, recently loiasis with high microfilarial burden was associated with increased mortality risk. Eyeworm and Calabar swelling are pathognomonic signs of the infection, but other atypical, non-specific manifestations can also occur. For instance, splenic nodules have been seldom reported. In this Grand Round, we report two cases of loiasis in migrants who presented with spleen nodules, which could be followed up over time (up to 27 months) with multiple imaging techniques until their resolution. We comment on the clinical implications of these observations, including differential diagnosis with similar imaging findings, and critically review the evidence of spleen involvement in loiasis and other filarial infections.

Concurrent Infection With the Filarial Helminth Litomosoides sigmodontis Attenuates or Worsens Influenza A Virus Pathogenesis in a Stage-Dependent Manner

Filarial helminths infect approximately 120 million people worldwide initiating a type 2 immune response in the host. Influenza A viruses stimulate a virulent type 1 pro-inflammatory immune response that in some individuals can cause uncontrolled immunopathology and fatality. Although coinfection with filariasis and influenza is a common occurrence, the impact of filarial infection on respiratory viral infection is unknown. The aim of this study was to determine the impact of pre-existing filarial infection on concurrent infection with influenza A virus. A murine model of co-infection was established using the filarial helminth Litomosoides sigmodontis and the H1N1 (A/WSN/33) influenza A virus (IAV). Co-infection was performed at 3 different stages of L. sigmodontis infection (larval, juvenile adult, and patency), and the impact of co-infection was determined by IAV induced weight loss and clinical signs, quantification of viral titres, and helminth counts. Significant alterations of IAV pathogenesis, dependent upon stage of infection, was observed on co-infection with L. sigmodontis. Larval stage L. sigmodontis infection alleviated clinical signs of IAV co-infection, whilst more established juvenile adult infection also significantly delayed weight loss. Viral titres remained unaltered at either infection stage. In contrast, patent L. sigmdodontis infection led to a reversal of age-related resistance to IAV infection, significantly increasing weight loss and clinical signs of infection as well as increasing IAV titre. These data demonstrate that the progression of influenza infection can be ameliorated or worsened by pre-existing filarial infection, with the outcome dependent upon the stage of filarial infection.

Effect of Brugia pahangi co-infection with Plasmodium berghei ANKA in gerbils (Meriones unguiculatus)

Malaria and lymphatic filariasis (LF) are two leading and common mosquito-borne parasitic diseases worldwide. These two diseases are co-endemic in many tropical and sub-tropical regions and are known to share vectors. The interactions between malaria and filarial parasites are poorly understood. Thus, this study aimed at establishing the interactions that occur between Brugia pahangi and Plasmodium berghei ANKA (PbA) co-infection in gerbils. Briefly, the gerbils were matched according to age, sex, and weight and grouped into filarial-only infection, PbA-only infection, co-infection, and control group. The parasitemia, survival and clinical assessment of the gerbils were monitored for a period of 30 days post Plasmodium infection. The immune responses of gerbils to both mono and co-infection were monitored. Findings show that co-infected gerbils have higher survival rate than PbA-infected gerbils. Food and water consumption were significantly reduced in both PbA-infected and co-infected gerbils, although loss of body weight, hypothermia, and anemia were less severe in co-infected gerbils. Plasmodium-infected gerbils also suffered hypoglycemia, which was not observed in co-infected gerbils. Furthermore, gerbil cytokine responses to co-infection were significantly higher than PbA-only-infected gerbils, which is being suggested as a factor for their increased longevity. Co-infected gerbils had significantly elicited interleukin-4, interferon-gamma, and tumor necrotic factor at early stage of infection than PbA-infected gerbils. Findings from this study suggest that B. pahangi infection protect against severe anemia and hypoglycemia, which are manifestations of PbA infection.

Infection against infection: parasite antagonism against parasites, viruses and bacteria

Background

Infectious diseases encompass a large spectrum of diseases that threaten human health, and coinfection is of particular importance because pathogen species can interact within the host. Currently, the antagonistic relationship between different pathogens during concurrent coinfections is defined as one in which one pathogen either manages to inhibit the invasion, development and reproduction of the other pathogen or biologically modulates the vector density. In this review, we provide an overview of the phenomenon and mechanisms of antagonism of coinfecting pathogens involving parasites.

Main body

This review summarizes the antagonistic interaction between parasites and parasites, parasites and viruses, and parasites and bacteria. At present, relatively clear mechanisms explaining polyparasitism include apparent competition, exploitation competition, interference competition, biological control of intermediate hosts or vectors and suppressive effect on transmission. In particular, immunomodulation, including the suppression of dendritic cell (DC) responses, activation of basophils and mononuclear macrophages and adjuvant effects of the complement system, is described in detail.

Conclusions

In this review, we summarize antagonistic concurrent infections involving parasites and provide a functional framework for in-depth studies of the underlying mechanisms of coinfection with different microorganisms, which will hasten the development of promising antimicrobial alternatives, such as novel antibacterial vaccines or biological methods of controlling infectious diseases, thus relieving the overwhelming burden of ever-increasing antimicrobial resistance.

Electronic supplementary material

The online version of this article (10.1186/s40249-019-0560-6) contains supplementary material, which is available to authorized users.

Cross reactive molecules of human lymphatic filaria Brugia malayi inhibit Leishmania donovani infection in hamsters

Coinfections are common in natural populations and the outcome of their interactions depends on the immune responses of the host elicited by the parasites. Earlier we showed that immunization with BmAFII (Sephadex G-200 eluted) fraction of human lymphatic filaria Brugia malayi inhibited progression of Leishmania donovani infection in golden hamsters. In the present study we identified cross reactive molecules of B. malayi, and investigated their effect on L. donovani infection and associated immune responses in the host. The sequence alignment and sharing of linear T- and B-cell epitopes in protein molecules of B. malayi and L. donovani counterparts were studied in silico. Hamsters were immunized with robustly cross reactive SDS-PAGE resolved fractions F6 (54.2-67.8kDa) and F9 (41.3-45.0kDa) of B. malayi and subsequently inoculated with amastigotes of L. donovani intracardially. F6 inhibited (∼72%) L. donovani infection and upregulated Th1 cytokine expression, lymphoproliferation, IgG2, IgG2/3 levels and NO production, and downregulated Th2 cytokine expression. Sequences in HSP60 and EF-2 of F6 and L. donovani counterparts were conserved and B- and T-cell epitopes in the proteins shared antigenic regions. In conclusion, leishmania-cross reactive molecules of filarial parasite considerably inhibited leishmanial infection via Th1-mediated immune responses and NO production. Common B- and T-cell epitope regions in HSP60 and EF-2 of the parasites might have contributed to the inhibitory effect on the L. donovani infection. Thus, leishmania-cross reactive filarial parasite molecules may help in designing prophylactic(s) against L. donovani.

Malaria endemicity and co-infection with tissue-dwelling parasites in Sub-Saharan Africa: a review

Mechanisms and outcomes of host-parasite interactions during malaria co-infections with gastrointestinal helminths are reasonably understood. In contrast, very little is known about such mechanisms in cases of malaria co-infections with tissue-dwelling parasites. This is lack of knowledge is exacerbated by misdiagnosis, lack of pathognomonic clinical signs and the chronic nature of tissue-dwelling helminthic infections. A good understanding of the implications of tissue-dwelling parasitic co-infections with malaria will contribute towards the improvement of the control and management of such co-infections in endemic areas. This review summarises and discusses current information available and gaps in research on malaria co-infection with gastro-intestinal helminths and tissue-dwelling parasites with emphasis on helminthic infections, in terms of the effects of migrating larval stages and intra and extracellular localisations of protozoan parasites and helminths in organs, tissues, and vascular and lymphatic circulations.

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-β 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.

Parasite virulence, co-infections and cytokine balance in malaria

Strong early inflammatory responses followed by a timely production of regulatory cytokines are required to control malaria parasite multiplication without inducing major host pathology. Here, we briefly examine the homeostasis of inflammatory responses to malaria parasite species with varying virulence levels and discuss how co-infections with bacteria, viruses, and helminths can modulate inflammation, either aggravating or alleviating malaria-related morbidity.

Co-infection restrains Litomosoides sigmodontis filarial load and plasmodial P. yoelii but not P. chabaudi parasitaemia in mice

Infection with multiple parasite species is clearly the norm rather than the exception, in animals as well as in humans. Filarial nematodes and Plasmodium spp. are important parasites in human public health and they are often co-endemic. Interactions between these parasites are complex. The mechanisms underlying the modulation of both the course of malaria and the outcome of filarial infection are poorly understood. Despite increasing activity in recent years, studies comparing co- and mono-infections are very much in their infancy and results are contradictory at first sight. In this study we performed controlled and simultaneous co-infections of BALB/c mice with Litomosoides sigmodontis filaria and with Plasmodium spp. (Plasmodium yoelii 17 XNL or Plasmodium chabaudi 864VD). An analysis of pathological lesions in the kidneys and lungs and a parasitological study were conducted at different times of infection. Whatever the plasmodial species, the filarial recovery rate was strongly decreased. The peak of parasitaemia in the plasmodial infection was decreased in the course of P. yoelii infection but not in that of P. chabaudi. Regarding pathological lesions, L. sigmodontis can reverse lesions in the kidneys due to the presence of both Plasmodium species but does not modify the course of pulmonary lesions. The filarial infection induces granulomas in the lungs.

Regulatory T cell subsets in filarial infection and their function

Filarial infections in humans are chronic infections that cause significant morbidity. The chronic nature of these infections with continuous antigen release is associated with a parasite-specific T cell hypo-responsiveness that may over time also affect the immune responses to bystander antigens. Previous studies have shown the filarial parasite antigen-specific T cells hypo-responsiveness is mediated by regulatory cytokines – IL-10 and TGF-β in particular. Recent studies have suggested that the modulated/regulated T cell responses associated with patent filarial infection may reflect an expansion of regulatory T cells (Tregs) that include both Tregs induced in peripheral circulation or pTregs and the thymus-derived Tregs or tTregs. Although much is known about the phenotype of these regulatory populations, the mechanisms underlying their expansion and their mode of action in filarial and other infections remain unclear. Nevertheless there are data to suggest that while many of these regulatory cells are activated in an antigen-specific manner the ensuing effectors of this activation are relatively non-specific and may affect a broad range of immune cells. This review will focus on the subsets and function of regulatory T cells in filarial infection.

Pre-existing Schistosoma japonicum infection alters the immune response to Plasmodium berghei infection in C57BL/6 mice

BACKGROUND

Since helminths and malaria parasites are often co-endemic, it is important to clarify the immunoregulatory mechanism that occurs during the process of co-infection. A previous study confirmed that dendritic cells (DCs) are involved in the establishment and regulation of the T-cell-mediated immune response to malaria infection. In the current study, distinct response profiles for splenic DCs and regulatory T cell (Treg) responses were assessed to evaluate the effects of a pre-existing Schistosoma japonicum infection on malaria infection.

METHODS

Malaria parasitaemia, survival rate, brain histopathology and clinical experimental cerebral malaria (ECM) were assessed in both Plasmodium berghei ANKA-mono-infected and S. japonicum-P. berghei ANKA-co-infected mice. Cell surface/intracellular staining and flow cytometry were used to analyse the level of splenic DC subpopulations, toll-like receptors (TLRs), DC surface molecules, Tregs (CD4⁺CD25⁺Foxp3⁺), IFN-γ/IL-10-secreting Tregs, and IFN-γ⁺/IL-10⁺-Foxp3⁻CD4⁺ T cells. IFN-γ, IL-4, IL-5, IL-10 and IL-13 levels were determined in splenocyte supernatants using enzyme-linked immunosorbent assay (ELISA).

RESULTS

The co-infected mice had significantly higher malaria parasitaemia, compared with the mono-infected mice, on days 2, 3, 7 and 8 after P. berghei ANKA infection. Mono-infected mice had a slightly lower survival rate, while clinical ECM symptoms, and brain pathology, were significantly more severe during the period of susceptibility to ECM. On days 5 and 8 post P. berghei ANKA infection, co-infected mice had significantly lower levels of CD11c⁺CD11b⁺, CD11c⁺CD45R/B220⁺, CD11c⁺TLR4⁺, CD11c⁺TLR9⁺, CD11c⁺MHCII⁺, CD11c⁺CD86⁺, IFN-γ-secreting Tregs, and IFN-γ⁺Foxp3⁻CD4⁺ T cells in single-cell suspensions of splenocytes when compared with P. berghei ANKA-mono-infected mice. Co-infected mice also had significantly lower levels of IFN-γ and higher levels of IL-4, IL-5, and IL-13 in splenocyte supernatants compared to mono-infected mice. There were no differences in the levels of IL-10-secreting Tregs or IL-10⁺Foxp3⁻CD4⁺ T cells between co-infected and mono-infected mice.

CONCLUSIONS

A Tregs-associated Th2 response plays an important role in protecting against ECM pathology. Pre-existing S. japonicum infection suppressed TLR ligand-induced DC maturation and had an anti-inflammatory effect during malaria infection not only by virtue of its ability to induce Th2 responses, but also by directly suppressing the ability of DC to produce pro-inflammatory mediators.

Impact of filarial infections on coincident intracellular pathogens: Mycobacterium tuberculosis and Plasmodium falciparum

PURPOSE OF REVIEW

To examine the consequences of the immune modulation seen in chronic filarial infection on responses to intracellular pathogens (and their antigens) that are often co-endemic with filarial infections, namely Plasmodium and Mycobacterium tuberculosis.

RECENT FINDINGS

Much of the recent data on filaria/mycobacteria or filaria/Plasmodium co-infection has focused on the modulation of mycobacteria-specific or malaria-specific responses by chronic filarial infection. As such, filarial infections very clearly alter the magnitude and quality of the mycobacteria-specific or malaria-specific cytokine responses, responses that have been typically associated with control of these intracellular pathogens.

SUMMARY

Although phylogenetically distinct, mycobacteria and Plasmodium spp. often share the same geographical niche with filarial infections. The complex interplay between filarial parasites that are associated with immunomodulation and those microbial pathogens that require a proinflammatory or unmodulated response for their control is easily demonstrable ex vivo, but whether this interplay affects disease outcome in tuberculosis or malaria remains an open question.

Interactions between worms and malaria: good worms or bad worms?

In the past decade there have been an increasing number of studies on co-infections between worms and malaria. However, this increased interest has yielded results that have been at times conflicting and made it difficult to clearly grasp the outcome of this interaction. Despite the heterogeneity of study designs, reviewing the growing body of research may be synthesized into some broad trends: Ascaris emerges mostly as protective from malaria and its severe manifestations, whereas hookworm seems to increase malaria incidence. As efforts are made to de-worm populations in malaria endemic areas, there is still no clear picture of the impact these programmes have in terms of quantitative and qualitative changes in malaria.

Pathogenic nematodes suppress humoral responses to third-party antigens in vivo by IL-10-mediated interference with Th cell function

One third of the human population is infected with helminth parasites. To promote their longevity and to limit pathology, helminths have developed several strategies to suppress the immune response of their host. As this immune suppression also acts on unrelated third-party Ags, a preexisting helminth infection may interfere with vaccination efficacy. In this study, we show that natural infection with Litomosoides sigmodontis suppressed the humoral response to thymus-dependent but not to thymus-independent model Ags in C57BL/6 mice. Thereby, we provide evidence that reduced humoral responses were mediated by interference with Th cell function rather than by direct suppression of B cells in L. sigmodontis-infected mice. We directly demonstrate suppression of Ag-specific proliferation in OVA-specific Th cells after adoptive transfer into L. sigmodontis-infected mice that led to equally reduced production of OVA-specific IgG. Transferred Th cells displayed increased frequencies of Foxp3(+) after in vivo stimulation within infected but not within naive mice. Helminth-mediated suppression was induced by established L. sigmodontis infections but was completely independent of the individual worm burden. Using DEREG mice, we rule out a central role for host-derived regulatory T cells in the suppression of transferred Th cell proliferation. In contrast, we show that L. sigmodontis-induced, host-derived IL-10 mediated Foxp3 induction in transferred Th cells and significantly contributed to the observed Th cell hypoproliferation within infected mice.

CCL17 controls mast cells for the defense against filarial larval entry

Filarial parasites have to trespass many barriers to successfully settle within their mammalian host, which is equipped with mechanical borders and complex weaponry of an evolved immune system. However, little is known about mechanisms of early local events in filarial infections. In this study, bone marrow-derived dendritic cells not only upregulated activation markers CD40 and CD80 upon in vitro stimulation with filarial extracts, but also secreted CCL17, a chemokine known to be produced upon microbial challenge. Mice deficient for CCL17 had an up to 4-fold higher worm burden compared with controls by day 10 of infection with the murine filaria Litomosoides sigmodontis. Also, numbers of mast cells (MCs) invading the skin and degranulation were significantly increased, which was associated with enhanced vascular permeability and larval establishment. This phenotype was reverted by inhibition of MC degranulation with disodium cromoglycate or by blockade of histamine. In addition, we showed that CCL17-mediated vascular permeability was dependent on the presence of Wolbachia endosymbionts and TLR2. Our findings reveal that CCL17 controls filarial larval entry by limiting MC-dependent vascular permeability.

Filaria-induced IL-10 suppresses murine cerebral malaria

Filarial nematodes achieve long survival in their hosts due to their capacity to modulate immune responses. Therefore, immunomodulation by filarial nematodes may alter responses to concomitant infections such as malaria. Cerebral malaria (CM), a severe complication of Plasmodium falciparum infections, is triggered as a consequence of the immune response developed against malaria parasites. The question arises whether prior infection with helminth parasites is beneficial against CM. In the present work a murine model for subsequent has been used to assess this hypothesis. C57BL/6 mice were infected with the rodent filarial parasite Litomosoides sigmodontis and the murine model parasite for CM, Plasmodium berghei ANKA. Previously filaria-infected C57BL/6 mice showed significantly reduced CM rates. CD8(+) T cell recruitment to the brain, a hallmark for CM development, was reduced in protected mice. Furthermore, in contrast to P. berghei single-infected animals, filaria-infected mice had significantly higher levels of circulating IL-10. The requirement for IL-10 in CM protection was demonstrated by the lack of protection in IL-10 KO mice. This suggests that the anti-inflammatory IL-10 elicited by filarial nematodes is able to suppress the overwhelming inflammatory reaction otherwise triggered against malaria parasites in C57BL/6 mice, preventing full progress to CM.

Co-Infection of cattle with Fasciola hepatica and Mycobacterium bovis- immunological consequences

Fasciola hepatica, the liver fluke, is a common parasite of cattle in much of the world. Previously, we have shown that cattle infected with F. hepatica have altered responsiveness (delayed type hypersensitivity reaction and cytokine responses) to M. bovis BCG infection. We hypothesized that co-infection with F. hepatica would, likewise, alter the immune response of cattle to virulent M. bovis infection, with possible implications for disease diagnosis and disease progression. Our previous work with F. hepatica/M. bovis BCG-infected cattle demonstrated a reduction in interferon (IFN)-gamma responsiveness in co-infected animals. Similar findings are reported here with virulent M. bovis following aerosol infection. The epidemiological significance of these findings, also, require exploration, particularly in view of the considerable resources devoted to the diagnosis and eradication of bovine tuberculosis, and the high prevalence of F. hepatica infection in areas where eradication has proved difficult.

New insights into the biology of filarial infections

Recent successes in the control of lymphatic filariasis and onchocerciasis need continuing research in order to sustain the achievements and to develop further tools to tackle the new questions that arise when only reduced infection prevalences prevail. In this regard, in a symposium held at the Xth European Multicolloquium of Parasitology (August 2008, Paris) questions such as the impact of filarial immunosuppression, and its lack following filarial control, on the outcome of co-infections were addressed, as were new approaches to treatment with promising drugs such as moxidectin or the antibiotic chemotherapy against Wolbachia endosymbionts in filariae. In particular, longer treatment courses of doxycycline could be carried out by community-directed treatment at high coverage, thus potentially allowing its use in restricted areas with suboptimal responses to ivermectin against onchocerciasis, or in areas with co-infection by loiasis where onchocerciasis or lymphatic filariasis need to be controlled. New, more potent drugs, or eventually vaccines, will be of importance because in many vector–filarial parasite relationships worldwide, transmission efficacy increases with low numbers of ingested microfilariae, and since ivermectin may render treated hosts more susceptible to new infection.