Influence of Brugia malayi life stages and BmAFII fraction on experimental Leishmania donovani infection in hamsters

Wuchereria bancrofti infection is associated with progression to clinical visceral leishmaniasis in VL- endemic areas in Muzaffarpur, Bihar, India

BACKGROUND

Co-endemicity of neglected tropical diseases (NTDs) necessitates that these diseases should be considered concomitantly to understand the relationship between pathology and to support disease management and control programs. The aims of the study were to assess the prevalence of filarial infection in asymptomatic Leishmania donovani infected individuals and the correlation of Wuchereria bancrofti infection with progression to clinical visceral leishmaniasis (VL) in Bihar, India.

METHODOLOGY/PRINCIPAL FINDINGS

Within the Muzaffarpur-TMRC Health and Demographic Surveillance System (HDSS) area, a cohort of Leishmania seropositive (n = 476) or seronegative individuals (n = 1130) were sampled annually for three years for filarial infection and followed for progression to clinical VL. To corroborate the results from the cohort study, we also used a retrospective case-control study of 36 VL cases and 71 controls selected from a subset of the HDSS population to investigate the relationship between progression to clinical VL and the prevalence of filarial infection at baseline. Our findings suggest a higher probability of progression to clinical VL in individuals with a history of filarial infection: in both the cohort and case-control studies, progression to clinical VL was higher among filaria infected individuals (RR = 2.57, p = 0.056, and OR = 2.52, p = 0.046 respectively).

CONCLUSION

This study describes that progression to clinical VL disease is associated with serological evidence of prior infection with W. bancrofti. The integration of disease programs for Leishmania and lymphatic filariasis extend beyond the relationship of sequential or co-infection with disease burden. To ensure elimination targets can be reached and sustained, we suggest areas of co-endemicity would benefit from overlapping vector control activities, health system networks and surveillance infrastructure.

Fragment-Based Drug Discovery against Mycobacteria: The Success and Challenges

The emergence of drug-resistant mycobacteria, including Mycobacterium tuberculosis (Mtb) and non-tuberculous mycobacteria (NTM), poses an increasing global threat that urgently demands the development of new potent anti-mycobacterial drugs. One of the approaches toward the identification of new drugs is fragment-based drug discovery (FBDD), which is the most ingenious among other drug discovery models, such as structure-based drug design (SBDD) and high-throughput screening. Specialized techniques, such as X-ray crystallography, nuclear magnetic resonance spectroscopy, and many others, are part of the drug discovery approach to combat the Mtb and NTM global menaces. Moreover, the primary drawbacks of traditional methods, such as the limited measurement of biomolecular toxicity and uncertain bioavailability evaluation, are successfully overcome by the FBDD approach. The current review focuses on the recognition of fragment-based drug discovery as a popular approach using virtual, computational, and biophysical methods to identify potent fragment molecules. FBDD focuses on designing optimal inhibitors against potential therapeutic targets of NTM and Mtb (PurC, ArgB, MmpL3, and TrmD). Additionally, we have elaborated on the challenges associated with the FBDD approach in the identification and development of novel compounds. Insights into the applications and overcoming the challenges of FBDD approaches will aid in the identification of potential therapeutic compounds to treat drug-sensitive and drug-resistant NTMs and Mtb infections.

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.

Lymphatic filariasis and visceral leishmaniasis coinfection: A review on their epidemiology, therapeutic, and immune responses

Coinfection is less commonly observed in individuals around the world, yet it is more common than the single infection. Around 800 million people worldwide are infected with helminths as a result of various diseases. Lymphatic filariasis (LF) and visceral leishmaniasis (VL) are chronic, deadly, crippling, and debilitating neglected tropical diseases (NTDs) that are endemic in tropical and subtropical regions of the world. Due to poor hygienic conditions, poverty, and genetic predisposition, those living in endemic areas are more likely to develop both leishmaniasis and filariasis. One of the key challenges in the management of LF/VL coinfection is the development of an effective therapeutic strategy that not only treats the first episode of VL but also prevents LF. However, there is a scarcity of knowledge and data on the relationship between LF and VL coinfection. While reviewing it was apparent that only a few studies relevant to LF/VL coinfections have been reported from southeastern Spain, Sudan, and the Indian subcontinents, highlighting the need for greater research in the most affected areas. We also looked at LF and VL as a single disease and also as a coinfection. Some features of the immune response evolved in mammalian hosts against LF and VL alone or against coinfection are also discussed, including epidemiology, therapeutic regimens, and vaccines. In addition to being potentially useful in clinical research, our findings imply the need for improved diagnostic methodology and therapeutics, which could accelerate the deployment of more specific and effective diagnosis for treatments to lessen the impact of VL/LF coinfections in the population.

Cross-protective efficacy of immuno-stimulatory recombinant Brugia malayi protein HSP60 against the Leishmania donovani in BALB/c mice

Coinfection of Leishmania with bacteria, viruses, protozoans, and nematodes alter the immune system of the host, thereby influencing the disease outcomes. Here, we have determined the immunogenic property and protective efficacy of the cross-reactive molecule HSP60 of filarial parasite B. malayi against the L. donovani in BALB/c mice. Parasitological parameters results showed a significant decrease in the parasite burden (~59%; P < 0.001) and also a substantial increase in the delayed-type hypersensitivity (DTH) response (P < 0.001) in mice immunized with 10 μg of rBmHSP60. Protection against L. donovani in mice immunized with rBmHSP60 resulted from activation of the T cells, which is characterized by higher levels of nitric oxide (NO) production, enhanced cell proliferation, higher levels (expression and release) of IFN- γ, TNF- α, and IL-12, also, higher production of IgG and IgG2a antibodies. This strong Th1 immune response creates an inflammatory domain for L. donovani and protects the host from VL.

Boosting immunity to treat parasitic infections: Asaia bacteria expressing a protein from Wolbachia determine M1 macrophage activation and killing of Leishmania protozoans

Leishmaniases are severe vector-borne diseases affecting humans and animals, caused by Leishmania protozoans. Over one billion people and millions of dogs live in endemic areas for leishmaniases and are at risk of infection. Immune polarization plays a major role in determining the outcome of Leishmania infections: hosts displaying M1-polarized macrophages are protected, while those biased on the M2 side acquire a chronic infection that could develop into a deadly disease. The identification of the factors involved in M1 polarization is essential for the design of therapeutic and prophylactic interventions, including vaccines. Infection by the filarial nematode Dirofilaria immitis could be one of the factors that interfere with leishmaniasis in dogs. Indeed, filarial nematodes induce a partial skew of the immune response towards M1, likely caused by their bacterial endosymbionts, Wolbachia. Here we have examined the potential of Asaia^WSP, a bacterium engineered for the expression of the Wolbachia surface protein (WSP), as an inductor of M1 macrophage activation and Leishmania killing. Macrophages stimulated with Asaia^WSP displayed a strong leishmanicidal activity, comparable to that determined by the choice-drug amphotericin B. Additionally, Asaia^WSP determined the expression of markers of classical macrophage activation, including M1 cytokines, ROS and NO, and an increase in phagocytosis activity. Asaia not expressing WSP also induced macrophage activation, although at a lower extent compared to Asaia^WSP. In summary, the results of the present study confirm the immunostimulating properties of WSP highlighting a potential therapeutic efficacy against Leishmania parasites. Furthermore, Asaia was designed as a delivery system for WSP, thus developing a novel type of immunomodulating agent, worthy of being investigated for immuno-prophylaxis and -therapy of leishmaniases and other diseases that could be subverted by M1 macrophage activation.

Meta-taxonomic analysis of prokaryotic and eukaryotic gut flora in stool samples from visceral leishmaniasis cases and endemic controls in Bihar State India

Visceral leishmaniasis (VL) caused by Leishmania donovani remains of public health concern in rural India. Those at risk of VL are also at risk of other neglected tropical diseases (NTDs) including soil transmitted helminths. Intestinal helminths are potent regulators of host immune responses sometimes mediated through cross-talk with gut microbiota. We evaluate a meta-taxonomic approach to determine the composition of prokaryotic and eukaryotic gut microflora using amplicon-based sequencing of 16S ribosomal RNA (16S rRNA) and 18S rRNA gene regions. The most abundant bacterial taxa identified in faecal samples from Bihar State India were Prevotella (37.1%), Faecalibacterium (11.3%), Escherichia-Shigella (9.1%), Alloprevotella (4.5%), Bacteroides (4.1%), Ruminococcaceae UCG-002 (1.6%), and Bifidobacterium (1.5%). Eukaryotic taxa identified (excluding plant genera) included Blastocystis (57.9%; Order: Stramenopiles), Dientamoeba (12.1%; Family: Tritrichomonadea), Pentatrichomonas (10.1%; Family: Trichomonodea), Entamoeba (3.5%; Family: Entamoebida), Ascaridida (0.8%; Family: Chromodorea; concordant with Ascaris by microscopy), Rhabditida (0.8%; Family: Chromodorea; concordant with Strongyloides), and Cyclophyllidea (0.2%; Order: Eucestoda; concordant with Hymenolepis). Overall alpha (Shannon's, Faith's and Pielou's indices) and beta (Bray-Curtis dissimilarity statistic; weighted UniFrac distances) diversity of taxa did not differ significantly by age, sex, geographic subdistrict, or VL case (N = 23) versus endemic control (EC; N = 23) status. However, taxon-specific associations occurred: (i) Ruminococcaceae UCG- 014 and Gastranaerophilales_uncultured bacterium were enriched in EC compared to VL cases; (ii) Pentatrichomonas was more abundant in VL cases than in EC, whereas the reverse occurred for Entamoeba. Across the cohort, high Escherichia-Shigella was associated with reduced bacterial diversity, while high Blastocystis was associated with high bacterial diversity and low Escherichia-Shigella. Individuals with high Blastocystis had low Bacteroidaceae and high Clostridiales vadin BB60 whereas the reverse held true for low Blastocystis. This scoping study provides useful baseline data upon which to develop a broader analysis of pathogenic enteric microflora and their influence on gut microbial health and NTDs generally.

Recombinant Calponin of human filariid Brugia malayi: Secondary structure and immunoprophylactic potential

In the search for potential vaccine candidates for the control of human lymphatic filariasis, we recently identified calponin-like protein, that regulates actin/myosin interactions, in a proinflammatory fraction F8 (45.24-48.64kDa) of Brugia malayi adult worms. In the present study, the gene was cloned, expressed, and the recombinant Calponin of B. malayi (r-ClpBm) was prepared and characterized. r-ClpBm bears homology with OV9M of Onchocerca volvulus, a non-lymphatic filariid that causes loss of vision and cutaneous pathology. r-ClpBm was found to be a ∼45kDa protein that folds into a predominantly α-helix conformation. The protective efficacy of r-ClpBm against B. malayi infection in Mastomys coucha was investigated by assessing the course of microfilaraemia and adult worm burden in the host immunized with r-ClpBm and subsequently infected with infective third stage larvae (L3). Expression of the Calponin was detected in all life stages (microfilariae, L3, L4, L5 and adults) of the parasite and immunization with r-ClpBm partially protected M. coucha against establishment of infection as inferred by ∼42% inhibition in parasite burden. Upregulated cellular proliferation, TNF-α, IFN-γ, IL-1β, IL-4, nitric oxide (NO) release, expression of iNOS, and specific IgG, IgG1 and IgG2b in immunized animals correlated with parasitological findings. r-ClpBm immunization caused degranulation in majority of mast cells indicating possible involvement of mast cell products in reducing the parasite survival. It appears that complex mechanisms including Th1, Th2, NO and mast cells are involved in the clearance of infection. To the best of our knowledge this is the first report on cloning, expression of the gene and purification of r-ClpBm, determination of its secondary structure and its ability to partially prevent establishment of B. malayi infection. Thus, r-ClpBm may further be studied and developed in combination with other protective molecules of B. malayi as a component of potential filarial cocktail vaccine candidate.

Detection for cross-reactive proteins in filarial worm Setaria equina, MCF-7 human breast cancer, and Huh-7 hepatoma cells

This study aimed to detect the cross-reactive proteins in filarial parasite adult worm Setaria equina and two different tumor cell lines (MCF-7 human breast cancer and Huh-7 hepatoma cells). This was performed using rabbit anti-S. equina extract (SeqE) or DEC (Diethylcarbamazine citrate) polyclonal IgG antibodies by indirect ELISA and western blotting. The results indicated cross-reactive bands at 70 and 75 kDa in all extracts by anti-DEC and SeqE antibodies, respectively. In addition, the expression of 70 kDa protein was only reduced in filarial worms and Huh-7 after in vitro DEC treatment compared to the control.

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.

Protection against filarial infection by 45-49 kDa molecules of Brugia malayi via IFN-γ-mediated iNOS induction

Nitric oxide (NO) mediated mechanisms have been implicated in killing of some life-stages of Brugia malayi/Wuchereria bancrofti and protect the host through type 1 responses and IFN-γ stimulated toxic mediators' release. However, the identity of NO stimulating molecules of the parasites is not known. Three predominantly NO-stimulating SDS-PAGE resolved fractions F8 (45.24-48.64 kDa), F11 (33.44-38.44 kDa) and F12 (28.44-33.44 kDa) from B. malayi were identified and their proteins were analyzed by 2-DE and MALDI-TOF/TOF. Tropomyosin, calponin and de novo peptides were identified by 2-DE and MALDI-TOF/TOF in F8 and immunization with F8 conferred most significant protection against L3-initiated infection in Mastomys coucha. Immunized animals showed upregulated F8-induced NO, IFN-γ, TNF-α, IL-1β, IL-10, TGF-β release, cellular proliferative responses and specific IgG and IgG1. Anti-IFN-γ, anti-TNF-α, and anti-IL-1β significantly reduced F8-mediated NO generation and iNOS induction at protein levels. Anti-IFN-γ treated cells showed maximum reduction (>74%) in NO generation suggesting a predominant role of IFN-γ in iNOS induction. In conclusion, the findings suggest that F8 which contains tropomyosin, calponin and de novo peptides protects the host via IFN-γ mediated iNOS induction and may hold promise as vaccine candidate(s). This is also the first report of identification of tropomyosin and calponin in B. malayi.

Apoptotic mechanisms are involved in the death of Strongyloides venezuelensis after triggering of nitric oxide

Despite progress in understanding the role of nitric oxide (NO) in the pathogenesis of helminth infections, the role in strongyloidosis is unknown. Firstly, we studied the production of NO in mice infected with Strongyloides venezuelensis as well as in macrophage cultures stimulated with parasite antigens. Somatic larvae 3 (L3) and excretory-secretory female antigens stimulate specific NO production measured by Griess reaction and expression of inducible NO synthase by RT-PCR and quantitative PCR. Moreover, mice infected with S. venezuelensis produce NO in migration stages. Secondly, we analysed the effect of NO production on L3 and females of S. venezuelensis using NO donors such as diethylenetriamine and 3,3-bis(aminoethyl)-1-hydroxy-2-oxo-1-triazene. Parasites died after NO donor treatment in a dose-dependent manner. Finally, apoptotic mechanisms are involved in the death of S. venezuelensis larvae.

Heat shock protein 60 of filarial parasite Brugia malayi: cDNA cloning, expression, purification and in silico modeling and analysis of its ATP binding site

We report here cloning and expression of full length mitochondrial HSP60 gene of Brugia malayi adult worm (mtHSP60bm), purification of the gene product by affinity chromatography, its in silico 3D structure and the sequence homology of the protein with Escherichia coli GroEL/ES and human HSP60. The ATP binding pocket of human HSP60 and mtHSP60bm were analyzed and compared using in silico models. The distribution of HSP60 in different life-stages of the parasite was determined using antibodies raised against recombinant mtHSP60bm (rmtHSP60bm). mtHSP60bm was present in all life-stages of the parasite except third stage infective larvae, in which it could be induced by heat-shock, and showed high degree of homology with E. coli GroEL/ES. The ATP binding pocket of HSP60 in humans, E. coli and B. malayi were also found structurally conserved. This similarity between human and mtHSP60bm might be useful in understanding the host-parasite interactions. This is the first ever report on distribution, cloning, sequence homology and ATP binding site of mtHSP60bm.

Sufficiency of a single administration of filarial antigens adsorbed on polymeric lamellar substrate particles of poly (L-lactide) for immunization

A majority of antigens require repeated administration to ensure development of adequate humoral and cell mediated immune response. To minimize the number of administrations required, we investigated the utility of biodegradable polymeric lamellar substrate particles of poly (l-lactide) (PLSP) as adjuvant for filarial antigen preparations. PLSP was prepared and characterized and Brugia malayi adult worm extract (BmA) and its SDS-PAGE resolved 54-68 kDa fraction F6 were adsorbed on to PLSP. Swiss mice received a single injection of PLSP-F6, PLSP-BmA, FCA-F6, FCA-BmA and two doses of the plain antigens. Specific IgG, IgG1, IgG2a, IgG2b and IgE levels in serum, IFN-γ, TNF-α and nitric oxide (NO) release from cells of the immunized animals in response to antigen challenge were studied. The average size of PLSP particles was <10 μm and its % antigen adsorption efficacy was 60.4, 55.2 and 61.6 for BSA, BmA and F6, respectively. Single injection of PLSP-F6 or PLSP-BmA produced better immune responses compared to one injection of FCA-F6/BmA or two injections of plain F6 or BmA. Moreover, PLSP-F6 produced much better response than PLSP-BmA. These data demonstrate for the first time that PLSP is a superior immunoadjuvant for enhancing the immune response to filarial BmA and F6 molecules and obviates the need for multiple immunization injections.