Vaccination with neutrophil inhibitory factor reduces the fecundity of the hookworm Ancylostoma ceylanicum

Functional Diversity of the Excretory/Secretory Proteins of Nematode Parasites

INTRODUCTION

Parasites release a wide array of protein as excretory and secretory products (ESPs). Irrespective of their mode of propagation, ESPs are found to be secreted or excreted by both naturally occurring and laboratory-cultivated parasites. Mass spectrometry-based approaches have been extensively used to identify and characterize the ESP constituents. ESPs are involved in various cellular activities such as immune modulation, proteolysis, inhibition of proteases and protection of cells against oxidants. Specifically, their role in host immune evasion by down-regulation of pro-inflammatory cytokines and up-regulation of anti-inflammatory cytokines attracts scientific attention. A thorough investigation of functional diversity of ESPs may be helpful in planning control strategies against many parasites.

METHODS

This review focuses on diversity of ES proteins, various approaches to identify them and discusses about the biochemical and functional aspects of such proteins.

RESULTS

The diverse array of proteins secreted or excreted (a, GST-1, acetylcholinesterase, GAPDH) by the parasites are also described emphasizing their role in cellular physiology.

CONCLUSION

Finally, it concludes by citing some of these proteins as potential therapeutic agents against helminth challenge.

Hookworm infections: Reappraising the evidence for a role of Neutrophils in light of NETosis

In Hookworm infection, neutrophils have long had the image of the villain, being recruited to the site of larval migration because of damage but participating themselves in tissue injury. With recent developments in neutrophil biology, there is an increasing body of evidence for the role of neutrophils as effector cells in hookworm immunity. In particular, their ability to release extracellular traps, or neutrophil extracellular traps (NETs), confer neutrophils a larvicidal activity. Here, we review recent evidence in this nascent field and discuss the avenue for future research on NETs/hookworm interactions.

Hookworm infection: Toward development of safe and effective peptide vaccines

Hookworms are hematophagous nematode parasites that have infected a billion people worldwide. Anthelmintic drugs have limited efficacy and do not prevent reinfection. Therefore, prophylactic vaccines are in high demand. Whole parasite vaccines are allergic and unsafe; thus, research into subunit vaccines has been warranted. A comprehensive overview of protein or peptide subunit vaccines' safety, protective efficacy, and associated immune responses is provided herein. The differences between the immune responses against hookworm infection by patients from epidemic versus nonepidemic areas are discussed in detail. Moreover, the different immunologic mechanisms of protection are discussed, including those that rely on allergic and nonallergic humoral and antibody-dependent cellular responses. The allergic and autoimmune potential of hookworm antigens is also explored, as are the immunoregulatory responses induced by the hookworm secretome. The potential of oral mucosal immunizations has been overlooked. Oral immunity against hookworms is a long-lived and safer immune response that is associated with elimination of infection and protective against reinfections. However, the harsh conditions of the gastrointestinal environment necessitates special oral delivery systems to unlock vaccines' protective potential. The potential for development of safer and more effective peptide- and protein-based anthelmintic vaccines is explored herein.

TFPR1 acts as an immune regulator and an efficient adjuvant for proteins and peptides by activating immune cells, primarily through TLR2

Triflin, a non-toxic protein found in the venom of the Habu snake, belongs to the CRISP (cysteine-rich secretory protein) family, which comprises two domains: a C-terminal cysteine-rich domain (CRD) and an N-terminal pathogenesis-related-1 (PR-1) domain. The function of the highly structurally conserved PR-1 domain is unknown. Here, we successfully expressed the PR-1 domain of triflin (hereafter called TFPR1) in E. coli. Animal experiments showed that TFPR1 augmented Th1-biased antibody- and cell-mediated immune responses in mice immunized with two protein antigens (OVA and HBsAg) or a peptide antigen (HIV-1 pep). A flow cytometry-based binding assay and in vitro stimulation with TFPR1 showed that it triggered Th1-biased proinflammatory and immunoregulatory cytokine secretion primarily by binding to B cells and macrophages within the mouse splenocyte population. Quantitative RT-PCR, antibody blocking assays using a specific anti-mTLR2 antibody, and stimulatory experiments in vitro using splenocytes from TLR2-KO mice demonstrated that TFPR1 activated murine immune cells, primarily by stimulating toll-like receptor 2 (TLR2). These results suggest that TFPR1 acts as a novel immune modulator and potent adjuvant primarily by activating TLR2. Thus, the PR-1-based core domain might play a role in immune regulation.

Biological role of excretory-secretory proteins in endemic parasites of Latin America and the Caribbean

Neglected tropical diseases (NTDs) share certain traits: they are parasitic infections, prevailing in tropical environments and affecting marginalized sectors of the population. Six NTDs - ascariasis, cysticercosis, echinococcosis, hookworm infection, onchocerciasis and trichuriasis - all of them endemic in Latin America and the Caribbean (LAC), are analysed in this work. This review aims to discuss key information on the function of excretory/secretory (E/S) proteins from these parasites in their infectivity, pathogeny and diagnosis. The modulation of the host immune system to favour the permanence and survival of the parasite is also discussed. An updated knowledge on the function of E/S molecules in endemic parasitoses in LAC may lead to new approaches for the clinical management and diagnosis of these diseases. In turn, this could allow us to optimize their treatment and make it more affordable - a relevant goal given the economic constraints that the region is facing.

Antagonism of CD11b with neutrophil inhibitory factor (NIF) inhibits vascular lesions in diabetic retinopathy

Leukocytes and proteins that govern leukocyte adhesion to endothelial cells play a causal role in retinal abnormalities characteristic of the early stages of diabetic retinopathy, including diabetes-induced degeneration of retinal capillaries. Leukocyte integrin αmβ2 (CD11b/CD18, MAC1), a protein mediating adhesion, has been shown to mediate damage to endothelial cells by activated leukocytes in vitro. We hypothesized that Neutrophil Inhibitory Factor (NIF), a selective antagonist of integrin αmβ2, would inhibit the diabetes-induced degeneration of retinal capillaries by inhibiting the excessive interaction between leukocytes and retinal endothelial cells in diabetes. Wild type animals and transgenic animals expressing NIF were made diabetic with streptozotocin and assessed for diabetes-induced retinal vascular abnormalities and leukocyte activation. To assess if the leukocyte blocking therapy compromised the immune system, animals were challenged with bacteria. Retinal superoxide production, leukostasis and leukocyte superoxide production were increased in wild type mice diabetic for 10 weeks, as was the ability of leukocytes isolated from diabetic animals to kill retinal endothelial cells in vitro. Retinal capillary degeneration was significantly increased in wild type mice diabetic 40 weeks. In contrast, mice expressing NIF did not develop any of these abnormalities, with the exception that non-diabetic and diabetic mice expressing NIF generated greater amounts of superoxide than did similar mice not expressing NIF. Importantly, NIF did not significantly impair the ability of mice to clear an opportunistic bacterial challenge, suggesting that NIF did not compromise immune surveillance. We conclude that antagonism of CD11b (integrin αmβ2) by NIF is sufficient to inhibit early stages of diabetic retinopathy, while not compromising the basic immune response.

Granulocytes: effector cells or immunomodulators in the immune response to helminth infection?

Granulocytes are effector cells in defence against helminth infections. We review the current evidence for the role of granulocytes in protective immunity against different helminth infections and note that for each parasite species the role of granulocytes as effector cells can vary. Emerging evidence also points to granulocytes as immunomodulatory cells able to produce many cytokines, chemokines and modulatory factors which can bias the immune response in a particular direction. Thus, the role of granulocytes in an immunomodulatory context is discussed including the most recent data that points to an important role for basophils under this guise.

Proteomic analysis of Schistosoma mansoni proteins released during in vitro miracidium-to-sporocyst transformation

Free-living miracidia of Schistosoma mansoni, upon penetration of the their snail intermediate host, undergo dramatic morphological and physiological changes as they transform to the parasitic sporocyst stage. During this transformation process, developing larvae release a diverse array of proteins, herein referred to as larval transformation proteins (LTPs), some of which are postulated to serve a parasite protective function. In the present study, nanoLC-tandem MS analysis was performed on all proteins represented in entire 1-dimensional SDS-PAGE-separated samples in order to gain a more comprehensive picture of the protein constituents associated with miracidium-to-sporocyst transformation and thus, their potential role in influencing establishment of intramolluscan infections. Of 127 proteins with sufficient peptide/sequence information, specific identifications were made for 99, while 28 represented unknown or hypothetical proteins. Nineteen percent of identified proteins possessed signal peptides constituting a cohort of classical secretory proteins, while 22% were identified as putative nonclassically secreted leaderless proteins based on SecretomeP analysis. Proteins comprising these groups consisted mainly of proteases/protease inhibitors, small HSPs, redox/antioxidant enzymes, ion-binding proteins including those with anti-oxidant Fe-binding activities (ferritins, heme-binding protein), and venom allergen-like (VAL) proteins. A polyclonal antibody generated against whole LTPs recognized proteins primarily associated with the cilia, ciliated epidermal plates and intercellular ridges of miracidia and the tegument of fully transformed sporocysts, identifying these structures as sources of a subset of LTPs. Thus lysis of plates and/or leakage during formation of the sporocyst syncytium likely represent significant contributors to the overall LTP makeup, especially identified nonsecretory proteins. However, as plate release/degradation and tegument formation are part of the normal developmental process, all LTPs regardless of tissue origin, would be expected at the parasite-host interface upon infection. This study significantly expands the repertoire of LTPs associated with larval transformation and identifies several, e.g., those involved in stress responses, proteolysis/inhibition, antioxidant and detoxication, and immune modulation, that may play a parasite protective role during this crucial period of transition.

Developmentally regulated expression, alternative splicing and distinct sub-groupings in members of the Schistosoma mansoni venom allergen-like (SmVAL) gene family

Background

The Sperm-coating protein/Tpx-1/Ag5/PR-1/Sc7 (SCP/TAPS) domain is found across phyla and is a major structural feature of insect allergens, mammalian sperm proteins and parasitic nematode secreted molecules. Proteins containing this domain are implicated in diverse biological activities and may be important for chronic host/parasite interactions.

Results

We report the first description of an SCP/TAPS gene family (Schistosoma mansoni venom allergen-like (SmVALs)) in the medically important Platyhelminthes (class Trematoda) and describe individual members' phylogenetic relationships, genomic organization and life cycle expression profiles. Twenty-eight SmVALs with complete SCP/TAPS domains were identified and comparison of their predicted protein features and gene structures indicated the presence of two distinct sub-families (group 1 & group 2). Phylogenetic analysis demonstrated that this group 1/group 2 split is zoologically widespread as it exists across the metazoan sub-kingdom. Chromosomal localisation and PCR analysis, coupled to inspection of the current S. mansoni genomic assembly, revealed that many of the SmVAL genes are spatially linked throughout the genome. Quantitative lifecycle expression profiling demonstrated distinct SmVAL expression patterns, including transcripts specifically associated with lifestages involved in definitive host invasion, transcripts restricted to lifestages involved in the invasion of the intermediate host and transcripts ubiquitously expressed. Analysis of SmVAL6 transcript diversity demonstrated statistically significant, developmentally regulated, alternative splicing.

Conclusion

Our results highlight the existence of two distinct SCP/TAPS protein types within the Platyhelminthes and across taxa. The extensive lifecycle expression analysis indicates several SmVAL transcripts are upregulated in infective stages of the parasite, suggesting that these particular protein products may be linked to the establishment of chronic host/parasite interactions.

The mucosal cellular response to infection with Ancylostoma ceylanicum

Although hookworms are known to stimulate inflammatory responses in the intestinal mucosa of their hosts, there is little quantitative data on this aspect of infection. Here we report the results of experiments conducted in hamsters infected with Ancylostoma ceylanicum. Infection resulted in a marked increase in goblet cells in the intestinal mucosa, which was dependent on the number of adult worms present and was sustained as long as worms persisted (over 63 days) but returned to baseline levels within 7 days of the removal of worms by treatment with ivermectin. Increased mast cell responses were also recorded. Levels were again dependent on the intensity of worm burdens and lasted as long as 63 days after infection. When worms were eliminated, mast cell numbers took over 2 weeks to return to normal. Paneth cell numbers fell soon after infection, the degree of reduction being dependent on the worm burden. After clearance of worms, Paneth cell numbers returned to normal within a week, but then rebounded and numbers rose to higher levels than those in control naïve animals. The time course of the response was similar whether animals experienced a chronic low-intensity infection without loss of worms or a higher intensity infection during the course of which worm burdens were gradually reduced. Clearly, A. ceylanicum was able to induce a marked inflammatory response in its host's intestine which was sustained for over 9 weeks after infection, and which hamsters appeared able to tolerate well. Our data draw attention to the resilience of hookworms which, unlike many other nematodes, are able to survive for many weeks in a highly inflamed intestinal tract.

Host cytokine production, lymphoproliferation, and antibody responses during the course of Ancylostoma ceylanicum infection in the Golden Syrian hamster

The Syrian Golden hamster (Mesocricetus auratus) has been used to model infections with the hookworm Ancylostoma ceylanicum. New molecular immunological reagents to measure cellular immune responses in hamsters were developed and used to determine the impact of A. ceylanicum hookworm infection on host cytokine responses and lymphoproliferation. Initial larval infection with 100 third-stage A. ceylanicum larvae resulted in predominant Th1 responses (upregulation of proinflammatory cytokines) that lasted for the duration of larval migration and continued up to 14 days postinfection (prepatency). Subsequently, development of larvae into egg-laying adult hookworms (patency) coincided with a switch to Th2 predominant responses (interleukin-4 [IL-4]) as well as a marked increase in IL-10 production. This switch also concurred with reduced host lymphoproliferative responses to hookworm antigens. The findings demonstrate a similarity in immune responses between hamsters and humans infected with hookworms, suggesting that hamsters will be a useful animal model species for examining host immunity to human hookworm infections.

The immunoepidemiology of human hookworm infection

Advances in hookworm immunoepidemiology are reviewed. Recent studies demonstrate a mixed Th1/Th2 response in human hookworm infection, with immunosuppression of specific and nonspecific IFN-gamma responses. There is increasing evidence for protective immunity in human hookworm infection, including anti-larval IL-5- and IgE-dependent mechanisms, and for immunological interactions between hookworm infection and other diseases.

Helminth vaccines: from mining genomic information for vaccine targets to systems used for protein expression

The control of helminth diseases of people and livestock continues to rely on the widespread use of anti-helminthic drugs. However, concerns with the appearance of drug resistant parasites and the presence of pesticide residues in food and the environment, has given further incentive to the goal of discovering molecular vaccines against these pathogens. The exponential rate at which gene and protein sequence information is accruing for many helminth parasites requires new methods for the assimilation and analysis of the data and for the identification of molecules capable of inducing immunological protection. Some promising vaccine candidates have been discovered, in particular cathepsin L proteases from Fasciola hepatica, aminopeptidases from Haemonchus contortus, and aspartic proteases from schistosomes and hookworms, all of which are secreted into the host tissues or into the parasite intestine where they play important roles in host-parasite interactions. Since secreted proteins, in general, are exposed to the immune system of the host they represent obvious candidates at which vaccines could be targeted. Therefore, in this article, we consider the potential values and uses of algorithms for characterising cDNAs amongst the collated helminth genomic information that encode secreted proteins, and methods for their selective isolation and cloning. We also review the variety of prokaryotic and eukaryotic cell expression systems that have been employed for the production and downstream purification of recombinant proteins in functionally active form, and provide an overview of the parameters that must be considered if these recombinant proteins are to be commercialised as vaccine therapeutics in humans and/or animals.

Parasitic nematode interactions with mammals and plants

Parasitic nematodes that infect humans, animals, and plants cause serious diseases that are deleterious to human health and agricultural productivity. Chemical and biological control methods have reduced the impact of these parasites. However, surviving environmental stages lead to persistent reinfection of host species. In addition, development of resistance to nematicides and anthelmintics by these parasites and reduced availability of some nematicides, for environmental protection, pose significant obstacles for current and future prospects of effective parasite control. Due to marked differences in host species, research on animal and plant parasitic nematodes often proceeds independently. Despite the differences between animals and plants, basic cellular properties are shared among these host organisms. Some common properties may be important for mechanisms [homologous or convergent (homoplastic)] by which nematodes successfully infect these diverse hosts or by which animal and plant hosts resist infections by these pathogens. Here we compare host/parasite interactions between plant parasitic nematodes (PPN) and animal parasitic nematodes, with an emphasis on mammalian hosts (MPN). Similarities and differences are considered in the context of progress on molecular dissection of these interactions. A comprehensive coverage is not possible in the space allotted. Instead, an illustrative approach is used to establish examples that, it is hoped, exemplify the value of the comparative approach.

A family of activation associated secreted protein (ASP) homologues of Cooperia punctata

Activation-associated secreted proteins (ASP) of nematodes have been studied as potential vaccine components. In this study we report the cloning and analysis of cDNA and genomic sequences of Cooperia punctata and establish the presence of two 75% identical ASP-1 genes in C. punctata. Additional C. punctata ASP paralogues were shown to be present. Analysis of PCR products amplified from genomic DNA from a pool of worms revealed extensive sequence diversity within this family of proteins, reflecting the presence of different ASP paralogues in a single worm as well as extensive polymorphisms between different worms. ASP proteins contain a conserved region called the sperm-coating protein (SCP) domain of unknown function, which is present as a single copy in proteins from yeast and a wide range of multi-cellular organisms. Only in three nematodes has a protein composed of duplicated SCP-domains been identified. C. punctata is the first organism in which at least two such genes are found. Database searches identified similarity of the C-terminal cysteine-rich domain of ASP proteins to a nematode metallothionein motif. Cp-asp-1b was expressed in Escherichia coli and both the N-terminal and C-terminal domain were shown to be recognized by sera of C. punctata infected bovines. The description of the asp gene family of C. punctata provides the basis for more detailed studies into the extent of variation and immunological recognition of this family that may assist in rational vaccine design.

Effect of vaccinations with recombinant fusion proteins on Ancylostoma caninum habitat selection in the canine intestine

Laboratory dogs were vaccinated subcutaneously with 3 different recombinant fusion proteins, each precipitated with alum or calcium phosphate. The vaccinated dogs were then challenged orally with 400 third-stage infective larvae (L3) of the canine hookworm, Ancylostoma caninum. The 3 A. caninum antigens selected were Ac-TMP, an adult-specific secreted tissue inhibitor of metalloproteases; Ac-AP, an adult-specific secreted factor Xa serine protease inhibitor anticoagulant; and Ac-ARR-1, a cathepsin D-like aspartic protease. Each of the 3 groups comprised 6 male beagles (8 +/- 1 wk of age). A fourth group comprised control dogs injected with alum. All of the dogs vaccinated with Ac-TMP or Ac-APR-1 exhibited a vigorous antigen-specific antibody response, whereas only a single dog vaccinated with Ac-AP developed an antibody response. Dogs with circulating antibody responses exhibited 4.5-18% reduction in the numbers of adult hookworms recovered from the small intestines at necropsy, relative to alum-injected dogs. In contrast, there was a concomitant increase in the number of adult hookworms recovered from the colon. The increase in colonic hookworms was as high as 500%, relative to alum-injected dogs. Female adult hookworms were more likely to migrate into the colon than were males. Anti-enzyme and anti-enzyme inhibitor antibodies correlated with an alteration in adult hookworm habitat selection in the canine gastroinntestinal tract.