Year : 2014 | Volume
: 7 | Issue : 2 | Page : 93--103
Heat shock proteins and parasitic diseases: Part 1: Helminths
Sherif M Abaza
Department of Parasitology, Faculty of Medicine, Suez Canal University, Ismailia, Egypt
Sherif M Abaza
Department of Parasitology, Faculty of Medicine, Suez Canal University, Ismailia
Heat shock proteins (HSPs) are highly conserved and immunogenic proteins that are shared among diverse groups of mammals and microbial agents. They are categorized into different families according to their molecular weight. HSPs are involved in a variety of cellular processes and essential to cell survival. They are also implicated in immune pathology and clinical manifestations of a variety of autoimmune diseases and/or metabolic disorders such as atherosclerosis, diabetes and systemic lupus erythematosus. Their role in antigen cross-presentation and cancer immunotherapy as well as initiators of immune response and targets of autoimmune attack was also reported.
The objectives of the current presentation are to summarize the functional properties of HSPs and their role in innate and acquired immune responses, to throw light on their role in pathogenesis and parasites survival, to review the literature searching for new drug discovery and vaccine candidates for parasitic diseases, and finally to present their use in diagnosis and genotyping of some parasitic diseases.
Heat shock proteins (HSPs) are highly conserved and immunogenic proteins that are shared
1. Functional Properties of HSPs
1.1. Innate immunity
1.2. Adaptive immunity:
1.3. HSPs as cancer vaccines:
1.4. HSPs as infectious disease vaccines
1.5. HSPs and apoptosis
2. Heat Shock Proteins and Helminthes
2.1. Schistosoma spp.
2.2. Echinococcus spp.
2.3. Strongyloides spp.
2.4. Trichinella spiralis
2.5. Filarial nematodes
2.6. Other helminthes
Abbreviations: APC: Antigen-presenting cell; CTL: Cytotoxic T-lymphocyte; E/S: Excretory/secretory; gp96: a member of HSP90 family; GST: Glutathione-S-transferase; HC: Hydatid cyst; HSP: Heat shock protein; IFN: Interferon; IL: Interleukin; MHC: major histocompatibility complex; NK: Natural killer; SEA: Soluble egg antigen; TLR: Toll-like receptor; TGF: Transforming growth factor; TNF: Tumor necrosis factor.
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Abaza SM. Heat shock proteins and parasitic diseases: Part 1: Helminths.Parasitol United J 2014;7:93-103
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Abaza SM. Heat shock proteins and parasitic diseases: Part 1: Helminths. Parasitol United J [serial online] 2014 [cited 2023 Feb 1 ];7:93-103
Available from: http://www.new.puj.eg.net/text.asp?2014/7/2/93/149556
Stress proteins or heat-shock proteins (HSPs) are among the highly conserved and immunogenic proteins shared among diverse groups of mammals and microbial agents  . HSPs were first recognized when the temperature of an incubator housing Drosophila was elevated, resulting in a change in the pattern of chromosomal puffing within the salivary glands  . In addition to heat, these proteins were found to be inducible upon exposure to a range of environmental stresses including oxygen deprivation, pH extremes, and nutrient deprivation  . HSP synthesis occurs at 5-15°C above the optimal organism temperature depending on its growth temperature range  . Generally, there is a transient increase in HSPs synthesis at a low level of temperature elevation, with a more sustained response observed at higher temperatures, a pattern of response observed in numerous organisms. For example, heat shock of BCG by increasing the temperature to 42°C results in the production of both HSP65 and HSP70, whereas HSP70 synthesis is more pronounced at 45°C. The investigators added that both heat-shock response and upregulation of HSPs are observed in all tissues and in both prokaryotic and eukaryotic organisms, indicating that it is a ubiquitous and critical biological response  .
These proteins have been categorized into different families according to their molecular weight, for example HSP110, HSP90, HSP70, HSP60, HSP40, HSP20-30, and HSP10 , . For uniformity, Kampinga et al.  proposed guidelines for the nomenclature of various human HSP families. However, HSPs could be categorized into different functional systems, with some overlap. The HSP60-HSP10 system is involved in classical protein folding, whereas the HSP70-HSP40 system stabilizes peptides in a linear, unfolded state and delivers them to the HSP60-HSP10 system  . The HSP90 family is found predominantly in the cytoplasm and is believed to mediate the folding of specialized proteins such as steroid receptors and protein kinases  . Thermal tolerance, disaggregation, and unfolding of aggregated proteins for enzymatic digestion are handled by the larger HSP100  . Being involved in such a variety of cellular processes, it is not surprising that the majority of HSPs (HSP60, HSP70, and HSP90) are fundamental to cell survival, and mutation or deletion of the major HSP which is often lethal to both cells and organisms. In addition, HSP70 plays important cellular roles in protein synthesis and modifying processes, and can combine with many kinds of antigenic peptides to form antigen peptide-HSP compounds  . Furthermore, several studies have shown the ability of HSP70 to target vaccine antigens to antigen-presenting cells (APCs), including dendritic cells and macrophages, increasing vaccine immunogenicity ,, . Some HSPs were implicated in immune pathology and clinical manifestations of a variety of autoimmune diseases and/or metabolic disorders such as atherosclerosis  , diabetes  , systemic lupus erythematosus  , and Behcet's disease  . The role of some HSPs in antigen cross-presentation  and cancer immunotherapy  has also been reported. In addition, these proteins are initiators of immune response as well as targets of autoimmune attack. That is Microbial HSPs may stimulate cellular or humoral immune responses that might be cross-reactive with the corresponding self-HSPs or other self-antigens, leading to the induction of autoimmunity  .
HSPs are also known to play critical roles in innate immunity as well as adaptive immunity. They are capable of: (a) Activating specific toll-like receptors (TLRs), (b) Inducing the maturation as well as influencing the activation of APCs, (c) Providing polypeptides for specific triggering of the acquired immune response, and (d) Playing a major role in cross-presentation of extracellular antigens (e.g. microbial antigens) in parenchymal cells by the class I pathway, resulting in the induction of CD8+cytotoxic T-lymphocyte responses ,.
Besides, HSPs may facilitate the regulation of effector responses under appropriate conditions, which could be achieved by increasing the production of anti-inflammatory cytokines so as to deviate the cytokine balance from a proinflammatory type to an anti-inflammatory type  . HSPs may induce different types of regulatory T cells, including CD4 + Tr1 cells that secrete interleukin-10 (IL-10), and CD4 + CD25 + , and the transcription factor Forkhead-box-P3 (Foxp3)-expressing Treg that produce transforming growth factor-β (TGF-β) and IL-10 ,, .
It was shown that ATPase activity is essentially associated with the functions of the major HSP families. In addition to ADP/ATP, the peptide binding of the HSP90 system is under the control of calcium levels that induces the required conformational changes for peptide binding  . However, it was argued that HSPs constitute a third functional group of adjuvants  as they were recognized as major immunogens against pathogens  . It was shown that apart from acting as immunogenic antigens themselves, HSPs can also act as adjuvants to stimulate the immunogenicity of heterologous polypeptides to which they are either covalently or noncovalently coupled  .
The interactions between HSPs and parasitic diseases were reviewed in three articles. Shonhai et al.  focused on intracellular protozoan parasites such as Leishmania spp., Tryapnosoma cruzi, Plasmodium falciparum, and Toxoplasma gondii, and reviewed the role played by HSP90 in the development and growth of all of these intracellular parasites, as well as the biological functions of HSP70-HSP40 interactions. A year later, two review articles were published by Indian scientists focusing on HSP90. The potential importance of HSP90 in the growth and pathogenesis of several parasites such as Giardia, Plasmodium, Trypanosoma, and Leishmania was pointed out , . Thus, according to their view, several HSP90 inhibitors are expected to be promising targets as new drugs and candidate vaccines.
The objectives of the current review are to: (a) Summarize the functional properties of HSPs and their role in innate and acquired immune responses, (b) Shed light on their role in the pathogenesis and survival of the majority of parasites, (c) Review the literature for new drug discovery (HSPs-specific inhibitors) and vaccine candidates for parasitic diseases, and (d) Present other considerable uses of these biomarkers in parasitic diseases.
Functional properties of heat-shock proteins
The highly conserved HSPs molecules are defined as molecular chaperones. Their main function is the correction of the folding or functional conformation of cell proteins (under stress). This correction improves the capability of the cell proteins to: (a) Achieve their native form, (b) Be directed to the functional location (e.g. endoplasmic reticulum or mitochondria), (c) Resist denaturing, and (d) Regain their natural status on the occurrence of partial denaturation.
In other words, HSPs play important roles in assembly of protein complexes and translocation of proteins across cellular compartments, as well as in several immunological processes  .
In the old literature, it was believed that HSPs were 'danger-associated molecular patterns' because of being exclusively intracellular proteins only released on cellular injury or necrosis  . Now, it is apparent that HSPs are released from cells undergoing necrotic lysis in response to cytotoxic lymphocyte or natural killer action, or viral infections. Thus, especially members of HSP60, HSP70, and HSP90 families are capable of activating the innate immune response  . These members were shown to stimulate the human monocyte cell line (THP-1) to produce tumor necrosis factor (TNF-α), IL-6, and IL-8  . This stimulation was mediated through different cellular receptors, either by TLR-4 (for HSP60), or CD14 (for HSP65), or by interacting with both TLR2 and 4, in a CD14-dependent manner (for HSP70)  . Another factor in the innate immunity role is the different abilities of HSP70s to stimulate cells of the innate immune system cells. It was found that this ability is dependent on the HSP source, whether mammalian or microbial, i.e. mycobacterial HSP70 stimulates the innate immune response, whereas some members of mammalian HSP70 may downregulate the immune response instead , .
Cancer studies on sarcomas indicated that HSPs could modulate the generation of adaptive immunity, and the investigators identified gp96 (a member of the HSP90 family) as the tumor rejection antigen. Immunization with gp96 elicited sarcoma-specific immunity, whereas gp96 purified from other chemically induced tumors did not elicit immunoprotection  . It was proposed that the immunogenicity was conferred by tumor-specific peptides associated with the HSP90  , and this peptide binding is ATP/ADP dependent  . Interestingly, the uptake of HSP-chaperoned peptides by APCs is characterized by its availability for cross-presentation, which is the ability of exogenous antigens to enter the endogenous loading pathway of major histocompatibility complex (MHC) class I to produce CD8 + T cells  . The cross-presentation can occur either by the classical or the nonclassical MHC I loading, that is the vacuolar/endocytic or the cytosolic pathway  .
Heat-shock protein cancer vaccines
From preclinical to clinical trials (phase III), host gp96 purified from surgically removed tumors were utilized as cancer vaccines  . The clinical trials included tumors such as metastatic colorectal carcinoma, metastatic melanoma, non-Hodgkin lymphoma, pancreatic adenocarcinoma, and renal cell carcinoma  . The outcome of these clinical trials was variable, from statistically non-significant results in renal cell carcinoma, to a delay in disease progression compared with a group that received conventional chemotherapy and/or surgery in stage IV melanoma  . However, Colaco  reported that the majority of oncology animal studies used HSP70 instead of gp96.
Heat-shock proteins as infectious disease vaccines
Twenty years ago, a group of investigators found that recombinant mycobacterial HSP65 could activate murine macrophages in vivo, with intracellular inhibition of Listeria monocytogenes, but without protection against this pathogen  . Several studies were carried out to achieve protection in animal models using CD4 + and CD8 + T cells specific to HSP65  and DNA plasmids encoding Mycobacterium leprae HSP65  and HSP70  . However, these studies yielded variable outcomes that were attributed to a general, rather than specific stimulation of inflammatory responses  . Recently, the native mycobacterial HSP16 administered with the adjuvant dioctadecyl ammonium bromide elicited protection in a TB mouse model and was capable of boosting an existing BCG vaccination  .
Heat-shock protein and apoptosis
In intracellular protozoons, apoptosis is considered a defense mechanism because apoptotic-infected cells are phagocytized by macrophages with parasite elimination. This phagocytosis is initiated by cellular signaling pathways, and the intracellular parasites prevent these pathways to ensure their survival in the infected cell  . In their study, the investigators showed that HSPs expression is directed against the parasite infection and could interfere with apoptosis by activation of the factors responsible for the regulation of anti-apoptotic molecules.
Heat-shock proteins and helminths
Vaccination: In the early 1990s, HSP70 was one of the antigens considered important candidates for the anti-schistosomiasis vaccine with paramyosin, triosephosphate isomerase (TPI), glutathione-S-transferase (GST), and the membrane protein Sm23 , . Chinese investigators reported that water buffalo immunized with DNA vaccines of Schistosoma japonicum triosephosphate isomerase (SjCTPI) combined with the HSP70 plasmid and IL-12 resulted in protective immunity against schistosomiasis japonicum, with a variable reduction in all parameters (worm burden, fecal egg count, miracidial hatching rate, and hepatic egg counts)  . Two years later, two randomized double-blind control vaccine trials were conducted to determine the efficacy levels of the DNA vaccines encoding tetraspanin 23 kDa integral membrane protein (SjC23) or SjCTPI on their own, or when fused together with the dendritic cell targeting HSP70. They found that both vaccines incorporating HSP70 were more immunogenic and efficacious, as determined by the effect on egg burden  .
During 2010-2012, three Chinese articles were published on schistosomiasis vaccines. In one study, the molecular and functional characterization of S. japonicum SjMLP/HSP70 was reported. The molecule's sequence shared 77% identity with human HSP70 [mortalin-like protein (MLP)], and it was expressed widely in most developmental stages of S. japonicum (eggs, cercariae, schistosomula, and adult worms). The purified recombinant protein (rSjMLP/HSP70) was recognized by sera of infected mice. The investigators also found that the SjGST-DNA vaccine combined with SjMLP/HSP70 showed low grades of reduction (30 and 60%) of worm and egg burden in immunized mice, respectively  . In another study, the Chinese scientists identified in the sera of Microtus fortis, a naturally resistant vertebrate host of S. japonicum, substances with antischistosomal effects. They cloned and identified a 331 bp that was the HSP90a homologue (Mf-HSP90a). The cloned molecule showed antischistosomal effects (40-60% reduction in worm and egg burdens) both in vitro and in vivo  . In the third study, significant immunoprotective effects were observed when water buffalos were vaccinated with S. japonicum 23 kD membrane protein-HSP70 (SjC23-Hsp70) plus an IL-12 adjuvant. The investigators observed a reduction in all the parameters evaluated (female estrogen, fecal and hepatic egg burden)  .
Serodiagnosis: Four isolated HSP70 clones were evaluated for antibody activity against a panel of sera from baboons with acute and chronic schistosomiasis. The insert sizes of the four selected clones varied from 1150 to 2006 bp. It was found that antibody reactivity varied with clone length; the longest clone was the most reactive. Results suggested HSP70 immunodominance in acute as well as chronic schistosomiasis. The investigators recommended its use in the serological diagnosis of schistosomiasis mansoni  . Similar results were obtained on using molecules of soluble egg antigen in the diagnosis of schistosomiasis japonicum, where sera of mice with early schistosomiasis reacted with two protein molecules in soluble egg antigen: the HSP70 and 78 kDa glucose-regulated protein (Grp78/Bip)  . In a preliminary report, Brazilian investigators also proposed a strategy for the selection of cDNA clones that could be used in the diagnosis of schistosomiasis. Two out of five cDNA clones were identified as homologous to HSP70  .
Immune response: The mechanism(s) responsible for suppression of host immune responses in chronic schistosomiasis was investigated by studying the induction of CD4 + CD25 + T cells by HSP60 of S. japonicum (SjHSP60-derived peptide; Sj MHE1). The investigators found that all mice immunized with Sj MHE1 or lymphocytes from in vitro Sj MHE1-pretreated naive mice showed an increase in CD4 + CD25 + T-cell populations as well as IL-10 and TGF-β release. The investigators suggested the possible role of TLR2 on CD4 + CD25 + induction caused by HSP60  . HSP70, HSP90, and HSP97 were detected as major constituents of the proteomics profile of the excretory/secretory (E/S) products of adult S. japonicum. The investigators emphasized their central roles in immunomodulation for the host-parasite relationship  . In addition, Chinese scientists succeeded in cloning and constructing the recombinant plasmid of the S. japonicum HSP40 gene, which significantly initiated macrophage activation  .
Cancer bladder: In 2008, an Egyptian study clarified the significant association between HSP27 and HSP70 and cancer bladder caused by schistosomiasis. The investigators detected both HSPs in 60 and 68% of their patients, respectively. In addition, they found a significant correlation between HSPs expression and tumor grade and stage as well as its recurrence. They concluded that both HSPs expressions could be used as predictive biological markers for disease progression  .
Parasite development: Besides the morphological changes in cercaria-schistosomula transformation, cercariae have to modulate the temperature change (from external water to body temperature) and osmolarity change (from hypotonic water to saline bloodstream osmolarity). To overcome both challenges, the acetabular glands secrete HSPs as shown from the proteomic analysis of secretory products involved in host skin invasion by cercariae  . S. mansoni HSP70, HSP86, and HSP60 were detected in S. mansoni cercariae  , whereas HSP90 is a phosphoprotein detected in the different developmental stages and both sexes of S. japonicum  . One year later, another group of Chinese investigators emphasized the critical role of HSP in parasite development  . However, the heat-shock response pathway is a highly conserved and adaptive response system, and heat-shock factor 1 (Hsf1) is a major regulator of its pathway  . Hence, the role of gene encoding schistosomes Hsf1 in cercaria-schistosomula transformation was investigated. The results obtained confirmed the existence of Hsf1 in the cercarial stage and its expression in different schistosomal stages. The investigators identified antibodies against Hsf1 labeled on cercarial acetabular glands  .
E. granulosus : HSP70 was first reported in the serodiagnosis of hydatid cyst (HC) in 1997 in comparison with human HSP70. Both HSPs70 were assessed against patients' sera and controls. Specific antibodies' reactivity against human and parasite HSP70 was detected in 10% and 60% of the infected sera, respectively. However, 21% of the control sera reacted with E. granulosus HSP70, but the reactivity level was significantly higher in the infected patients  . Later, E. granulosus HSP70 was reported to stimulate the humoral and cell-mediated immune responses. Using immunoblotting, IgG, IgG4, and IgE specific to Eg2HSP70 as well as increased levels of TNF-α, interferon-g (IFN-g), IL-4, and IL-10 were detected in the sera of infected patients  . In addition, proteomic analysis of protoscoleces and hydatid fluid extracted from HC identified HSP20 and HSP70  .
In 2010, HSP20 was identified and characterized as an immunogenic protein of E. multilocularis, and its recombinant variant showed specific reactivity to sera from infected dogs, suggesting its efficacy as a vaccine candidate  . One year later, also using the proteomic approach, Italian investigators succeeded in identifying HSP20 as a biological marker for the development and progression of HC. HSP20 could react with sera from HC-infected patients with different disease phases. The reaction was higher with sera from patients with active disease than in sera from patients with inactive disease  . Moreover, fluids from fertile HCs collected from sheep and humans as well as from infertile HCs from cattle were analyzed using tandem mass spectrometry. The investigators identified 48 proteins of parasitic origin, of which parasitic HSPs, cathepsin B and Annexin A13, were detected exclusively in infertile cysts. The investigators reported increased cellular stress and apoptosis as the major causes of their infertility  .
HSPs play a critical role in the parasite's successful establishment, its survival under stressful conditions, and its reproduction in an adverse habitat  . In 2009, HSB10 was characterized in Strongyloides ratti parasitic female E/S products  . A proteomic study of S. ratti was carried out to identify proteins found as E/S products from different developmental stages (infective larvae, parasitic females, and free-living stages). Small HSP (SrHSP10) and SrHSP60 were among the proteins abundantly observed in all the stages  . In the same year, another team of German investigators used mass spectrometry to identify and characterize two novel HSPs from S. ratti (SrHSP-17.1 and SrHSP-17.2) in the parasitic female E/S products. In their report, they reported the Sra-HSP-17s genomic organization, recombinant expression, purification, and antigenicity. They also showed that Sra-HSP-17s activated host cells (monocytes, macrophages, and intestinal epithelial cells), but not the lymphocytes and granulocytes. Moreover, purified rSrHSP-17s could induce IL-10 production by mononuclear cells  . Nouir et al.  from Germany worked on strongyloidiasis by analyzing the immune response to S. ratti HSP60 (SrHSP60) in infected mice. Their results showed that SrHSP60 induced Th1 response in vivo, whereas alum-precipitated srHSP60 induced Th2 response and partial protection against the challenge infection  . In the same year, they generated monoclonal IgM specific for srHSP60, which was used as a vaccine candidate in a mice model. Results showed a reduction in the number of the parasitic adults and migrating larvae in intestinal and disseminated strongyloidiasis  .
Levels of HSPs were used to measure stress tissue injuries caused by T. spiralis. Spanish investigators assessed HSP25, HSP60, HSP70, and HSP90 kinetics production from injured liver and muscle of infected and control mice. They found that HSP25 and HSP60 production was observed in the affected liver and infected muscles  . In the same year, the same investigators reported that HSP25, HSP60, and HSP70 production increased and varied in infected rat tissues (brain and spleen) according to the infection cycle, whereas a significant reduction in HSP90 was observed. The investigators did not suggest a role for HSP90 in the infection cycle  . However, no difference was detected in any of these HSPs in tissues of infected rats (muscle, liver, brain, and spleen) with primary trichinosis and rats reinfected 45 days after the primary infection  . One year later, the same investigators measured these HSPs in other infected organs (intestines, mesenteric lymph nodes, heart, and lungs) at different time points during first exposure and second reinfection. The results suggested that in reinfection, there is a sort of challenge and muscle larvae developed to adults, producing newborn larvae that were trapped in the mesenteric lymph nodes, thus increasing HSPs levels  . In another study, Martinez et al.  used three techniques to identify and purify HSPs (60, 70, and 90) from T. spiralis larvae: affinity chromatography, immunoblotting using either their monoclonal antibodies or preimmune and immune rat sera, and ELISA. Only sera from infected rats (7 days after infection) showed reactivity against the HSPs identified  .
A team of Egyptian scientists succeeded in obtaining HSP70 from crude somatic extracts and E/S products of adult T. spiralis, and used them to immunize mice against challenge infection. The resulting strong immunogenic reactions of HSP70 were evaluated by parasitological measures (worm and muscle larval burden) and increased total g-globulins  . The first molecular cloning and characterization of HSP70 from T. spiralis was performed in China. The recombinant TsHSP70 formulated with Freund's adjuvant proved to be a possible candidate vaccine against trichinosis as shown in the strong humoral immune responses in mice challenged with T. spiralis larvae  . Two years later, screening of cDNA libraries from T. spiralis adult worms against sera from infected pigs produced several positive clones. Of these clones, 14 showed sequence identity with HSP70, suggesting its major role in host-parasite interactions  .
In lymphatic filariasis, there is impaired monocyte functions indicated by reduced production of chemokines (e.g. IL-8, eotaxin, and Exodus II), and cytokines (e.g. IL-1α, IL-12p40, IL-12p70, IFN-g, and IL-10)  . A group of American scientists assessed gene expression patterns of monocytes from infected patients and healthy individuals. They recorded differences in expression among the genes involved in apoptosis and cell adhesion. They further compared these gene expressions to before and after treatment (single dose of ivermectin-albendazole), and the most detected alterations were found in the expression of HSP60, HSP70, HSP90, and HSP105 genes. The investigators concluded that treatment resulted in the clearance of the parasite's antigens that retained monocyte-suppressive functions, releasing chemokines and cytokines as well as increasing HSPs expression  . However, it was reported that recombinant Wolbachia (microfilarial symbiotic bacteria) HSP60 (rwmHSP60) regulates immune activation in lymphatic filariasis by inhibition of secretion of proinflammatory cytokines from activated T cells through TLR signaling. Decreased CD69 with elevated CD127 and CD62L as well as IL-10 and TGF-β in infected patients confirmed reduced T-cell activation because of HSP60 stimulation  . One year later, Indian investigators reported that rwmHSP60 also induced proinflammatory cytokine production (IL-1β, IL-6, and TNF-α), reduced phagocytic function of monocyte/macrophage, and promoted apoptosis of human monocytes  .
Wuchereria bancrofti and Brugia spp.: Brugia spp. (malayi and pahangi) HSP70 was first discovered in 1987, and was described as a protein expressed in both the insect and host parasitic stages. The investigators reported that it played no role in host immune response  . At the same time, they used the C-terminal portion of Brugia spp. HSP70 (Bpa-26) as an indicator for chronic Brugian filariasis. The investigators found significantly higher IgG3 levels in chronic patients compared with microfilaremic and asymptomatic amicrofilaremic patients  . The recombinant protein of Brugia malayi Wolbachia HSP60 was also reported to generate antibody response (total IgG and Ig1) in all individuals from an area endemic for W. bancrofti  . In 2010, HSP70 identified from the bovine filarial parasite Setaria cervi showed 98% identity with that of W. bancrofti and only 28% with human HSP70  .
The specific inhibitor of B. pahangi HSP90 such as geldanamycin was reported to kill adult worms and microfilariae in vitro. However, it proved to have severe hepatotoxic hazards besides being metabolically and chemically unstable  . One year later, the same investigators developed a fluorescence polarization assay that proved sensitive and specific in identifying new compounds that bind to the HSP90 pocket and could be used as an HSP90 specific inhibitor. The investigators validated their assay and its adaptation to screen HSP90 inhibitors against other parasites  . In a study carried out by American and Indian investigators, the vaccine potential of B. malayi HSP12.6 (BmHSP12.6) was evaluated in infected mice. The results showed that vaccinated mice had ~72% protection against the challenge infection. The investigators suggested that BmHSP12.6 had host immunomodulatory functions that might interfere with microfilaria establishment in the host. Moreover, there was a significant increase in IgG1 and IgG2a antibody responses. They concluded that BmHSP12.6 could be developed into a vaccine candidate against B. malayi  . One year later, BmHSP12.6 was used as a partner in a trivalent fusion vaccine, and conferred significant prophylactic protection (95%) against challenge infection  . Recently, B. malayi HSP12.6 (which is an a crystalline domain and c-terminal extension) was included in a vaccine with a B. malayi abundant larval transcript (rBmALT-2) and a B. malayi tetraspanin large extracellular loop (rBmTSP LEL) to form rBmHATαc  . It conferred 68% protection in mice with challenge infection that increased to more than 95% protection when AL007 (alum from IDRI) or AL019 (alum plus TLR-4 agonist from IDRI) was used as an adjuvant  . More recently, German scientists investigated the role of B. malayi HSP70 in immunizing BALB/c mice against challenge infection with Litomosoides sigmodontis (rodent filarial worm). The results indicated reduced numbers of pleural cavity larvae and circulating microfilariae as well as increased production of type I and II cytokines. The investigators concluded its potential role as a vaccine candidate  .
Onchocerca volvulus: HSP70 was first reported in 1989 when investigators recognized three cloned filarial immunogenic antigens that reacted with sera from infected patients. One of these immunogenic antigens recognized by amicrofilaremic patients is an O. volvulus protein homologous to the 70 kDa HSP of the African frog Xenopus laevis  . Later, chaperonin 60 (CPN60) or HSP60 of O. volvulus (OvCPN60) was reported in 2000 and the investigators detected it in all life-cycle stages. Antibodies raised against OvCPN60 were found in ~90% of infected patients in West Africa  . In 2008, a group of German scientists reported that killing Wolbachia bacteria in O. volvulus-infected patients resulted in an increase in HSP60 production from filarial mitochondria. To differentiate between HSP60 from Wolbachia and that of filarial mitochondria, they used antiserum raised against HSP60 to specifically bind to the protein and stain it in both Wolbachia and mitochondria. They attributed this increased expression to homeostasis disruption of endosymbiosis  .
Taenia solium: A small HSP, Tsol-sfISP35.6, was isolated by antibody screening of a T. solium cDNA library, followed by cloning. Using western blot analysis and ELISA, the clone reacted with 80% of sera of infected pigs, 84% of patients with active neurocysticercosis, and 71% of patients with inactive diseases  .
Echinostoma spp.: Using a proteomic approach, Spanish investigators identified protein spots corresponding to 10 proteins including HSP70 in E. friedi E/S products. The stress protein showed variable expression patterns in chronic and acute infections in experimentally infected rodents, suggesting its role in parasite survival  . HSP70 was also identified in E. caproni E/S products. Another group of Spanish investigators recognized an early IgM response generated by HSP70, suggesting its importance in parasite establishment because of its early exposure to the host immune response. Moreover, IgA response was mediated by HSP70, which was attributed to its close contact with the host mucosal surface  .
Paragonimus westermani: In 2007, the P. westermani egg antigen gene was cloned and evaluated as an antigen for the serological diagnosis of paragonimiasis. Using ELISA against sera from patients infected with different parasites (including patients with paragonimiasis) and negative controls, its sensitivity and specificity were 90.2 and 100%, respectively. Moreover, its sequence was 40, 38, and 35% identical to HSPs from S. japonicum, S. mansoni, and T. saginata, respectively  .
Fasciola spp.: In 2008, F. hepatica and F. gigantica HSP70s were cloned and characterized. Using Western blot analysis, Australian investigators found 98-99% identity in their protein sequences. However, the 70 kD protein was not detected in the parasite E/S products. Analysis of HSP70 expression in fascioliasisaffecting sheep (not cattle), showed higher HSP70 expression in F. gigantica than F. hepatica. This result highlighted the importance of HSP70 as a biochemical marker of F. gigantica stress response  .
Clonorchis sinensis: In clonorchiasis, HSP27, HSP90 expressions as well as levels of inflammatory cytokines (IL-1β, IL-2, TGF-β2, and IFN-α1) were increased in infected hamsters compared to control group. This significant increase was correlated with the severity of bile duct hyperplasia, liver fibrosis, and hepatic necrosis  .
HSPs play important roles in the correction of cell protein functions under stress conditions and share in several immunological processes of innate and adaptive immunity. Their role in the vaccination era was reported against cancer (such as cancer colon, renal cell carcinoma, and pancreatic adenocarcinoma) as well as against microbial and parasitic diseases. HSPs expression was also found to be directed against apoptosis, especially in intracellular protozoon.Several studies were carried out using HSP70 as a vaccine candidate in schistosomiasis japonicum. In addition, few studies suggested the use of HSP70 in the serological diagnosis of schistosomiasis mansoni.HSP70 and HSP90 were detected as major constituents of the proteomics profile of the E/S products of adult S. japonicum, and they were impacted in host-parasite relationship immunomodulation. However, HSP70, HSP86, and HSP60 were detected in the secretory products of S. mansoni cercariae, and they play a critical role in parasite development.In hydatid disease, E. granulosus HSP70 was observed as an immunogenic protein stimulating both the humoral and the cell-mediated immune responses. Use of E. multilocularis HSP20 was suggested as a vaccine candidate.In strongyloidiasis, small HSP (HSP10) and HSP60 were observed in all the stages of S. ratti. Other sHSPs (HSP17) were detected in the parasitic female E/S products, which activated most host cells and induced IL-10. However, HSP70 was found to induce Th1 response in vivo, suggesting its use in protection against challenge infection.Several HSPs were reported to be increased during stress tissue injuries in trichinosis such as HSP25, HSP60, and HSP70. There is some contradiction on HSP90 production from the injured tissues. However, HSPs 60, 70, and 90 from T. spiralis larvae showed reactivity against sera from T. spiralis-infected rats.T. spiralis HSP70 produced strong immunogenic reactions when used to immunize mice against challenge infection.HSP70 of both W. bancrofti and Brugia spp. were recognized as immunogenic proteins capable of significant production of IgG3 levels. In addition, B. malayi HSP70 was used to immunize mice and showed its potential role as a vaccine candidate. However, B. malayi HSP12.6 was used as a partner in a trivalent fusion vaccine (rBmHATαc), which conferred excellent protection in mice if used with AL007 or AL019 as adjuvants.Few other studies have focused on HSPs in other diseases caused by helminths, for example O. volvulus, in which HSP60 was detected in all life-cycle stages. A clone of HSP 35.6 in T. solium reacted with the majority of sera from patients with active neurocysticercosis. HSP70 was detected in different Echinostoma spp., and it was found that IgA response was mediated by HSP70. In fascioliasis, HSP70 showed high potentiality as a biochemical marker in infection with F. gigantica. In clonorchiasis, HSP27 and HSP90 expressions were elevated with increased production of inflammatory cytokines.
Conflicts of interest
There are no conflicts of interest.
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