Cross-reaction of antigen preparations from adult and larval stages of the parasite Setaria equina with sera from infected humans with Wuchereria bancrofti

Crude antigenic preparations from Setaria equina were used in ELISA and Western blotting to examine cross-reaction with human sera from areas endemic for bancroftian filariasis. Sera from normal subjects from non-endemic areas were included as negative controls. Cross-reaction was found between S. equina antigens and antibodies in the sera of Wuchereria bancrofti-infected patients, with the highest levels observed between sera of chronic infected patients and Setaria spp. crude female worm surface antigen (CFSWA). In the absence of active transmission of Setaria spp. infection, CFWSA is useful to detect chronic W. bancrofti infection before patients become symptomatic, particularly when chronic patients are known to be amicrofilaraemic. In the presence of active S. equina infection, antigens from the adult and microfilaraemic stages showed the highest degree of cross-reaction with human sera.

Adult 175 kDa collagenase antigen ofSetaria cerviin immunoprophylaxis againstBrugia malayiin jirds

A 175 kDa antigen fraction with collagenase activity was isolated and purified from somatic extracts of adultSetaria cervifemales using column chromatography involving consecutive steps of DEAE-Sepharose CL6B and Sephadex G-100. The optimum pH for 175 kDa collagenase was found to be pH 7.0. Sensitivities to a variety of inhibitors and activators indicated that the 175 kDa coIlagenolytic enzyme was metalloserine in nature. The enzyme hydrolysed a variety of protein substrates such as haemoglobin, casein, azocasein (general substrates) and collagen, FALGPA (furanoyl-acryloyl-leu-gly-pro-ala), the specific substrate of collagenase. The enzyme showed 57% inhibition by jird anti-somatic collagenase antibodies and reacted insignificantly with normal jird sera. Further analysis was undertaken on the immunoprophylactic potential of 175 kDa collagenase in inducing immunity againstBrugia malayi(a human filarial parasite) in jirds (Meriones unguiculatus)in vitroandin situ. Immune sera of jirds raised against this antigen promoted partial adherence of peritoneal exudate cells toB. malayimicrofilariae (mf) and infective larvae (L3)in vitroand induced partial cytotoxicity to the parasites within 48 h. The anti-S. cervi175 kDa antigen serum was more effective in inducing cytotoxicity toB. malayiL3, than mf. In the microchambers implanted inside immune jirds, host cells could migrate and adhere to the mf and infective larvae thereby killing them partially within 48 h.

Setaria digitata secreted filarial lipids modulate IL-12 signaling through JAK-STAT pathway leading to the development of Th1 response

Filariasis is a debilitating parasitic disease in many tropical countries. Despite the highly evolved immune system, the filarial parasites successfully evade host immunity to persist for a sustained period of time. Earlier studies have shown that the filarial parasites achieve this long-term survival through release of immunosuppressive materials in the host. In this study, we show that the secreted filarial lipids (SFL) isolated from Setaria digitata suppress Th1 immune response. While immunization with myelin antigen induces Th1 response in mice, in vitro treatment with SFL resulted in a dose-dependent decrease in myelin antigen-induced proliferation and secretion of IL-12 and IFNgamma. The SFL also inhibited IL-12-induced T cell proliferation and Th1 differentiation in vitro. The inhibition of T cell responses by SFL associates with the blockade of IL-12-induced activation of JAK-STAT signaling pathway in T cells. These findings suggest that the SFL modulates Th1 immune response by blocking IL-12 signaling in T cells and thus play a role in host immune evasion of filarial parasites.

Setaria digitata: identification and characterization of a hypodermally expressed SXP/RAL2 protein

SXP-1, an immunodominant filarial protein identified from Wuchereria bancrofti from our centre and previously exploited for diagnosis of human lymphatic filariasis, has been shown to be well conserved across several filarial species. In the present study, we describe the identification of SXP protein from the cattle filarid Setaria digitata using antiserum raised against recombinant WbSXP-1, and were able to detect 34 and 66kDa proteins from the crude protein extracts of S. digitata. These reactive proteins were found to be sheath proteins localized to the hypodermal region of the parasite.

Setaria cervi: immunoprophylactic potential of glutathione-S-transferase against filarial parasite Brugia malayi

Glutathione-S-transferase (GST) has been detected in the adult female Setaria cervi, a bovine filarial parasite. The role of S. cervi GST antigen in inducing immunity in the host against Brugia malayi microfilariae and infective larvae was studied by in vitro antibody dependent cell mediated reaction as well as in situ inoculation of filarial parasites within a microchamber in Mastomys. The immune sera from glutathione-S-transferase immunized Mastomys promoted the adherence of peritoneal exudate cells to B. malayi microfilariae and infective larvae in vitro inducing 80.7 and 77.6% cytotoxicity, respectively in 72 h. In the microchambers implanted in the immunized Mastomys host cells could migrate and adhere to the microfilariae and infective larvae and induced 77.8 and 75% cytotoxicity to B. malayi microfilariae and infective larvae in 72 h, respectively. These results suggest that native GST from S. cervi is effective in inducing protection against heterologous B. malayi filarial parasite and thus has potential in immunoprophylaxis.

Deficiency of antibody responses to T-independent antigens in gerbils---Meriones unguiculatus

Meriones unguiculatus commonly known as gerbils are widely used as animal models for a variety of parasitic infections such as Brugia malayi, Entamoeba histolytica, Giardia duodenalis, Toxoplasma gondi, Helicobacter pylori, Strongyloides stercoralis and Echinococcus multilocularis. Groups of BALB/c mice, gerbils and XID mice were studied for antibody responses to T-independent antigens. Gerbils were found to be significantly deficient in eliciting antibodies to both dextran and phosphorylcholine (PC) in comparison to BALB/c mice. The antibody response of gerbils to T-independent antigens was found to be similar to the response observed in Bruton's tyrosine kinase (Btk) deficient XID mice, which are known to be poor responders to T-independent antigens. Similar to XID mice, normal gerbil sera were found to be deficient in naturally occurring antibodies to single stranded DNA (SS-DNA), lipopolysaccharide (LPS) and phospholipids. This raises the possibility of a deficiency of CD5+ B-lymphocytes (also known as B-1 cells) in gerbils, since deficiency of this sub-population of B-lymphocytes has been attributed to the absence of such naturally occurring antibodies in XID mice. These results indicate the need to study immunogenicity of parasite T-independent antigens and their relationship to protective immunity in parasitic infections in gerbils.

Human bancroftian filariasis - a role for antibodies to parasite carbohydrates

Studies on immune responses to parasites have been undertaken in filariasis with a view to understand protective immunity, pathogenesis of the disease process and mechanisms of immune deviation. However none of the investigations conducted so far on antibody responses have addressed the issue of immunogenicity of filarial carbohydrate antigens in human lymphatic filariasis. In this communication we report details on relative protein and carbohydrate contents of various developmental stages of filarial parasites and antibody responses to filarial proteins (Fil.Pro) and carbohydrates (Fil.Cho) in different clinical spectrum of human bancroftian filariasis. As expected, antibodies of IgM and IgG2 subclass recognized primarily Fil.Cho while IgG4 filarial antibodies recognized exclusively Fil.Pro. Reactivity of IgG3 to Fil.Cho was similar to that of IgG2 while IgG1 more readily recognized Fil.Pro than Fil.Cho. The IgG2 and IgG3 antibodies to Fil.Cho were found to be significantly more in patients with chronic filarial disease and in endemic normals when compared with microfilariae (mf) carriers while IgG4 antibodies to Fil.Pro were significantly more in mf carriers. The dichotomy in reactivity of filarial IgG2, IgG3 and IgG4 was dependent on active filarial infection as indicated by presence of circulating filarial antigen (CFA). Individuals with CFA were found to possess significantly more IgG4 to Fil.Pro than those without CFA while IgG2 and IgG3 levels to Fil.Cho was significantly more in CFA negative subjects when compared to those with CFA. Although IgG1 reacted more readily with Fil.Pro, unlike IgG4, their levels were significantly more in CFA negative subjects when compared to those with active filarial infection. Absorption of sera with phosphorylcholine (PC) resulted in no significant loss of reactivity to Fil.Cho indicating that most of the anticarbohydrate antibodies were recognizing non-PC determinants in human filariasis. Elevated levels of IgG2 and IgG3 antibodies to Fil.Cho in individuals free of filarial infection indicate a possible role for carbohydrate antigens in induction of protective immunity in human filariasis.

Wuchereria bancrofti: detection of microfilariae in asymptomatic microfilaremic individuals with Setaria digitata antigens

A dot-ELISA for detection of microfilariae of Wuchereria bancrofti in an endemic area was developed. This test can differentiate the endemic normals from the microfilaraemic asymptomatic individuals. Antigens of molecular weight 130 and 52 kDa of the cattle filaria worm Setaria digitata were used for this test. It was observed that these two antigens were also present in the serum of asymptomatic microfilaraemic individuals.

Setaria digitata infections in cattle: parasite load, microfilaraemia status and relationship to immune response

A total of 110 cattle were examined in an area endemic for Bancroftian filariasis for the prevalence of infection of the bovine filarial parasite Setaria digitata. About 12.5% of cattle were found to harbour both adult worms in the peritoneum and microfilariae (mf) in circulation; 70% of the cattle were amicrofilaraemic but with an adult worm infection. A third group of cattle (16.5%) was free of detectable mf and adult worms. The presence of adult worms and/or mf did not influence the antibody levels to any of the four antigen preparations of S. digitata. However, there was a significant inverse relationship between the presence of antibodies to microfilarial sheaths and the absence of circulating mf as shown by the immunoperoxidase assay. Cattle immunoglobulin containing high titres of anti-sheath antibodies cleared circulating microfilariae very effectively in Mastomys coucha thus demonstrating the protective nature of anti-sheath antibodies in eliminating circulating microfilariae in vivo.

Phosphocholine-containing, zwitterionic glycosphingolipids of adult Onchocerca volvulus as highly conserved antigenic structures of parasitic nematodes

Human Onchocerca volvulus infection sera were found to recognize zwitterionic glycolipids of O. volvulus and to cross-react with those of other parasitic nematodes (Ascaris suum, Setaria digitata and Litomosoides sigmodontis). By the use of an epitope-specific monoclonal antibody, zwitterionic glycolipids of all these nematode species were observed to contain the antigenic determinant phosphocholine. A hyperimmune serum specific for arthro-series glycolipid structures reacted with the various neutral glycolipids of all these nematodes, which demonstrated that their oligosaccharide moieties belonged to the arthro-series of protostomial glycolipids. These results indicated that arthro-series glycosphingolipids carrying, in part, phosphocholine substituents, represent highly conserved, antigenic glycolipid markers of parasitic nematodes. Three glycolipid components of the O. volvulus zwitterionic fraction were structurally characterized by matrix-assisted laser-desorption/ionization time-of-flight MS, methylation analysis and exoglycosidase treatment. Their chemical structures were elucidated to be phosphocholine-6GlcNAc(beta1-3)Man(beta1-4)Glc(1-1)ceramide, GalNAc(beta1-4)[phosphocholine-6]GlcNAc(beta1-3)Man(beta1-4)Glc(1-1) ceramide and Gal(alpha1-3)GalNAc(beta1-4)[phosphocholine-6]GlcNAc(beta1-3)Man(beta 1-4)Glc(1-1)ceramide for the zwitterionic ceramide tri-, tetra- and penta-hexosides respectively. The ceramide composition was found to be dominated by 2-hydroxylated docosanoic (C(22h:0)), tricosanoic (C(23h:0)) and tetracosanoic (C(24h:0)) acids, and C(17) sphingosine (C(d17:1)) (where (h) is hydroxylated and (d) is dihydroxylated).

NF-kappaB is essential for induction of pro-inflammatory cytokine genes by filarial parasitic sheath proteins

The transcription factor NF-kappaB plays critical roles in immune and inflammatory responses. Here we show that filarial parasitic sheath proteins cause activation of NF-kappaB in the airway epithelial HEp-2 cell line. This activation was transient and saturable, and involved degradation of the cytoplasmic inhibitor protein IkappaBalpha. Stable expression of IkappaBalpha mutated at Ser32 and Ser36 to Ala caused inhibition of NF-kappaB activation, indicating that this activation involves the IkappaB kinase-mediated pathway. Moreover, while it did not influence the HEp-2 cell survival, selective blockade of NF-kappaB activation resulted in inhibition of the expression and the secretion of pro-inflammatory cytokines, tumor necrosis factor-alpha, interleukin-6 and interleukin-8. Thus, initial transient activation of NF-kappaB resulted in profound and long-term effects on epithelial cell responses to filarial parasitic proteins. These findings implicate an important role for NF-kappaB in orchestrating inflammatory reactions associated with tropical pulmonary eosinophilia.

Apoptosis induced by filarial parasitic sheath protein in HEp 2 cell lines blocked by ectopic expression of bcl 2

Chronic filarial patients exhibit an occult manifestation, Tropical Pulmonary Eosinophilia, (TPE), caused by an exaggerated immune response to shed and circulating filarial antigens, leading to extensive lung damage. We have attempted to examine the disease in vitro using the human epithelial cell line, HEp2. Filarial sheath proteins induce apoptosis in HEp2 cells characterized by chromatin condensation, internucleosomal DNA cleavage, positive staining for TUNEL assay and shows a sub-G1 peak on FACS analysis. In order to understand subcellular events and to analyse the protective role of bcl2, we engineered HEp2 to overexpress Bcl2 protein. HEp2 bcl2 cells do not undergo apoptosis on exposure to filarial sheath protein, indicating that filarial protein-induced apoptosis in epithelial cells proceeds via a pathway, inhibitable by overexpression of bcl 2.

Proinflammatory cytokines secreted by monocytes of filarial patients

The levels of interleukin 1, granulocyte macrophage colony stimulating factor (GM-CSF) and tumour necrosis factor (TNF)-alpha secreted by the monocytes of filarial patients, such as asymptomatic microfilaremics (MF), chronic pathology (CP), and normal individuals, residing in a Wuchereria bancrofti endemic area (EN) in response to whole Brugia malayi antigen (BmA) and Setaria digitata (Sd-cuticular) and a recombinant filarial antigen (pRJ51) were studied. Stimulation of peripheral blood adherent cells with whole parasite antigen showed marked increase in IL-1 levels in MF as compared to CP or EN. The recombinant antigen stimulation, however, resulted in similar levels of IL-1 in MF and CP. In contrast, stimulation of peripheral blood adherent cells with whole parasite antigen produced high levels of GM-CSF and TNF-alpha in CP as opposed to MF or EN. Recombinant antigen stimulation, however, produced high levels of GM-CSF in EN as compared to MF or CP, while no significant change in the release of TNF-alpha was observed in these patients. These results suggest that monocytes from filarial patients exhibit functional activity similar to that observed by the monocytes of endemic normals (control group).

Characterization of secretory acetylcholinesterase from Setaria cervi microfilariae: a potential antigen for diagnosis of human filariasis

Acetylcholinesterase (AChE) is released to the external medium when microfilariae (m.f.) of Setaria cervi, a bovine filarial parasite, are maintained in vitro. Intense enzyme staining at amphids, excretory pores, anal vesicle and phasmids suggest an active secretion of AChE from m.f. Excretory-secretory products of m.f. displayed two electromorphic variants of AChE when resolved by 6% nondenaturing PAGE. The two isoforms of AChE (A and B) were separated on the basis of charge by DEAE sepharose CL 6B column following gel filtration. The two isoforms showed differing kinetic properties with respect to substrate specificity and inhibitor sensitivity. Anti-Nippostrongylus brasiliensis AChE antibodies cross-reacted with the affinity purified secretory AChE in ELISA. Immunoblotting of purified AChEs with cross-reacting anti-AChE antibodies revealed the presence of an approximately 75 kD protein in the isoenzyme A and an approximately 45 kD protein in B, whereas both proteins were present in the enzyme purified via affinity chromatography on edrophonium sepharose column.

Antibody response to a filarial antigen fraction in individuals exposed to Wuchereria bancrofti infection in India

An antigen fraction (DssdI) was isolated from the aqueous-insoluble components of adult Setaria digitata. Rabbit antiserum to DssdI labeled the sheaths of Wuchereria and Setaria microfilariae suggesting DssdI to be surface associated. Antibody responses to DssdI were determined in Wuchereria bancrofti exposed individuals. IgM titre was highest in endemic normals (EN; asymptomatic amicrofilaraemic) followed by chronic filarial patients (CP) and asymptomatic microfilaraemics (AS). IgG titer was high in both chronic filariasis and endemic normals. The microfilaraemic group had the lowest titer. The seropositivity rate in AS was 28% for IgG and 10% for IgM, in CP 100% for IgG and 33% for IgM, and in EN 86% for both antibodies. An age-dependency of IgM but not of IgG antibodies was observed in endemic normals, with IgM prevalence reaching a plateau by 12 years of age. The subclass composition of the antibody response to DssdI appeared to be primarily IgG3 in endemic normals, IgG1 in chronic filariasis and IgG4 in asymptomatic microfilaraemics. Diethylcarbamazine (DEC) treatment led to a significant increase in IgG and IgM levels in microfilaraemic individuals. Of interest, the expression of IgG subclasses altered. There was an increased IgG3 and IgG1 response associated with a reciprocal decrease in IgG4 following DEC therapy.

Immune response of electroeluted detergent soluble 29 kDa antigen from Setaria digitata (Von Linstow)

Filariasis is one of the typical parasitic infections which cause immune suppression during the course of infection in both humans and experimental animals. A 29 kDa protein isolated from detergent soluble antigen of S. digitata showed maximum inhibition of cell mediated immune response. The heat inactivated 29 kDa protein was found to be devoid of property of suppression of immune response in the host. Histological study of spleen of BALB/C mice immunized with 29 kDa protein showed changes in regions of spleen such as follicle, trabeculae, capsule, reticuloendothelial cells and eosinophils. The 29 kDa protein, the most reactive of the detergent soluble proteins produced partial suppression of immune response, thereby contributing to the factors responsible for the survival of filarial parasites in hosts.

Setaria digitata adult 14- to 20-kDa antigens induce differential Th1/Th2 cytokine responses in the lymphocytes of endemic normals and asymptomatic microfilariae carriers in bancroftian filariasis

High titers of parasite antigen-specific IgG4 antibodies have been found to be circulating in the peripheral blood of chronic patients, asymptomatic microfilariae carriers, and endemic normals in bancroftian filariasis. But in contrast to this, the titers of antigen-specific IgG1, IgG2, and IgG3 isotype antibodies are much lower. Using soluble antigens of adult Setaria digitata, a cattle parasite which shows strong antigenic reactivity with filaria sera, we have identified, by immunoblot, 14- to 20-kDa antigens which are recognized only by the IgG4 isotype antibodies present in the sera of asymptomatic microfilariae carriers. These 14- to 20-kDa antigens, after fractionation by SDS-PAGE and transfer to nitrocellulose paper, when solubilized and tested in vitro, induced secretion of a higher quantity of IFN-gamma and a lower quantity of IL-4, IL-5, and IL-10 (differential Th1 and Th2 response) in the lymphocytes of endemic normals in comparison to what they induced in the lymphocytes of asymptomatic microfilariae carriers.

Secretory acetylcholinesterase of Setaria cervi microfilariae and its antigenic cross-reactivity with Wuchereria bancrofti

Setaria cervi, a bovine filarial parasite, secretes acetylcholinesterase during in vitro cultivation. A significant amount of enzyme activity was detected both in culture media and somatic extracts of different developmental stages of the parasite. The microfilarial stage showed a higher level of AChE activity than adult worms, with females being considerably more active than males. The secretory enzyme from microfilariae preferentially utilized acetylthiocholine iodide as substrate and showed two electrophoretically distinct isoforms in native PAGE. Secretory enzyme was purified from the excretory/secretory products of microfilariae using edrophonium chloride linked to epoxy-activated sepharose. Analysis of purified acetylcholinesterase by SDS-PAGE revealed the existence of two proteins of 75kD and 45kD under nonreducing conditions. These secretory enzymes are antigenic and cross-reactive with Wuchereria bancrofti-infected asymptomatic microfilaraemic human sera when tested by enzyme linked immunosorbent assay and immunoblotting. The secretory AChE(s) from S. cervi microfilariae may be utilized for diagnosis of early filarial infections.

Optimisation of immunoaffinity purification of Wuchereria bancrofti specific antibodies from human sera

Immunoaffinity column using Setaria digitata antigens coupled to cyanogen bromide activated Sepharose 4B beads were developed to purify antibodies from sera of filarial patients. Chaotropic (KSCN) ion elution was more efficient for purifying specific antibodies from the column in comparison to ]c elution. Dot blot analysis indicated that purified antibodies showed a high degree of reactivity with cattle filarial antigen and recombinant filarial protein but not with bacterial proteins of E. coli suggesting that the antibodies are specific.

Setaria digitata microfilaraemia in Mastomys coucha: an animal model for chemotherapeutic and immunobiological studies

Intraperitoneal implantation of adult gravid females of the bovine filarial parasite, Setaria digitata in Mastomys coucha was found to induce microfilaraemia lasting for about 125 days. The microfilariae (mf) could be detected as early as 4 days post-implantation (p.i.) and peak levels of about 30 mf in 20 microliters of blood were observed by 21 days. A significant positive correlation was found between mf density and the body weight of recipients pre-implantation. The implanted adult worms were generally viable only for less than 1 week. Implantation resulted in a significant decrease in total leucocytes and erythrocytes, induction of eosinophilia, splenomegaly and anti-erythrocyte autoantibodies. The microfilariae in circulation developed into 3rd-stage infective larvae (L3) when fed onto Aedes aegypti (refm, Liverpool strain). The mf in circulation were found to be eliminated by oral administration of diethylcarbamazine citrate, indicating the usefulness of this model for screening potential anti-microfilarial drugs. During the microfilaraemic phase, priming with tetanus toxoid (TT) resulted in significantly decreased production of anti-toxin levels indicating a state of generalized immunosuppression. Induction of antibodies to various fractionated antigenic components of adult parasites could be demonstrated by enzyme immunoassay (EIA) in M. coucha implanted with live or cold-stunned adult worms. The S. digitata-M. coucha model thus is found amenable to perform chemotherapeutic and immunobiological investigations in experimental filariasis.

Glutathione-binding proteins of Setaria digitata: antibody responses in human infected with Wuchereria bancrofti

Glutathione-s-transferase activity was determined in filarial parasites. The activity was detected in adult stages of cattle parasite Setaria digitata. It was absent in other stages of Setaria and also in infective larval stages of Wuchereria bancrofti and Brugia malayi. The activity was enhanced about twenty five fold following purification of adult setaria extracts on glutathione agarose column. Antibody (IgG and IgM) levels to the affinity purified proteins (SdGBP) were detected predominantly (90%) in Wuchereria bancrofti infected individuals compared with normal residents of endemic regions. IgA and IgE responses could not be detected. Filarial sera in contrast to non-filarial caused reduction in the enzymatic activities of Sd GBP. Microfilaraemic sera after diethylcarbamazine treatment resulted in enhanced reduction of enzymatic activity.

Analysis and potential of excretory-secretory antigens of Setaria cervi for immunodiagnosis of human filariasis

The excretory-secretory (E-LS) products released by the adult Setaria cervi, a bovine filarial parasite, were used to raise polyvalent hyperimmune serum in rabbits. Analysis of E-S products, using anti-E-S serum showed the presence of 10-14 immunogenic proteins, the rabbit anti-E-S serum showed reciprocal antibody titres in the range of 100,000-250,000 by enzyme linked immunosorbent assay. The anti-E-S antibodies could detect circulating antigen in filarial patients sera by Counter immunoelectrophoresis.

Wuchereria bancrofti recombinant antigen-derived poly- and monoclonal antibodies for the detection of circulating antigen(s) in the sera of lymphatic filarial patients

A sandwich antibody ELISA was employed for the detection of circulating filarial antigen in patients with bancroftian filariasis. Wuchereria bancrofti recombinant antigen-derived polyclonal and monoclonal antibodies were successfully used as the revealing antibodies and their efficiency was compared. All the microfilariae (mf) positive (by finger prick and examination of 20 microliters of blood under the microscope) individuals tested showed the presence of circulating antigen(s). Among the antigen positive endemic normals (mf negative by the finger prick method), 43% showed microfilariae by a sensitive parasitological method viz. membrane filtration of the night blood samples. A significant correlation was observed between the parasite antigen levels and the blood microfilaria counts among the mf carriers. This information on the parasite antigen levels could be an ideal monitor to indicate the degree of active infection and in the follow up of chemotherapy.

Allergic reactivity and IgG subclasses to a proteinase fraction of Setaria digitata in filariasis

A low molecular weight fraction (30 KDa) of the cattle filarial parasite Setaria digitata that was earlier demonstrated to have allergenic activity was characterized to be a zinc-dependent cysteine proteinase. Immediate type hypersensitivity (ITH) reaction to the proteinase was evaluated in lymphatic filariasis patients and in endemic controls from Orissa, India. The extent of ITH positivity to the proteinase in infected individuals ranged from 20% in chronic filariasis (CP) patients group to 56% in asymptomatic microfilaraemic carriers (AS). About 62% of endemic normals (EN) were also ITH positive. The serum levels of IgG subclasses were compared in ITH positive and ITH negative filarial patients (AS and CP) as well as in endemic normals (EN) respectively. IgG4 levels were found to be inversely dependent on ITH reaction only in AS groups. Asymptomatic patients (AS) with positive ITH reactivity had lower IgG4 than ITH negative individuals from the same group. The serum levels of other IgG subclasses except IgG2, did not correlate with ITH reactivity. IgG2 levels were higher in ITH negative EN and CP patients but not in the AS group.

Immune response in mice against hatching associated materials from the filarial parasite Setaria digitata (Von Linstow)

The hatching associated materials (excretory-secretory materials (ES)) from filarial parasite S. digitata showed immunosuppression in BALB/C mice on immunization. The material released along with microfilariae (mf) in Tyrode medium showed maximum immunosuppression while that released in presence of sublethal concentration of diethyl carbamazine (DEC, 0.25 mM) showed initial potentiation followed by suppression. While, protein from lysate of embryo zone from which ES materials were released along with the release of mf originate, showed generalized immunopotentiation in BALB/C mice. The latter suggest a change in the nature of materials of embryonic origin before and after the release of mf.

Monoclonal antibodies against antigenic epitopes common between Setaria cervi and Brugia malayi

Several common antigens between the bovine (Setaria cervi) and human (Brugia malayi) filarial parasites have been demonstrated [Immunol Investig, 16 (1987) 139]. Hybridoma cell lines producing monoclonal antibodies against such common antigenic epitopes were obtained by immunizing the BALB/c mice with S. cervi antigen, fusing the spleen cells with Sp2/0 myeloma cells and screening the culture supernatants for antibody against both S. cervi and B. malayi antigens by ELISA. Nine monoclonal antibodies directed against antigenic epitopes common between the bovine and human filarial parasites were identified. Two monoclonal antibodies (I3B4 and I5D6) showed reactivity with the antigen(s) present in filariasis patients serum and thus may have potential for detecting circulating antigen in filaria infected individuals.

Ontogenetic transformation of surface epitope expression, an adaptive immunoevasive strategy of filarial parasites

Filarial nematodes are highly successful in invading, persisting and propagating in human body and eliciting severe ailments. The exact mechanism by which, filarial nematodes evade the host immunity is still ill-defined. The present investigation on the surface antigens of S. digitata revealed the occurrence of shared antigens in the egg, embryo, mf and adult stages. All these stages showed exposed carbohydrate moieties on their surface. In situ localization studies proved that the egg and embryo have exposed surface epitopes whereas the microfilariae and adults did not have any such epitopes. Based on these observations, a model has been proposed on "the surface epitope hiding", as an immunoevasive strategy of the filarial parasite which explains why the naturally shed surface antigens evoke antifilarial immune response in the host even though the system could not recognize the microfilariae or adult parasite due to lack of exposed surface epitopes, permitting the parasite to escape successfully from immune rejection. As treatment with detergents leads to exposure of surface epitopes of parasites, a safe intervention of parasite surface would be an effective strategy for detection and ultimate control of filariasis.

Cloning, over-expression and evaluation of a recombinant fusion protein of Wuchereria bancrofti towards its application as a diagnostic agent for bancroftian filariasis

A low molecular weight (15 kDa) surface antigen of the cattle filarial nematode, Setaria digitata, was earlier shown to be specifically recognized by the antibodies from human bancroftian filarial (Mf positive) patients' sera (Theodore & Kaliraj, 1990). The filarial specific antibodies bound to a 15 kDa peptide in preparative Western blots were eluted and employed in screening of candidate antigens expressed in the genomic library of Wuchereria bancrofti at the IgG4 subclass antibody level. A recombinant clone (lambda WbG7) reacting strongly with filarial sera but poorly with sera from patients infected with non-filarial helminths was selected for further studies. The 2 kb DNA insert of the clone lambda WbG7 was recloned into a pMAL vector and the recombinant clone pGT7 thus obtained was over-expressed and affinity purified. The purified 105 kDa fusion protein of the clone pGT7 was specific and was not recognized by the non-filarial sera at the IgG4 level. All microfilaraemic individuals were positive by IgG4 assay. However, similar attempts to diagnose by filarial-specific IgE assays failed to recognize microfilaraemic individuals. Moreover, by filarial-specific IgG4 assays, the endemic normals were distinctly divided into two groups, showing higher and lower recognition for this antigen indicating current and past/no infection. Among the filarial-IgG4 (assay)-positive 'endemic normals', 14% showed 'microfilariae' during repeated peripheral night blood examination, confirming the validity of the recombinant antigen, pGT7 based assay.

Cellular immune responsiveness in rabbits with Setaria digitata filarial antigen and TDM adjuvant

The purified surface antigens of the bovine filarial parasite Setaria digitata were used as an antigen to immunize rabbits. The aqueous suspensions of trehalose 6-6' dimycolate (TDM) has been successfully used as an effective immunomodulator in experimental studies on filariasis. The effectiveness of such an antigen-TDM combination was demonstrated by enhanced humoral and cellular immunity. Administration of antigen alone shows only humoral immunity. The detectable cellular immune responses further confirm the effect of filarial antigen-TDM combination. The cell-mediated immunity was expressed in vivo by delayed skin reaction and in vitro by leukocyte and macrophage migration inhibition tests.

Antigenic analysis of purified surface antigens of filarial nematode Setaria digitata

The surface antigens of S. digitata were isolated by treatment with Triton X-100. In non SDS-PAGE the surface antigen preparation resolved into more than 6 protein bands. Electroelution of gel slices corresponding to the protein bands with relative mobilities 0.09, 0.32, 0.41, 0.53, 0.61 and 0.76 gave 6 purified surface antigen fractions (SAF). Analysis of SAFs by SDS-PAGE showed that the proteins with molecular weights 17, 29 and 36 KD were the three major polypeptides and different combination of these gave rise to the 6 native surface proteins. The 29 KD protein existed as a monomer and as cross-linked with the 17 and 36 KD proteins. All surface antigen fractions showed antigenicity, where as 29 KD protein remained as a high avidity surface antigen.