Analysis of B. malayi microfilarial antigens by immunoblotting

BALB/C mice were immunized with heavy or low infection of live B. malayi microfilariae or immunised with different fractions of the microfilarial antigens. Antibody levels and antibody dependent macrophage mediated cytotoxicity to B. malayi microfilariae were determined in the immunized sera. Antigens responsible for induction of antibodies were recognised in B. malayi microfilarial extract by immunoblotting. Appearance of cytotoxic antibodies correlates with recognition of certain common antigens in microfilarial extract such as 45, 54, 62, 66 and 76 KDa mol. wt. proteins.

Brugia pahangi: granulomatous lesion development in jirds following single and multiple infections

The development of adult worm burdens and microfilaremias were determined in jirds which received 2, 3, or 4 subcutaneous inoculations of 50 Brugia pahangi infective larvae. Parasite burdens in multiply inoculated jirds were compared to those in four different groups of jirds which received single inoculations of 50 infective larvae. One of each of these singly inoculated groups was infected on the same day that one of the inoculations was given to the multiply infected jirds. Thus, the duration of the infections in the four groups of jirds receiving one inoculation was 54, 118, 189, and 254 days. The development of lymphatic lesions and granulomatous hypersensitivity to B. pahangi antigen was assessed in all jirds at necropsy. The percentage recoveries of adult worms and their locations did not differ in the singly inoculated jirds with infections of different durations. A protective resistance to reinfection, as measured by adult worm recovery in multiply infected jirds, did not occur. The lymphatic lesion scores and numbers of intralymphatic thrombi was greatest in singly inoculated jirds examined 54 days after infection. Pulmonary granuloma areas around adult filarial antigen coated beads embolized in the lungs of jirds 3 days prior to necropsy were also greatest in singly inoculated jirds examined 54 days after infection. Using criteria of lesion scores and lymph thrombi numbers to assess lymphatic lesion severity, a decrease in lesion severity as well as pulmonary granuloma size around antigen coupled beads was seen by 118 days after infection in singly inoculated jirds.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of a monoclonal antibody against infective larvae of Brugia malayi

Monoclonal antibodies were produced following immunization of mice with live infective larvae of Brugia malayi. One of these, 46.08.76, is an antibody that promotes adherence of mouse peritoneal macrophages and human peripheral blood leucocytes to the infective larvae of B. malayi and Wuchereria bancrofti, respectively, and kills them. Fresh normal serum, as a source of complement, augments this effect. The same monoclonal antibody conferred 89% protection to jirds (Meriones unguiculatus) against challenge infection of B. malayi stage-three larvae. This monoclonal antibody recognizes antigens of 80,000, 67,000, 52,000 and 36,000 MW proteins present among the antigens of larvae, as detected by an immunoblotting technique. The antibody also reacts with antigens of infective larvae of Litomosoides carinii, Dipetalonema viteae and B. pahangi, but to a smaller extent.

Enhanced solubilization of immunoreactive proteins from Brugia malayi adult parasites using cetyltrimethylammonium bromide

To determine an optimal method for extracting immunoreactive proteins from filarial parasites, we have subjected Brugia malayi adult worms to a variety of solubilization regimens and compared the results. The parasites were extracted in one of seven detergents (including anionic, cationic, nonionic, and zwitterionic compounds) under varying conditions of pH, detergent concentrations, and incubation time. The individual antigen preparations were then compared both by one-dimensional SDS-PAGE and by immunoblotting analysis using a serum pool from individuals resident in an area endemic for lymphatic filariasis. The cationic detergent cetyltrimethylammonium bromide (CTAB) at 1.0% concentration, pH 7.2, consistently solubilized more proteins immunoreactive with the sera tested. Additionally, CTAB never failed to solubilize immunoreactive proteins solubilized by those other detergents or combinations of detergents studied.

Characterization of stage-specific antigens of infective larvae of the filarial parasite Brugia malayi

Three stages of the filarial parasite Brugia malayi (infective third stage larvae, adult worms, and microfilariae) were analyzed for differences in their protein composition by two-dimensional gel electrophoresis. Comparison of protein profiles of the different stages showed both identical polypeptides (reflecting common proteins) and polypeptides specific for each stage. Three polypeptides present only in infective stage larvae were seen at 72 kDa at an isoelectric point (pI) of 4.98 (p72), 30 kDa at pI 5.5 (p30), and 22 kDa at pI 4.75 (p22). p72 could be labeled chemically with 125I by either chloramine T or IODO-GEN and biosynthetically with [3H]leucine and [35S]methionine during in vitro culture of live larvae; thus, p72 is most likely a surface protein of parasite origin. The antigenic composition of these polypeptides was elucidated by immunoblot analysis. Both p72 and p22 were recognized by hyperimmune rabbit sera to infective larvae; sera from rabbits immunized with adult worms, however, did not recognize any of these Ag. Sera from humans infected with the related Wuchereria bancrofti filaria recognized only p72 and not the other two polypeptides. It therefore appears that p72 is a stage-specific but not genus-specific Ag that is immunogenic in the infected host. p22 also appears to be stage specific and, because it is not recognized by W. bancrofti-infected sera, it may be either a species-specific Ag or a poorly immunogenic molecule of the parasite. With mAb raised to p72, p30, and p22, these proteins were shown to share several antigenic determinants when analyzed by immunoblotting. The shared epitopes were present on numerous molecules with a wide range of apparent m.w. in each of the different parasite stages. Thus, despite the apparent larval stage specificity of these molecules themselves, they must contain certain epitopes shared by molecules from other stages as well. The identification of the p72 polypeptide as a molecule with epitopes exposed on the surface of infective larvae provides a candidate Ag for testing as a protective immunogen.

The effect of sera from cats infected with Brugia pahangi and subsequently treated with levamisole on the infectivity of third-stage larvae of B. pahangi

Cats were treated with levamisole and the infective (L3) stage of Brugia pahangi. Serum from infected cats was subsequently tested for its ability to infect jirds. Jirds autopsied at 33 days postmortem showed significant levels of parasitemia. This is contrary to reports of a previous study wherein serum from humans infected with B. malayi was found to induce cell adherence and death of the L3.

Lymphatic filariasis: detection of circulating and urinary antigen and differences in antibody isotypes complexed with circulating antigen between symptomatic and asymptomatic subjects

A two-site immunoradiometric assay using a monoclonal antibody (MoAb) against Brugia malayi microfilariae allowed the detection of parasite molecules both in the serum and the urine of patients from Sri Lanka infected with Wuchereria bancrofti. Whereas 50% of patients had no antigen in their serum, all of them excreted detectable amounts of antigen in their urine, the levels being higher in symptomatic than in asymptomatic patients. The poor detection in serum appeared to be related to the presence of circulating immune complexes. It was shown that the isotype of the antibodies complexed with the circulating antigen was IgM in the asymptomatic group, while it was mainly IgG in the symptomatic patients (swelling and lymphoedema or elephantiasis). These results suggest the existence of regulatory immune mechanisms affecting the clinical expression of lymphatic filariasis.

Identification of phosphorylcholine epitope-containing antigens in Brugia malayi and relation of serum epitope levels to infection status of jirds with brugian filariasis

The Gib 13 monoclonal antibody was raised against eggs of Onchocerca gibsoni and subsequently found to react with a phosphorylcholine epitope designated as the T15 idiotype. Since an immunoradiometric assay based on the Gib 13 monoclonal antibody holds promise for serodiagnosis of filariasis, the goals of the current study were to evaluate phosphorylcholine epitope production and release by various parasite stages and to assess changes in serum epitope levels during different phases of Brugia malayi infection in jirds. Extracts of B. malayi adult male worms, female worms, and microfilariae contained Gib 13 monoclonal antibody-reactive antigens of Mr 25-30,000, 57-90,000, and approximately equal to 200,000. Adult female worms secreted ten-fold more epitope than microfilariae on a weight basis. Phosphorylcholine-containing antigens were localized in female and male worms, respectively, in egg-bearing regions and the intestines. Assessment of the relationship between serum levels of Gib 13 antibody-binding epitope and parasitologic status of B. malayi-infected jirds showed that the immunoradiometric assay distinguishes patent infected from uninfected control animals, detects a significant rise in epitope level during the prepatent phase of infection, and is unaffected by diethylcarbamazine-induced reduction in the intensity of microfilaremia. There was a direct positive correlation between serum epitope level and female adult worm load. Quantification of serum phosphorylcholine epitope of the T15 idiotype may be useful as an indirect measure of parasite burden in humans with lymphatic filariasis that is independent of microfilaremia.

IgE-dependent killing of Brugia malayi microfilariae by human platelets and its modulation by T cell products

Platelets isolated from patients infected with filariasis were cytotoxic for microfilariae in vitro. Moreover, platelets from normal donors acquired killing properties in the presence of serum from infected individuals. The humoral factor involved in this cytotoxic process was shown to be IgE. This IgE-dependent cytotoxicity of platelets was strongly inhibited by antigen-stimulated T lymphocyte supernatants from filarial patients.

The biochemical and immunochemical characterisation of the 30 kilodalton surface antigen of Brugia pahangi

The major surface antigen (30 kDa) of Brugia pahangi has been characterised by a number of biochemical and immunochemical means. The 30 kDa polypeptide is a glycoprotein which can be extracted from the worm surface by homogenization in the absence of detergents. The 30 kDa polypeptide can be metabolically labelled with [35S]methionine in adult male and female parasites. In addition small amounts of the 35S-labelled 30 kDa antigen can be detected in the medium of worms cultured in vitro. 125I labelling of the excretory-secretory (ES) products of adult male and female parasites followed by immunoprecipitation and peptide mapping has confirmed the relationship between the surface located 30 kDa polypeptide and that released in vitro.

Bancroftian filariasis in Haiti: preliminary characterization of the immunological responsiveness of microfilaremic individuals

Patent infections with the lymphatic filariae, Wuchereria bancrofti and Brugia malayi, are associated with suppressed in vitro cellular responsiveness to filarial antigens. In studies of bancroftian filariasis in Haiti, a significant number of microfilaremic individuals can be characterized as "responders" to filarial antigens. Cells from 37/74 untreated microfilaremic subjects responded to B. pahangi antigen (stimulation ratio greater than 2) as detected by in vitro blastogenesis. A comparison of responders to nonresponders revealed a significant difference in mean B. pahangi reactivity (15,822 vs. 4,538 cpm, P less than 0.001), but no significant differences with respect to age, microfilaremia, PPD or PHA reactivity, or B. pahangi-specific antibody levels. Subtle differences may exist between these groups with respect to recognition of specific antigens on Western blots.

Brugia malayi: recombinant antigens expressed by genomic DNA clones

A Brugia malayi genomic DNA expression library was screened with rabbit antiserum generated against live infective larvae and 33 clones were identified. Five randomly selected clones were characterized in detail by Western blot, DNA and RNA analyses. The fusion proteins produced by each of these recombinant DNA clones are expressed by different genomic sequences. A profile of antigenic cross-reactivities of all 33 recombinant clones was compiled using a battery of antisera, including sera from humans infected with B. malayi. A high percentage of clones were cross-reactive with antisera against the filarial parasites B. pahangi, Dirofilaria immitis, and Onchocerca volvulus. We have made a preliminary identification of three categories of recombinant clones encoding (1) antigens that were cross-reactive with some or all antisera tested, (2) antigens that were specific to the Brugia genus, and (3) antigens that appeared to be specific to B. malayi. These recombinant antigens are candidates for further studies in filarial immunoprophylaxis and diagnosis.

Protective immunity to Brugia malayi larvae in BALB/c mice: potential of this model for the identification of protective antigens

Protective immune responses against the infective larvae of Brugia malayi have been demonstrated in BALB/c mice. Various factors governing resistance to reinfection have been examined to provide baseline data for use of this model in studies of immunoprophylaxis. Parasites that established following a primary infection survived for approximately 10 days, following which numbers declined rapidly to a low level. Resistance was evidenced by a more rapid clearance of secondary infection parasites. The degree of immunity expressed was not related to the route of administration of the initial infection (subcutaneous, intravenous, intramuscular, or intraperitoneal). However, both the level of resistance and the rapidity of its expression were dependent on dose, with as few as 2 larvae stimulating measurable immunity. Sensitization with living male or female adult worms, fourth stage larvae or microfilariae of B. malayi, or infective larvae of B. pahangi conferred substantial resistance to larval challenge. Significant levels of immunity were also induced by dead B. malayi larvae (46%) and their aqueous extracts (76%), but not with the corresponding insoluble fraction. We suggest that this experimental system is ideally suited to aid in the identification of putative protective antigens in brugian filariasis.

IgG antibody subclasses in human filariasis. Differential subclass recognition of parasite antigens correlates with different clinical manifestations of infection

The four subclasses of IgG are distinct in structure, function, and degree of participation in the antibody response to complex antigens. Looking for differential responsiveness of potential pathogenetic significance, we have analyzed both quantitatively and qualitatively the filaria-specific IgG subclass responses of 20 patients with lymphatic filariasis presenting either with chronic lymphatic obstructive pathology and elephantiasis (CP) or with asymptomatic microfilaremia (MF). Subclass-specific monoclonal antibodies were used in an enzyme-linked immunosorbent assay to study IgG filarial antibodies quantitatively and in immunoblot analyses to determine qualitatively the subclass antibody specificities. Quantitatively, the most significant differences among patient groups were in levels of IgG4, which were more than 17 times higher in MF patients (geometric mean, 64.7 micrograms/ml) than in those with CP (mean, 3.7 micrograms/ml). When qualitative analyses were done on the same sera, major differences were noted, particularly in the recognition profiles of the IgG1, IgG3, and IgG4 responses. IgG1 and IgG3 responses to antigens were seen especially to antigens with m.w. greater than 68,000 in all patients with elephantiasis, whereas MF patients showed most of their reactivity to antigens less than 68,000. For IgG4, the MF patients showed prominent recognition of antigens throughout the entire range of m.w., whereas those with CP had very little IgG4 recognition of antigens of any m.w. Interestingly, this relationship was essentially reversed in the IgG3 antibody responses (especially to antigens greater than 68,000) and, to a lesser extent, the IgG1 responses. These findings demonstrate correlations of potential cause/effect significance between IgG4 antibody responsiveness and the immunomodulated asymptomatic MF form of clinical filariasis and between IgG3/IgG1 antibody responsiveness and the clinical presentation of CP.

Complement activation by eggs and microfilariae of filarial parasites

The complement of fresh normal rat serum was activated by filarial eggs and microfilariae (mf). C3 was deposited on the surface of Litomosoides carinii, Brugia pahangi, Brugia malayi and Dipetalonema viteae as seen by immunofluorescence. Intra-uterine and in vitro-derived mf did not bind C3. In contrast, C3 bound to the blood-derived mf of B. pahangi and B. malayi as well as exsheathed mf of L. carinii and B. malayi. Significant consumption of complement was observed with eggs of all filarial species, as well as sheathed mf of B. pahangi, B. malayi and exsheathed mf of L. carinii and B. malayi. These experiments indicated that complement was activated by filarial parasites via the alternative pathway. The bound complement promoted neutrophil-mediated adherence and cytotoxicity.

Characterization of immunosuppressive proteins of Brugia malayi microfilariae

Inhibition of Concanavalin A-induced lymphocyte proliferation was used to monitor the partial purification and characterization of suppressor molecules from microfilariae of Brugia malayi. Suppressor activity was present in high molecular weight fractions of microfilarial extracts (Mr greater than 50 kd on SDS-PAGE) and was protease-sensitive but resisted treatment with sodium periodate, indicating that it is associated with parasite proteins. Suppressor activity was released by microfilariae cultured in vitro and could be detected in peritoneal exudates of intraperitoneally-infected jirds and in lymph and sera from athymic C3H/HeN mice with patent B. malayi infections. These findings indicate that immune unresponsiveness during patent filarial infections may result from the in vivo release by microfilariae of high molecular weight proteins that suppress host immune responses.

Brugia malayi antigens associated with lymphocyte activation in filariasis

Filarial parasites induce immune response in humans which are still poorly characterized. To define the antigens responsible for inducing lymphocyte responses, fast protein liquid chromatography was used to fractionate the antigens of Brugia malayi adult worms which were then tested on lymphocytes from patients with filariasis and normal controls. From an anion exchange column (Mono Q), three peaks of lymphocyte-stimulating activity were eluted which were further fractionated by gel filtration (Superose-12). Peak I induced both a proliferative response as well as the production of filaria-specific antibody in patient lymphocytes. Peak II, capable of inducing only a proliferative response (without antibody production) in patient lymphocytes, was a glycoprotein with phosphocholine as one of the antigenic determinants. Peak III induced proliferative responses in both patient and normal lymphocytes and thus appears to be mitogenic. Two-dimensional gel electrophoresis was then used to identify changes in the major cellular proteins associated with the activation of patient lymphocytes by these partially purified antigens. Stimulation of patient lymphocytes with peak I resulted in increased synthesis of immunoglobulin heavy, light, and J chains. Further, these were the only major secreted proteins found in the culture supernatants. Peak II resulted in quantitative changes in proteins associated with T and not B lymphocyte stimulation. Further analysis of these antigens should help to elucidate the mechanism of host-parasite interaction at both the cellular and molecular levels.

Dynamics of immune responses related to clinical status in Brugia pahangi-infected dogs

Clinical signs of lymph node enlargement, limb edema, lymph duct fibrosis, and microfilaremia were monitored in dogs with chronic Brugia pahangi infections. During the study a single rear limb of each dog was reinfected with multiple low doses of infective larvae. The changing immune responses to parasite antigens prepared from three sources--Brugia pahangi adult worm homogenate extract, adult worm excretory-secretory products, and microfilaria excretory-secretory products--were monitored by Western blot ELISA of antigens fractionated on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and by microtiter plate ELISA. Assays were used to detect antibodies in both the the IgG and IgE classes. A wide range of clinical manifestations was demonstrated in response to reinfection: asymptomatic, amicrofilaremic; asymptomatic, microfilaremic; acute short duration node enlargement and/or limb edema with microfilaremia; and chronic limb edema, amicrofilaremic. On microtiter plate ELISA, the dogs demonstrating the highest anti-adult worm homogenate titers were amicrofilaremic and were asymptomatic or developed chronic limb edema, dogs with high anti-mf ES titers were persistently amicrofilaremic, and the most marked increases against all three antigen sources upon reinfection occurred in low or amicrofilaremic dogs. Quantitative changes in antibody levels against the three crude antigen sources following reinfection were often paralleled by distinct changes in recognition of specific bands of antigens fractionated by SDS-PAGE.

Development of Brugia malayi in Mongolian gerbils previously exposed to Wuchereria bancrofti

Twelve Mongolian gerbils, Meriones unguiculatus, were infected with 100 third-stage larvae of Wuchereria bancrofti. One month later these animals, along with 4 control animals, were given 100 third-stage larvae of Brugia malayi. Eleven of the 12 experimental animals and the 4 controls survived, and 8 of the experimental animals and all of the controls demonstrated microfilaremia after 3 months. The animals were killed at 6-months post-infection and examined for parasites. One W. bancrofti larva was found in one of the experimental animals, and 15% of the B. malayi given were recovered as adults from the testes, viscera, and carcass. Thirty-eight percent of the worms given to the controls were recovered from the testes, viscera, and pelt. The worms from the experimental animals also appeared to be smaller. This study suggests that gerbils are able to develop partial resistance to Brugia malayi following a previous infection with Wuchereria bancrofti.

Circulating parasite antigen(s) in lymphatic filariasis: use of monoclonal antibodies to phosphocholine for immunodiagnosis

Hybridoma cell lines producing monoclonal antibodies (MAb) against a 200 kD antigen found circulating in the sera of microfilaremic patients infected with Wuchereria bancrofti were obtained by immunizing mice with a partially purified antigen preparation. A sensitive MAb (CA101)-based ELISA for measuring circulating parasite antigen was capable of detecting antigen in the sera of 93% of patients with microfilaremia, 46% of those with lymphatic obstruction, and 56% of patients with tropical pulmonary eosinophilia syndrome. Circulating antigen was absent from sera of normal controls, and "false positives" were recorded in only two of 17 patients with nonfilarial helminth infections. By ELISA and immunoblot analysis, it was shown that three of the monoclonals raised to this 200 kD antigen were directed to epitopes of phosphocholine (PC). Two MAb (CA86, CA101) were identified as having the T15 idiotype previously associated with antibodies to the PC of pneumococcal teichoic acid; one was untypeable. All three of these anti-PC MAb reacted with adult, microfilaria, and larval antigen preparations, and by immunoblotting showed multiple banding patterns that indicated the presence of PC determinants on many different antigenic molecules. On the other hand, target antigens of CA101 which were found in the circulation of infected patients were limited to three species with apparent m.w. of 200, 160, and 78 kD. The 200 kD antigen was seen more frequently than the other two antigens. Other T15 anti-PC MAb derived from mice not immunized with filarial antigen showed similar patterns of reactivity with circulating filarial antigen.

Parasite-specific anergy in human filariasis. Insights after analysis of parasite antigen-driven lymphokine production

The antigen-specific immune unresponsiveness seen in bancroftian filariasis was studied by examining lymphokine production in peripheral blood mononuclear cells (PBMC) or PBMC subpopulations from 10 patients with asymptomatic microfilaremia, 13 patients with elephantiasis and 6 normal North Americans. In each group of patients, the kinetics of the lymphokine response and the response to mitogens and nonparasite antigens did not differ significantly. In marked contrast, when antigen-induced lymphokine production was examined, most patients with microfilaremia were unable to produce either interleukin 2 (IL-2) or gamma-interferon (i.e., were nonresponders), and the few who could (hyporesponders, generally with quite low microfilaremia levels) did so at levels significantly less than those of patients with elephantiasis, all of whom showed strong responses to parasite antigen. Removal of neither adherent cells or T8+ cells affected the parasite-specific anergy seen in those with microfilaremia, suggesting a state of T cell tolerance to the parasite in patients with this most common clinical manifestation of bancroftian filariasis.