Parasite antigens in sera and urine of patients with bancroftian and brugian filariasis detected by sandwich ELISA with monoclonal antibodies

We developed a sandwich enzyme-linked immunosorbent assay to detect circulating parasite antigens in human lymphatic filariasis. The assay utilizes a polyclonal rabbit antifilarial antiserum to capture, and a monoclonal antibody to identify, circulating parasite antigen. Using this assay, we found that greater than 95% of sera from microfilaremic donors with bancroftian or brugian filariasis, approximately 60% of sera from microfilaremic patients with hydroceles, chyluria, or elephantiasis, and 15%-20% of sera from asymptomatic residents of filariasis-endemic areas evidently contain filarial antigens. Antigen was also detected in the urine of some microfilaremic patients. Serum levels of antigen detected with one monoclonal antibody, ES34, correlated well with microfilarial density in night blood. In contrast, less than 5% of sera from residents of areas where lymphatic filariasis is not endemic reacted in the assay, even though approximately one-third of the donors whose sera were tested were known to be infected with intestinal nematodes. The assay was designed to be flexible enough to allow the parallel use of multiple monoclonal antibodies with different specificities and simple enough to be applicable in most areas where lymphatic filariasis is endemic.

Induction of lymphatic lesions by Brugia pahangi in jirds with large and small preexisting homologous intraperitoneal infections

The effect of intraperitoneal (i.p.) infections induced by inoculations of 30 or 150 Brugia pahangi third-stage larvae (L3) on the development of infections and lymphatic lesions induced by subsequent homologous subcutaneous (s.c.) inoculations were compared in the present study. Lymphatic lesion severity, as judged by the numbers of lymph thrombi present, and lymphatic lesion scores were significantly reduced in both groups of jirds with existing i.p. infections. The numbers of adult worms that developed, locations of these worms, and the subsequent microfilaremias did not differ significantly between groups. All jirds with i.p. infections developed similar antibody titers to crude somatic adult antigen as measured by ELISA. These levels did not change following s.c. infections. Immediate and delayed footpad swelling responses were also similar in all groups. Results of these experiments support and extend previous studies indicating that i.p. infections of B. pahangi induce a hyporesponsive state in jirds to subsequent s.c. infections without significantly affecting the subsequent parasite burden. This effect appears to be independent of the numbers of L3 inoculated i.p. prior to lymphatic-induced infection. Circulating antibody titers and footpad swelling responses to B. pahangi antigen were not reduced in jirds with the hyporesponsive lymphatic inflammatory response and do not correlate with this condition.

Human in vitro immune reactions to animal filariids

Infective third stage larvae of animal filariids Brugia pahangi and Breinlia booliati incubated in vitro in the presence of normal human peripheral leucocytes and sera from human filariasis subjects resulted in decrease in motility, cell adherence, and formation of precipitates around the larvae. Strongest immune reactions were seen with sera from amicrofilaraemic symptomatic subjects, normal exposed individuals, and patients with tropical pulmonary eosinophilia syndrome (TPE). Weaker reactions were observed with sera from patients with elephantiasis. In all cases, reactivity to B. pahangi larvae was considerably higher than against B. booliati. Sera from microfilaraemic patients and unexposed control subjects were nonreactive. The implication of these human in vitro immune reactions against filarial parasites of animal origin is discussed in the context of the hypothesis of "zooprophylaxis" previously suggested by other workers.

Brugia pahangi in nude mice: protective immunity to infective larvae is Thy 1.2+ cell dependent and cyclosporin A resistant

Mechanisms of protective immunity to larvae of Brugia pahangi were studied in congenitally athymic nude C3H/HeN mice and their syngeneic heterozygous littermates. An average 11% of subcutaneous larval inocula was recovered from control nudes 28 days after inoculation. No worms were recovered from nude recipients of viable splenic Thy 1.2+ T lymphocytes from heterozygotes which had killed a priming dose of B. pahangi larvae. Primed T lymphocytes, depleted of either Lyt 1.1+ or Lyt 2.1+ cells or incubated with anti-Thy 1.2 monoclonal antibody and complement, failed to protect nude mice against a larval challenge. Nor were primed B lymphocytes depleted by Thy 1.2+ T cell contaminants protective. Treatment with cyclosporin A (CsA) did not increase the numbers of worms recovered from heterozygotes nor did CsA treatment of heterozygous cell donors abolish the ability of primed Thy 1.2+ T lymphocytes to transfer protection to nude mice. IgG but not IgM antibody titres to B. pahangi antigens were depressed in all CsA-treated mice. CsA treatment of nude mice had no direct effect upon development of B. pahangi larvae. These results show that protective immunity to larvae of B. pahangi in mice depends upon small numbers of Thy 1.2+ T cells which are CsA-resistant.

Platelets mediate the action of diethylcarbamazine on microfilariae

More than 400 million people in the world are infected by filarial parasites leading to a wide range of pathologies. Although introduced in 1947, the mainstay of the therapy and control of the filariases is diethylcarbamazine (N,N-diethyl-4-methyl-1-piperazine carboxamide; DEC), the mode of action of which still remains unknown despite widespread use and intensive laboratory investigations. The marked contrast between an extremely rapid action in vivo and the absence of any significant activity on microfilariae in vitro is unique among chemotherapeutic agents. DEC has been thought to modify the surface layer of the microfilariae and expose them to immunological cell-mediated lysis. This report provides the first evidence that the effect of DEC is mediated by blood platelets with the additional triggering of a filarial excretory antigen (FEA). The killing mechanism is antibody-independent and involves the participation of free radicals.

Immunochemical characterization and biosynthesis of major antigens of iodo-bead surface-labeled Brugia malayi microfilariae

The objectives of the present study were to identify and characterize biochemically the major antigens of Brugia malayi microfilariae, a filarial parasite that infects humans. IgG antibodies in sera of mice which had cleared parasites from the bloodstream reacted with 30, 55, 94 and 150 kDa molecules of living microfilariae radioiodinated by the Iodo-bead method. Sera of humans infected with the related filariae Wuchereria bancrofti, Loa loa or Onchocerca volvulus immunoprecipitated molecules of similar size as well as two additional proteins of 22 and 43 kDa. Sera of uninfected North Americans or mice infected with Trichinella spiralis or Schistosoma mansoni did not recognize these radioiodinated antigens. Experiments to examine the possible surface localization and metabolism of these antigens showed that they were removed from intact parasites exposed to chymotrypsin or trypsin and that immunogenic molecules of 30, 55, and 150 kDa were released into excretory-secretory products by viable microfilariae. [35S]Methionine biosynthetically labeled polypeptide antigens of 22, 30, 35 and 150 kDa were detected by antibody reacted with intact microfilariae and/or their excretion products. Antigens of 30, 55, and 150 kDa appear to be glycoproteins as they bound wheat germ agglutinin and were biosynthetically labeled with [14C]N-acetyl-D-glucosamine. These data suggest that the surface of B. malayi microfilariae is a dynamic structure which synthesizes and sheds antigens.

Reaginic and homocytotropic IgG antibody response of Mastomys natalensis in experimental infections of filarial parasites (Litomosoides carinii, Dipetalonema viteae, Brugia malayi, B. pahangi)

Reaginic and homocytotropic IgG antibodies in sera using passive cutaneous anaphylaxis (PCA) test and antigen from Litomosoides carinii were followed in Mastomys natalensis, infected with L. carinii, Dipetalonema viteae, Brugia malayi or B. pahangi. Groups of animals with infections of various ages so as to cover a total infection period of up to 300 to 420 days post-infection (p.i.), depending on the species of parasites, were bled at 1- to 3-week intervals over periods of 50-112 days. In addition, intradermal tests were performed on animals infected with L. carinii to detect immediate type hypersensitivity. Reaginic antibodies were usually first detected in the 3rd week after infection. Thereafter, a marked increase of PCA titres was observed in the 4th week p.i. leading to maximum titres 4 weeks after infection with D. viteae and B. pahangi and 6 weeks after B. malayi infection. Mean maximum titres were between 1:40 and 1:160. Following the peak response, titres decreased markedly until the beginning of patency in infections with D. viteae, B. malayi and B. pahangi whereas a constant course was observed at this time in animals infected with L. carinii. A further rise in PCA titres occurred in all infections around the beginning of patency, resulting in maximum reagin levels in L. carinii infections (mean titre 1:80) and moderate titres in the other infections. During early patency there was an inverse relationship between microfilaraemia density and levels of reaginic antibodies. However, in the phase of decreasing parasitaemia in L. carinii infected animals, microfilariae counts and PCA titres were directly correlated. Homocytotropic IgG antibodies showed relatively constant PCA titres of about 1:20 in L. carinii infected Mastomys throughout the observation period. In D. viteae infections they were demonstrated at 30 days p.i., reaching titres of about 1:40. B. malayi infected animals showed a maximum titre of 1:40 40 days p.i.. Thereafter, titres decreased continuously and homocytotropic IgG antibodies were absent at 110 days p.i.. High titres were observed at day 150 but thereafter sera were negative. B. pahangi infected animals showed moderate titres (1:5) 35 days p.i.. Thereafter, antibodies were found at low titres until 115 days p.i.. Intradermal reactions in L. carinii infected animals generally increased in size from 30-60 but decreased when microfilariae appeared in the blood.(ABSTRACT TRUNCATED AT 400 WORDS)

Functional and antigenic maturation of Brugia malayi microfilariae

Brugia malayi microfilariae of specified ages were obtained from gerbils implanted with fertile adult worms. Such microfilariae were tested for their capacity to infect mosquitoes. A strong age dependence was found for the microfilariae's capacity to: penetrate the mosquito midgut, exsheath in response to 20 mM calcium, and develop to third stage larvae in the mosquito. In addition, differences were found between 2-day-old microfilariae and controls (from larva-infected gerbils) in their reactivities with a series of monoclonal antibodies. Thus, defined immunochemical changes occur in microfilariae as they assume functional maturity.

Detection of circulating and urinary antigens in Mastomys natalensis experimentally infected with Brugia malayi, Brugia pahangi, or Litomosoides carinii

The time-course of the detection of circulating and urinary filarial antigens was followed with a 2S-IRMA assay, using a mouse monoclonal antibody raised against Brugia malayi larvae, in Mastomys natalensis experimentally infected with Brugia malayi, Brugia pahangi, or Litomosoides carinii. In the prepatent phase of the infections, filarial antigen was detected 4-7 weeks before microfilariae appeared in the peripheral blood. Moreover, the sensitivity of the test was greater with urine than with serum. During the patent phase of infection, the level of circulating antigens detected varied considerably. However, there was a positive correlation (P less than 0.05) between antigenemia and microfilaremia. In L. carinii infection, filarial antigen could be easily detected in spite of the disappearance of microfilariae in peripheral blood, 49 weeks post infection. If these results are extrapolated to man, the 2S-IRMA should be useful for epidemiological surveys in endemic areas where transmission has been eliminated.

Phosphorylcholine-bearing antigens in filarial nematode parasites: analysis of somatic extracts, in-vitro secretions and infection sera from Brugia malayi and B. pahangi

A set of cross-reactive antigens is described which are present in somatic extracts and in-vitro secretions of the filarial nematodes Brugia pahangi and B. malayi. A monoclonal antibody reactive with a repeating epitope on these molecules readily detects circulating antigen in the serum of animals infected with lymphatic filariae, using either an immunoradiometric assay or enzyme-linked immunosorbent assay (ELISA). This epitope has the immunological reactivity and chemical characteristics of the phosphorylcholine (PC) hapten. The anti-PC monoclonal has been used to define the antigens bearing this epitope, and in chromatographic studies on material from extracts of Brugia adult worms, a heterogeneous profile of PC-positive molecules are found. In sera from Brugia-infected jirds, an antigen with a native molecular weight of approximately 500,000 is observed, which displays limited sensitivity to protease degradation. However, denatured samples on Western blots show a major parasite circulating antigen of Mr 90,000. The detection of this antigen in the presence of excess host antibody is also demonstrated, taking advantage of the stability of the target epitope to a range of treatments designed to dissociate and eliminate immune complexes.

The Wellcome Trust lecture. Inflammatory responses to filarial connective tissue parasites

The inflammatory responses to lymphatic filariae and to Onchocerca volvulus are reviewed with particular attention to evolutionary biology; inflammatory host spectrum; non-specific components; immunoregulation; immune evasion versus immunomodulation; chronic tissue damage and scarring and disease models. Basic principles of pathogenesis are emphasized, comparisons drawn with schistosome infection, and critical items of missing information are highlighted.

Antigenic characterization of adult Wuchereria bancrofti filarial nematodes

Adult Wuchereria bancrofti were recovered from infected Presbytis cristatus monkeys and radio-isotope labelled extrinsically with 125I and in vitro with [35S]methionine. 125I labelling of the surface of adult W. bancrofti permitted a comparison between the major surface antigens of this species and those from the related lymphatic filariae, Brugia malayi and B. pahangi. All species bear a prominent Mr 29,000 surface antigen but among the differences observed were the strongly labelled molecules with Mr 58,000 and 67,000 in W. bancrofti which are extremely faint in the Brugia species. The [35S]methionine label was effectively incorporated into somatic parasite proteins in vitro although it was not possible to identify any secreted proteins in this way. The antigenicity of these products was investigated using a variety of sera from homologous and heterologous infections and the immunoprecipitation patterns highlighted particular differences between somatic proteins of male and female worms. One secreted antigen was detected, however, by virtue of its phosphorylcholine epitopes, in the culture medium of mixed adult worms; medium from male W. bancrofti adults was negative although homogenates of either sex of adult W. bancrofti were strongly positive in the same system.

Brugia malayi: rat cell interactions with infective larvae mediated by complement

Albino rat macrophages and neutrophils, in the presence of fresh normal rat serum as a source of complement, adhered to and promoted killing of Brugia malayi infective larvae in vitro. Eosinophils, by themselves, were marginally cytotoxic at a high cell-target ratio but promoted cytotoxicity when mixed with macrophages. Eosinophil culture supernatants enhanced the macrophage mediated killing of infective larvae. The complement of fresh normal rat serum was found to act by the alternate pathway. Fresh normal rat serum depleted of alternate pathway complement activity by treatment with zymosan A, or of Factor B by heating at 50 C for 20 min, or of Factor D by passing through Sephadex G75 column, failed to promote cell adherence to the parasite. C3 molecules were detected on the surface of infective larvae by immunofluorescence. There was a significant consumption of complement when Brugia malayi infective larvae were incubated in fresh normal rat serum. Albino rat cells were more potent in inducing cytotoxicity to infective larvae in vitro than those from jird or Mastomys natalensis, which may reflect the greater resistance offered by the rat to B. malayi infection. There was much less cellular infiltration on introduction of Brugia malayi infective larvae into the peritoneal cavity of jirds compared to rats and Mastomys natalensis indicating the greater susceptibility of jirds to intraperitoneally induced infections.

Ultrastructural observations on the fate of Brugia malayi in jirds previously vaccinated with irradiated infective stage larvae

Vaccination of inbred jirds (Meriones unguiculatus) with 60cobalt radiation-attenuated Brugia malayi infective stage larvae (L3) protected against homologous challenge given either subcutaneously (sc) or by the intraperitoneal route (ip). At necropsy numerous nodules were recovered from the peritoneal cavities of jirds which had been vaccinated sc and challenged ip. Histopathologic analysis showed these to be granulomas containing dead and dying larvae and transmission electron microscopy showed that eosinophils were present in high numbers around and within the larvae. Structural damage to the L3 cuticle was apparent in discrete areas and eosinophils actively entering the breached cuticle at the time of fixation were observed. Coalescence of eosinophil secretion granules and the formation of degranulation vacuoles were seen in eosinophils throughout the granulomas. Degranulation resulted in the deposition of electron-dense material on the surface of the larval cuticle. The jird vaccine model for B. malayi thus appears to be a potentially useful tool for investigation of immune mechanisms in filariasis.

Clearance of inoculated microfilariae of Brugia malayi by monoclonal antibodies in BALB/c mice

A stable and long-lasting microfilaremia was developed by intravenous injection with 2 X 10(5) microfilariae (mf) of Brugia malayi into BALB/c mice. Mf density in mice was maintained at least at 30 to 40 mf/20 microliter blood for 4 weeks, then gradually decreased as the same as in the jird. However, mf inoculated were cleared from the blood within 3 weeks in the mice which was immunized with repeated intravenous injections with live mf. The effect of mf clearance was passively transferred into the mice with inoculated microfilaremia by intravenous injection of 0.2 ml serum from the immunized mice. For the analysis of the role of anti-mf antibodies, monoclonal antibodies (MABs) against mf of B. malayi were produced. An IgG1 MAB gave a significant mf reduction in mice and it promoted in vitro adherence of normal mouse spleen cells to mf.

Brugia pahangi infections in cats: antibody responses which correlate with the change from the microfilaraemic to the amicrofilaraemic state

The humoral responses of eight cats infected with Brugia pahangi to somatic antigens from all life-cycle stages were examined quantitatively by ELISA and qualitatively by immunoblotting for almost a year post infection. Six cats spontaneously became amicrofilaraemic: their production of IgG antibodies against somatic antigens of microfilariae, adults, and infective larvae was not statistically higher than that of the two cats which remained microfilaraemic. However, immunoblotting revealed that those cats which spontaneously became amicrofilaraemic selectively recognized certain microfilarial, adult and infective larval somatic antigens prior to disappearance of microfilariae from the peripheral circulation. The data suggest that selective recognition of antigens by some cats is responsible for the production of antibodies which may then promote microfilarial death.

Attempted vaccination of jirds (Meriones unguiculatus) against Brugia pahangi with radiation attenuated infective larvae

Jirds were vaccinated by three to five subcutaneous (SC) injections of infective larvae of Brugia pahangi which had been irradiated at 25, 45 or 90 krads from a 60Co source. They were challenged either SC or intraperitoneally. Vaccination with four doses of 50 larvae irradiated with 25 krads produced 49.3% resistance to IP challenge worms and 39.8% against SC challenge worms. Five doses of larvae irradiated with 45 krads produced 62% resistance to SC challenge. Three doses of larvae irradiated with 90 krads produced 74.9% resistance to SC challenge and five doses produced 76.2% resistance. The reasons why irradiated larvae produce resistance whereas normal larvae do not are discussed.

Differential recognition of a protective filarial antigen by antibodies from humans with bancroftian filariasis

The objectives of this study were to identify filarial antigens which induce enhanced clearance of circulating microfilariae and to establish if human antibody reactivity with these molecules correlates with the apparent parasite burdens of residents of an endemic area of Bancroftian filariasis. Mice immunized with an extract of Brugia malayi microfilariae develop IgG antibodies to four major filarial antigens with an apparent molecular weight (Mr) of approximately 112,000, 60,000, 45,000, and 25,000. Animals immunized with gel slices containing the approximately 25,000-Mr antigen are resistant to intravenous challenge with live microfilariae (78-98% reduction in parasitemia vs. controls, P less than 0.01). A group of 22 amicrofilaremic humans had a significantly higher (P less than 0.025) mean antibody titer to the Mr 25,000-Mr antigen (1: 424) than 16 microfilaremic individuals (1:95). There were no significant differences between the two groups in antibody titers to filarial antigens of Mr approximately 112,000, 60,000, and 45,000 Mr. These data suggest that a high degree of reactivity to the 25,000-Mr antigen in humans with lymphatic filariasis correlates with a parasitologic status that is least conducive to transmission of infection.

Lack of biological significance of in vitro Brugia malayi microfilarial cytotoxicity mediated by Propionibacterium acnes ("Corynebacterium parvum")-and Mycobacterium bovis BCG-activated macrophages

The effect of nonspecific activation of host macrophages by Propionibacterium acnes ("Corynebacterium parvum") or Mycobacterium bovis BCG on Brugia malayi microfilariae was determined by in vitro and in vivo studies. Intraperitoneal injection of C. parvum or BCG stimulated peritoneal exudate cells, which were toxic to microfilariae. Microfilariae were equally susceptible to damage by C57BL/6J or BALB/cJ peritoneal exudate cells. Furthermore, inhibitors of oxidative metabolism and arginine supplementation did not prevent this toxicity, suggesting that the mechanism of microfilarial damage differs from that seen with another multicellular helminth, Schistosoma mansoni. In vivo studies with both BCG and C parvum, however, did not confirm the importance of nonspecific immunity in resistance to B. malayi microfilaremia. Despite the lack of biologic relevance of this phenomenon, in vitro studies may yield important knowledge about the mechanisms of microfilarial damage.

Detection of circulating parasite antigen in bancroftian filariasis by counterimmunoelectrophoresis

We used counterimmunoelectrophoresis (CIEP) with rabbit antibodies to Dirofilaria immitis and Brugia malayi to detect soluble filarial antigen in sera collected in a Wuchereria bancrofti-endemic area in South India. Filarial antigen was detected in 38 of 38 sera from microfilaremic patients, 3 of 48 sera from amicrofilaremic patients with lymphatic pathology, and 3 of 5 sera from former microfilaria carriers with negative blood examinations 6 months or more after diethylcarbamazine therapy. One of 32 endemic control sera, 0 of 35 nonendemic sera, and 0 of 20 B. malayi sera were positive. Antigenemia was equally detectable in sera collected at night or during the day (when microfilariae are absent from the blood). Parasite antigen was also detected in the urine of patients with positive serum tests. Antibodies to circulating filarial antigen (also detected by CIEP) were absent in all but 2 antigen-positive sera but present in 22 of 45 antigen-negative sera from clinical filariasis patients and in 9 of 31 antigen-negative sera from endemic controls. Parasite antigen detection by CIEP appears to be a sensitive, specific, and practical diagnostic test for active W. bancrofti infection.

Secreted and surface antigens from larval stages of Wuchereria bancrofti, the major human lymphatic filarial parasite

Antigenic proteins of microfilariae and infective larvae of Wuchereria bancrofti have been identified by intrinsic and extrinsic radiolabelling, and specific immunoprecipitation with sera from filarial patients. From 125I surface-labelling experiments, the most prominent antigen on both stages is of relative molecular mass (Mr) 17 000, while a molecule of similar size is both synthesized and released in vitro following labelling with [35S]methionine. A second similarity between the two stages is the production and secretion of a Mr 21 000 component, which is, however, not detected on the worm surfaces. A series of additional proteins from larval W. bancrofti are described from each parasite compartment (secreted, surface and somatic) and the antigenicity and specificity of these components explored with serum from patients with filariasis due to W. bancrofti or Brugia species, and with onchocerciasis. Among additional molecules released in vitro we have found a Mr 51 000 antigen from both stages, and also several proteins which are not recognised by antibody from human filarial patients.