Detection of filaria-specific IgG4antibodies and filarial DNA, for the screening of blood spots forBrugia timori

The establishment of simple, sensitive and specific tools for the diagnosis of brugian lymphatic filariasis is a prerequisite for a successful intervention to control the disease. In the simple and rapid Brugia Rapid (BR) test, an immunochromatographic dipstick is used to detect IgG(4) antibodies that are reactive with a recombinant Brugia malayi antigen. When sera from 109 individuals with Brugia microfilaraemias (12 with B. malayi and 97 with B. timori) were investigated using the BR test, all were found positive. In contrast, all of the 150 sera from individuals with Onchocerca volvulus or Mansonella infections investigated were found negative in BR tests. Some unwelcome cross-reactions were observed, however, with sera from individuals infected with Wuchereria bancrofti (three of 12 test-positive) and Dirofilaria (one of nine test-positive). In an attempt to facilitate sample collection and detect any cross-reactions, the BR dipstick was used to screen blood spots, that had been allowed to dry on filter paper, for B. timori microfilariae, before the dipstick-positive samples were tested with a PCR-based assay. Of the 66 individuals so tested, 37 (56%) were found positive by the BR test used on dry blood spots and eight (22%) by the filtration of fresh blood samples. Only nine of the 37 dipstick-positive samples were found PCR-positive. The combined use of BR tests and PCR-based assays, for testing blood spots in areas where brugian filariasis is endemic, appears to be a promising method not only for post-treatment monitoring but also for the certification activities planned within the framework of the Global Programme to Eliminate Lymphatic Filariasis.

Duration of detection of anti-BmR1 IgG4 antibodies after mass-drug administration (MDA) in Sarawak, Malaysia

The detection rates of brugian filariasis in three regions of Sarawak namely Central, North and South after three courses of mass drug administration (MDA) from year 2004 to 2006 was investigated. A recombinant BmR1 antigen-based IgG4 detection test, named Brugia Rapid and night blood smear for microfilaria (mf) detection were used. All three regions recorded a sharp fall in mf positive rates after a year post-MDA. Meanwhile Brugia Rapid positive rates declined more gradually to 3.8% and 5.6% of the pre-MDA levels in the Central and North regions, respectively. This study showed that in filariasis endemic areas in Sarawak, anti-filarial IgG4 antibodies to BmR1, as detected by the Brugia Rapid test, were positive for one to two years after mf disappearance.

Antibody responses to human lymphatic filarial parasites

The lymphatic filarial parasites, Brugia and Wuchereria, continue to present an immunological puzzle, particularly with respect to the development of natural resistance or damaging disease. We have approached this question by examining humoral responses to a few defined antigens of selected interest from these parasites, using sera from each category in the spectrum of filarial disease. Many antigens, such as the major adult surface protein of Mr 29,000 (29K), appear to be recognized at all stages of infection, but two components show interesting patterns of differential recognition. A triplet of proteins of Mr 65-75K associated with the microfilarial surface is preferentially bound by serum from patent microfilaraemic infections, whereas an unrelated 75K protein has been found to react only with antibody from amicrofilaraemic individuals. In general, however, the data obtained so far emphasize the importance of undertaking an antigenic analysis at the level of single epitopes. Such studies are now under way using recombinant proteins expressed in bacterial hosts.

The cat infected with Brugia pahangi as a model of human filariasis

The responses of cats to Brugia pahangi, which parasitizes them in nature, mimic those of humans to Brugia malayi and Wuchereria bancrofti in many important respects. It is likely that many of the features of the relationship between host and parasite that can be studied in cats infected with B. pahangi also apply to humans, but for a variety of practical reasons cannot be demonstrated in humans. Both immunologically and parasitologically there is a profound difference between B. pahangi-infected cats that have microfilariae in their blood and those that either do not become microfilaraemic or clear their blood of microfilariae and become post-microfilaraemic. Microfilaraemic cats are susceptible to reinfection and fail to recognize the surface of the sheath of microfilariae. They also do not produce antibodies against several components recognized by post-microfilaraemic cats. Cats that have destroyed their microfilariae also destroy their adult worms and are very resistant to challenge with infective larvae. Apart from the unique ability to recognize the sheath of microfilariae in fluorescent antibody tests, sera from these cats react with microfilarial antigens at 61-81 kDa, antigens of infective larvae at 22 and 18.5 kDa and adult antigens at 34, 18, 16, 13 and 11.5 kDa. None of these antigens are recognized by microfilaraemic cats.

Regulation of immune responses in lymphatic filariasis

The nature and intensity of immune reactions to filarial antigens appear to be controlled by two broad mechanisms: immunoregulation and immune tolerance. Parasite molecules of high molecular weight activate suppressor T lymphocytes; suppressive parasite products are present in sera from microfilaraemic patients. Prenatal or perinatal exposure to soluble parasite antigens may influence a person's future ability to react to filarial antigens.

Use of Brugia Rapid dipstick and ICT test to map distribution of lymphatic filariasis in the Democratic Republic of Timor-Leste

The newly-introduced Brugia Rapid dipstick for filarial antibodies and ICT filarial antigen card test were used to confirm historical data on the distribution of lymphatic filariasis in the Republic of Timor-Leste. Twelve out of thirteen districts were confirmed as being endemic. Brugian filariasis predominates, with an average prevalence of 11.6%. The average prevalence of Bancroftian filariasis was 1.1%. The study demonstrated that the Brugia Rapid test can provide useful information about the distribution of Brugian filariasis in circumstances where it is difficult or impossible to obtain night blood samples for microfilariae.

Detection of IgG antibodies of Brugian filariasis with crude male and female antigens of Dirofilaria immitis

Crude antigens from male and female Dirofilaria immitis were used to detect antibody to Brugian filariasis in humans by indirect ELISA. Both antigens were tested with 42 cases of Brugian filariasis, 131 cases of 20 heterologous infections and 35 healthy controls. The results--using male and female antigens--showed sensitivity of 88.1% and 88.1%, and specificities of 64.1% and 51.8%, respectively. Cross-reaction from other helminthic infections using crude male antigen gave false-positives with 48 sera from 13 heterologous diseases at the threshold value of 0.180, while the female antigen gave 63 sera from 15 diseases, at 0.309. Serum antibodies from patients with other helminthic infections--gnathostomiasis, strongyloidiasis, hookworm infections, trichinellosis, capillariasis, angiostrongyliasis, ascariasis, trichuriasis, toxocariasis, neurocysticercosis, cystic echinococcosis, taeniasis and opisthorchiasis--resulted in false-positives with both male and female antigens. One each of sparganosis and paragonimiasis heterotremus sera cross-reacted with only crude female antigen and their OD values were close to the threshold value. Although crude male antigen showed better specificity than crude female antigen, both female and male worms are sources of antigens needed for further purification. This study provides baseline data for further serodiagnosis of Brugian filariasis using dirofilaria antigen.

Lymphatic filariasis and Brugia timori: prospects for elimination

Brugia timori is a pathogenic filarial nematode of humans, replacing the closely related species Brugia malayi on some islands in eastern Indonesia. Recent studies on Alor island show that, locally, B. timori is still of great public health importance, causing mainly acute filarial fever and chronic lymphedema. PCR-based assays to detect parasite DNA, in addition to assays for detecting specific antibodies that have been originally developed for B. malayi, can be used efficiently as diagnostic tools for B. timori. In the framework of the Global Program to Eliminate Lymphatic Filariasis, a single annual dose of diethylcarbamazine, in combination with albendazole, was found to reduce the prevalence and density of microfilaraemia persistently. Therefore, elimination of B. timori appears to be achievable.

Detection of filaria-specific IgG4 antibodies using Brugia Rapid test in individuals from an area highly endemic for Brugia timori

The filarial parasite Brugia timori is of great public health importance in some islands of Eastern Indonesia. To establish a simple serological test for the identification and post-treatment monitoring of areas endemic for B. timori, a rapid immunochromatographic dipstick test (Brugia Rapid, BR) was evaluated on microfilaraemic and amicrofilaraemic individuals. This test is based on the detection of anti-filarial IgG4 antibodies that react with a recombinant Brugia malayi antigen (BmR1). In our study area on Alor island the prevalence of microfilaraemia was 26%. With the BR test, 100% of 196 sera from microfilaraemic persons and 76% of 563 sera from amicrofilaraemic persons, either symptomatic or asymptomatic, reacted positive. All 50 control sera from areas non-endemic for lymphatic filariasis gave negative BR test results. This study showed that the BR test can be also used to detect antibodies against B. timori. Due to the high prevalence of IgG4 antibodies as detected by the BR test (81%), no significant correlation with the prevalence of microfilaraemia could be detected within the endemic village. The BR test also shows great promise to be employed as a monitoring tool for B. timori in the framework of the Global Program to Eliminate Lymphatic Filariasis (GPELF).

The role of endosymbiotic Wolbachia bacteria in filarial disease

In this review, we describe the pathogenic role of Wolbachia endosymbiotic bacteria in filarial diseases, focusing on the host innate immune responses to filarial and Wolbachia products. A description of the host pathogen recognition and early inflammatory responses including TLR4-mediated signalling, chemokine and cytokine responses and inflammatory cell recruitment is provided from human studies and from animal models of filarial disease. Finally, the impact of the discovery and characterization of Wolbachia on filarial research and treatment programmes is discussed.

Immunity to filarial nematodes

Mosquito-borne filarial nematodes cause the severe, debilitating disease of human lymphatic filariasis. In areas endemic for this disease, differential responses range from putative immunity through asymptomatic microfilaraemic infection to chronic pathology. Current research in mouse models of infection is elucidating the immunological mechanisms that can lead to immunity against this disease. In this review, the importance of different immunological pathways are discussed in relation to their role in human disease and in terms of their ability to kill separate developmental stages of the filarial parasite.

The third-stage larva (L3) of Brugia: its role in immune modulation and protective immunity

In this review, we focus on the role of the L3 (third-stage larva) of lymphatic filarial nematodes in immunomodulation and in the development of protective immunity. Studies in the mouse models of Brugia have been fundamental to our understanding of the mechanisms by which infection with L3 results in Th2 responses and the active suppression of Th1 responses. The relevance of these phenomena to the human infection is discussed.

Adverse reactions following diethylcarbamazine (DEC) intake in 'endemic normals', microfilaraemics and elephantiasis patients

This paper reports on adverse reactions following a 12-day course of 6 mg/kg diethylcarbamazine (DEC) therapy in brugian filariasis patients in Indonesia. Microfilaria-positive individuals (n = 26), 'endemic normals' (n = 12) and elephantiasis patients (n = 17) were included in the study. Fever, headache and body aches started between 2 and 24 h after DEC intake. Adverse reactions were categorized into 'no or mild', 'moderate' or 'severe' depending on the total reaction score. Four microfilaraemic individuals (15.4%) suffered from severe adverse reactions and their pre-treatment microfilarial levels (geometric mean, GM = 3060 mf/10 mL) were significantly higher than in the 5 microfilaraemic individuals (19.2%) suffering from moderate reactions (GM = 1268 mf/10 mL) and in the 17 microfilaraemic patients (65.4%) who experienced no or mild reactions (GM = 6 mf/10 mL)(P < 0.001 and P < 0.001, respectively). Endemic normals showed no or mild adverse reactions. No or mild adverse reactions were also recorded in all but 2 elephantiasis patients after DEC intake. Two elephantiasis patients with moderate reactions had high levels of circulating microfilariae at pre-treatment (2097 and 7375 mf/10 mL). Concentrations of DEC were measured in plasma, but could not explain the differences in the severity of adverse reactions.

The L3 of Brugia induces a Th2-polarized response following activation of an IL-4-producing CD4-CD8- alphabeta T cell population

Lymphatic filariasis in man is characterized by a profound bias in the immune response. Parasite-specific Th1 responses are dramatically down-regulated while Th2 responses dominate. We have used the infective larval stage of the nematode parasite Brugia pahangi, a potent Th2 inducer in naive mice, to examine cytokine production during the initiation phase of the response. For comparative purposes, the early cytokine transcription pattern elicited by microfilariae (mf), another life cycle stage of the parasite known to induce a primary Th1 response, was analysed in parallel. At 24 h post-infection (p.i.) a burst of IL-4 transcription was detected in the draining popliteal lymph node of L3-infected animals. IL-4 was the only cytokine transcript detectable at this early time point and was not present in mf-infected mice. From day 4 p.i. onwards, the L3 elicited a Th2 response as defined at the level of cytokine mRNA and protein production by CD4+ cells. In contrast, mf stimulate high levels of IFN-gamma mRNA at day 4 p.i. in the absence of IL-4 or IL-10 induction. Cell selection analysis indicated that IL-4 produced at 24 h derived from a population of CD4-CD8- alphabeta T cells. These results suggest that triggering of an unusual double-negative T cell population to secrete IL-4 at the very outset of infection with the L3 of B. pahangi may be the critical factor favouring the development of antigen-specific Th2 cells in response to this stage of the parasite.

Zoonotic Brugian lymphadenitis. An unusual case with florid monocytoid B-cell proliferation

Human infection with a zoonotic Brugia species in the United States is uncommon. Positive identification of the filarial nematode is required for histopathologic diagnosis. Many cases may go unrecognized because of the nonspecific clinical manifestations and the nondiagnostic histologic changes occurring in involved lymph nodes. A case of zoonotic Brugia lymphadenitis is described in a patient from Rhode Island, in which a small nongravid female worm was identified in a lymph node biopsy specimen. The lymph node also showed a spectrum of reaction changes including the presence of florid monocytoid B-cell proliferation, which has not been described in association with zoonotic Brugian filariasis.

Differential antibody isotype reactivity to specific antigens in human lymphatic filariasis: gp15/400 preferentially induces immunoglobulin E (IgE), IgG4, and IgG2

Lymphatic filarial infection in humans is associated with a strong skewing of the immune response towards the TH2 arm, with prominent interleukin 4-producing cells and elevated levels of immunoglobulin G4 (IgG4) and IgE antibodies in peripheral blood. To determine how such a generalized TH2 imbalance governs responses to individual parasite antigens, the profiles of isotypes of antibodies to two recombinant proteins of Brugia spp. were studied. One molecule was the C-terminal portion of the filarial heat shock protein 70 (Bpa-26), representative of a cytoplasmic protein, and the second antigen was a single unit of the tandem repeats of a Brugia polypeptide (BpL-4), a secreted product which is prominently exposed to the immune system. Serum samples from 146 individuals resident in areas in which brugian filariasis is endemic were used, and it was found that whereas the levels of IgG1 and IgG3 responses to both Bpa-26 and BpL-4 were high, IgG4 and IgE antibodies to only BpL-4, not to Bpa-26, were prominent. Thus, an antigen which is chronically exposed to the immune system elicited a TH2-dependent isotype switch, as manifested by increased IgG4 and IgE responses. Moreover, IgG4 and IgE responses to BpL-4 showed a strong negative association, suggesting that mediators other than interleukin 4 must be responsible for such differential regulation of these two isotypes. When the data were analyzed as a function of clinical status, a striking association between elevated levels of IgG3 antibodies to Bpa-26 and manifestation of chronic obstructive disease was found; elephantiasis patients showed significantly higher levels of IgG3 antibodies to Bpa-26 than microfilaremics and asymptomatic amicrofilaremics. This indicates that an imbalance of isotypes of antibodies to particular filarial antigens might play a role in the pathogenesis of chronic disease.

Cytokine production in BALB/c mice immunized with radiation attenuated third stage larvae of the filarial nematode, Brugia pahangi

BALB/c mice immunized with radiation attenuated third stage larvae of the filarial nematode Brugia pahangi are strongly immune to challenge infection. Investigation of the profile of cytokines secreted by spleen cells from immune mice stimulated in vitro with either parasite Ag or with Con A revealed high levels of IL-5 and IL-9 and moderate levels of IL-4. In contrast, secretion of IFN-gamma by spleen cells from immune animals was negligible. Spleen cells from control mice secreted low levels of all cytokines assayed. Levels of parasite-specific IgE were significantly elevated in immune animals and a peripheral blood eosinophilia was observed, which exhibited a biphasic distribution. Our results are consistent with the preferential expansion of Th2 cells in immune animals and provide the basis for dissecting the means by which radiation attenuated larvae of filarial nematodes stimulate immunity.

Filariasis surveillance at the post-control stage in China

From 1956, when filariasis control was first listed in our national program, up to 1991, a cumulative total of 677,931,521 person-time blood examinations and 217,472,045 person-time diethylcarbamazine treatments were made in the whole country, and 835 (96.6%) out of the 864 endemic counties achieved the criterion for control of filariasis. Surveillance data collected in various provinces, autonomous regions and municipalities starting from the second year after they reached the criterion for control of filariasis demonstrated that in 1991 the microfilarial rate in human populations and natural infection of filarial larvae in mosquito vector populations in previous endemic areas had already declined to a very low level, even zero, without resurgence in quite a number of villages. In some places where filariasis was brought under control relatively early, the anti-filarial antibody positive rate of the human population has fallen to a level the same as or similar to that in nonendemic areas. Therefore, the data suggest that in most places where filariasis has been controlled, the transmission of bancroftian filariasis and periodic malayan filariasis has been interrupted. However, filariasis is still endemic in 29 counties in China at present, the danger of introduction of sources of infection by the floating population hasn't been extinguished yet, and there are still a few areas with weak links in filariasis control. Therefore, control work still needs to be strengthened and systematic surveillance must be pursued until the elimination of filariasis in the whole country.

Brugia pahangi: production of a monoclonal antibody reactive with the surface of infective larvae

Monoclonal antibodies against infective third-stage larvae (L3) of Brugia pahangi were generated from mice immunized with L3 antigens. The monoclonal antibodies were L3 stage-specific or stage-nonspecific. A BpG1 monoclonal antibody (IgG1 subclass) showing L3 stage-specificity was examined in detail. BpG1 recognized the surface of B. pahangi L3 and also reacted with the surface of Brugia malayi L3 but not with the surface of filarial worms of other genera, such as Acanthocheilonema viteae and Litomosoides carinii. BpG1 promoted cellular adhesion to the surface of B. pahangi L3. BpG1 bound on living L3 was shed but the shedding rate was relatively slow. The surface antigen recognized by BpG1 had a molecular weight of 58 kDa. It was stable to heat and periodate treatments but sensitive to trypsin digestion and was released from living L3 by SDS but not by Triton X-100 or CTAB. Preincubation of L3 with BpG1 significantly reduced the recovery rate of worms compared with the preincubation with a monoclonal antibody (IgG1 subclass) against the inner tissues of B. pahangi L3 or control supernatant of P3U1 myeloma cells. This result suggests that the antigen containing the BpG1 epitope may be one of the targets of a protective immune response against Brugia infection.

CD8+ T lymphocytes are not required for murine resistance to human filarial parasites

Mice are resistant to the establishment of infection with the nematode parasite Brugia malayi, an etiologic agent of human lymphatic filariasis. We have recently shown that T and B lymphocyte-deficient C.B.-17 scid/scid mice are permissive for infection with this parasite, whereas coisogenic C.B.-17+/+ mice are resistant. This observation suggests that T and B lymphocytes that comprise the antigen-specific immune system orchestrate murine resistance to B. malayi. In order to define the component of the antigen-specific immune response that is responsible for this resistance, we have tested the susceptibility of beta 2M-/- mice to infection with B. malayi L3 larvae. These mice are homozygous for insertional disruption of their B2m genes, which encode beta 2-microglobulin, the small subunit of the major histocompatibility (MHC) antigens. They do not express beta 2-microglobulin and, as a consequence, fail to express the class I major histocompatibility antigens, and they do not develop the CD8+ class I MHC-restricted cytotoxic T cell subset. We find that these mice are completely resistant to B. malayi, indicating that the CD8+ T lymphocyte subset is not an obligate requirement for murine resistance to human filarial parasites.

The Wellcome Trust Lecture. Infection and disease in lymphatic filariasis: an immunological perspective

The basic tenet of the immunological perspective of filarial disease is that differential immune responsiveness among individuals exposed to infection results in the different clinical manifestations that develop. The mechanisms involved in this differential responsiveness appear to reflect different T-cell cytokine response patterns. Asymptomatic patients with the clinically silent presentation of 'asymptomatic microfilaraemia', who have been previously described as being 'immunosuppressed' with respect to their generating pro-inflammatory (Th1-type) immune responses to parasite antigen, are now recognized to be fully responsive to parasite antigen but to produce cytokines and mediators that have primarily anti-inflammatory (Th2-like) effects. Studies with immunodeficient mice have indicated the existence of two alternative pathways to the development of lymphatic pathology: one dependent on the induction of inflammatory reactions by the host immune response, the other entirely independent of the immune system and reflecting the direct actions of the parasite or its products on the lymphatics. As histopathology of affected human lymphatics is consistent with this hypothesis, it may be that the lymphatic pathology seen normally in the amicrofilaraemic, highly immunoresponsive infected patients derives from inflammation induced by immune responses to parasite antigen, whereas the lymphatic pathology sometimes seen coexisting with the 'immunosuppressed' state of asymptomatic microfilaraemia actually reflects lymphatic damage that is not immunologically mediated. Though little information exists about the 'natural history' of lymphatic filariasis, there is no evidence for an inevitable progression from one clinical form to another.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of protective immunity to Brugia pahangi in jirds by drug-abbreviated infection

Protective immunity of homologous challenge infection was examined in jirds after drug-abbreviated infection with Brugia pahangi. Mebendazole (MBZ) treatment at the early prepatent (5-7 weeks of post infection) or the late prepatent (7-9 weeks of post infection) period was highly effective in causing almost complete eradication of the primary infection. After challenge infection, the worm burden was significantly reduced 19% (31.1 in average) and 77% (9.5) to that of the controls (38.8 and 41.7), respectively. The magnitude of eosinophil response paralleled the degree of protection. No or only a few microfilariae were seen after challenge infection in jirds treated during the prepatent periods. They were also resistant to intravenous challenge with the microfilariae of B. pahangi. MBZ treatment at the patent period was, on the contrary, incomplete against primarily infected adult worms, and was not able to induce either significant protection (30.1 vs 33.1 in control) or eosinophil response to the challenge infection.

Repeated infection of cats with Brugia pahangi: parasitological observations

Cats were repeatedly inoculated with infective larvae of Brugia pahangi. On parasitological grounds they could be divided into 5 groups. Group I--most cats (some 70%) became microfilaraemic (mf+) and retained high levels of microfilariae (mf) in their blood for over 2 years. In some Group I cats mf counts stabilized at high levels whilst in others mf counts continued to increase. Large numbers of fecund adult worms were recovered from their lymphatics. Adult counts were not made on the cats in the current experiments but over 100 adults have been recovered from 'super-susceptible' cats. Large amounts of B. pahangi adult antigen were consistently present in the serum of all Group I cats. About 30% of cats became amicrofilaraemic (mf-). In these cats the peak mf levels were seldom above 10,000 mf/ml. Group II--these cats had less than 10,000 mf/ml and low antigen levels. After more than 1 year of being repeatedly infected B. pahangi adult antigen slowly declined and eventually could no longer be detected in their serum and the number of mf declined very slowly after the fall in antigen levels. This shows that in Group II cats the adult worms die and as the cats are resistant to the development of the continuing weekly inoculation of L3 no new adults can develop. Group III--these cats became mf--during the first year of infection but remained B. pahangi antigen-positive for many weeks after this and, at autopsy, had living adults in their lymphatics.(ABSTRACT TRUNCATED AT 250 WORDS)

Brugia malayi: antibody responses to larval antigens in infected and immunized jirds

Vaccination with irradiated third stage Brugia malayi larvae (L3) has been reported to induce partial protective immunity to L3 challenge in jirds. The purpose of this study was to identify antigens that may be targets of protective immunity in this model. Jirds were immunized by s.c. injection of irradiated L3 and challenged either s.c. or i.p. Necropsy was performed 11 wk after challenge. Partial protection was achieved in s.c. challenged animals; worm recovery was only 41% of that observed in unvaccinated controls, and worms recovered from immunized animals were stunted. Worm recoveries in immunized animals that were challenged i.p. did not differ from those of unimmunized controls. Group differences in parasite antigen levels in sera collected 2-11 wk after larval challenge were consistent with parasitological findings obtained at necropsy. Antibody studies compared prechallenge sera from immunized animals to sera from infected (unimmunized) controls. Antibody responses to L3 surface antigens (assessed by IFA) were much stronger after immunization than after infection. Immunoblot studies showed preferential recognition of several L3 antigens (97, 54, 48, and 40 kDa) by antibodies in sera from immunized animals. Additional studies are needed to determine whether immunization with such preferentially recognized antigens can induce protection to larval challenge comparable to or better than that observed with live vaccines.

Immunologic tolerance in lymphatic filariasis. Diminished parasite-specific T and B lymphocyte precursor frequency in the microfilaremic state

To explore the mechanisms of antigen-specific immune unresponsiveness seen in microfilaremic patients with bancroftian filariasis, T and B cell precursor frequency analysis was performed using PBMC from individuals with either asymptomatic microfilaremia (MF, n = 7) or chronic lymphatic obstruction (CP, n = 20). Highly purified CD3+ cells were partially reconstituted with adherent cells and their proliferative response to parasite antigens determined in cultures of T cells by limiting dilution analysis. A filter immunoplaque assay also assessed the frequency of both total and parasite-specific Ig-producing B cells. While the lymphocyte proliferation to mitogens and to a nonparasite antigen (Streptolysin-O, [SLO]) were similar in all groups of patients, the frequency of parasite-specific CD3+ T cells was significantly lower (geometric mean [GM], 1/3,757) in MF patients when compared to that in CP patients (GM 1/1,513; P less than 0.001). Similarly, the proportion of lymphocytes producing parasite-specific IgE or IgG was significantly lower in MF patients (IgE mean, 0.2%; IgG mean, 0.33%) compared with CP patients (IgE mean, 3.2%; IgG mean, 1.76%; P less than 0.05 for both comparisons). These observations imply that low numbers of parasite-specific T and B lymphocytes may be partially responsible for the severely diminished capacity of lymphocytes from patients with MF to produce parasite-specific antibody and to proliferate to parasite antigen in vitro. Such differences in parasite-specific lymphocyte responses suggest that tolerance by clonal anergy may be a critical mechanism for maintaining the microfilaremic state.

Surface-associated antigens of Brugia malayi L2 and L3 parasites during vector-stage development

Surface and metabolic labeling procedures were used to characterize the composition and the time of expression of Brugia malayi L2 and L3 surface-associated molecules as the larvae develop within the mosquito vector. Larvae were harvested from mosquito tissues at 5 (early L2), 8 (late L2) and 11 (L3) days post-infection and labeled with 125I-Iodo-Gen. The results of one-dimensional analysis showed that there is a progressive increase in the complexity of peptides associated with the surface of developing larvae, culminating in the expression of 7 major labeled components on L3s. Both L2 and L3 parasites have surface-associated components of 42, 35, 33, 19 and 17 kDa. Between days 8 and 11 of development in the insect vector, Brugia malayi undergoes the L2 to L3 molt and acquires additional major immunogenic peptides of 40 and 22 kDa. Two-dimensional analyses of extracts from 125I-labeled L2s and L3s revealed that the major 35-, 33-, 19- and 17-kDa molecules are part of a peptide complex that forms a 'ladder' between 17 and 150 kDa. To gain information on the times during which the major surface-associated molecules are produced by the parasite, larvae were labeled with [35S]methionine either in situ as they developed within the mosquito or during culture after exiting the vector. For in situ labeling, [35S]methionine was introduced into the hemolymph of infected mosquitoes by micro-injection at days 2, 5 and 8 post-infection and the larvae were allowed to develop for an additional 3 days. The results of 1- and 2-dimensional analyses of [35S]methionine-labeled extracts from vector-stage or post-vector-stage larvae indicate that the molecules associated with the surface of B. malayi L3s are synthesized between day 5 and day 11 of development in the insect host. Immediately after the larvae exit the vector, the synthesis of the 40 and 22-kDa peptides is drastically reduced or terminated.

Cats with single Brugia pahangi infections: relationship between parasitological status and humoral responses to somatic and surface parasite antigens

Cats given a single inoculation of Brugia pahangi infective larvae (L3) were retrospectively allocated into three groups according to parasitological outcome of infection. Recognition of somatic and surface antigens of B. pahangi by sera from each group was compared by ELISA, immunoelectroblotting, and immunoprecipitation techniques. In cats that never became microfilaraemic mean serum IgG antibody levels against somatic extracts from adult male worms, L3, and microfilariae (mf) were higher than levels in cats that initially became microfilaraemic (mf + ve) then spontaneously became nonmicrofilaraemic (mf - ve). The lowest levels of antibody against each stage were found in cats that remained persistently mf + ve. Antigenic components of 18 kD and 22 kD in somatic extracts of adult worms and L3 were recognized by sera from cats that never became mf + ve and by spontaneously mf - ve cats, but not by sera of persistently mf + ve cats. When radioiodinated surface antigens of mixed adult worms and microfilariae were immunoprecipitated by sera from cats in the three groups, no correlation was observed between recognition of individual antigen components and parasitological outcome of infection.

Brugia pahangi: effects of maternal filariasis on the responses of their progeny to homologous challenge infection

Granulomatous lesion formation and immune responses to Brugia pahangi infections were compared in age-matched male progeny of homologously infected and uninfected female jirds. Infections initiated in 2-week-old offspring yielded mean +/- SD adult worm recoveries of 6.0 +/- 5.7 and 4.2 +/- 5.4 in offspring from infected or uninfected mothers, respectively. Infections initiated in 4-week-old offspring resulted in an mean +/- SD recovery of adult worms of 11.3 +/- 11.3 and 10.2 +/- 5.8 in offspring from infected and uninfected mothers, respectively. The ratio of intralymphatic thrombi per intralymphatic worm was similar between infected offspring from infected or uninfected mothers within experiments. Areas of granulomas around B. pahangi antigen-coated beads embolized in the lungs were not significantly affected by maternal origin in infected or uninfected progeny. Offspring infected at 2 or 4 weeks of age from infected mothers exhibited significantly reduced titers of serum IgG antibodies to Brugia antigens at 5-8 weeks postinfection compared to infected offspring of uninfected mothers. Infected offspring from infected mothers also had significantly fewer splenic IgG plaque-forming cells to B. pahangi antigens at 5 weeks postinfection than similarly infected offspring from uninfected mothers. Western immunoblot analysis indicated qualitative and quantitative reductions in serum antibody reactivity to adult B. pahangi antigens in infected progeny of infected females compared to age-matched infected controls. Reduced homologous serum antibody responses in progeny exposed to maternal B. pahangi infection suggest that maternal immunoregulation to filarial antigens may occur. Reduced antibody responsiveness to B. pahangi antigens observed in infected offspring from infected mothers, however, had no demonstrable effect on adult worm burdens, microfilaremias, lymphatic lesion formation, or antigen-specific granulomatous inflammatory responses compared to infected progeny of uninfected mothers.

Release of prostaglandin E2 by microfilariae of Wuchereria bancrofti and Brugia malayi

To elucidate the local release of immunomodulatory prostaglandins by intravascular filarial parasites, the formation of prostaglandin E2 (PGE2) was examined in individual microfilariae of Wuchereria bancrofti and Brugia malayi. Following incubation of living microfilariae immobilized in an agar matrix, prostaglandins released by the parasites were fixed by carbodiimide and localized by indirect immunofluorescence. Prostaglandin E2 was specifically detected around the entire surface of microfilariae with anti-PGE2 antiserum, but not with control nonimmune or PGE2 affinity-immunoadsorbed antiserum. These results provide direct evidence that individual microfilariae of W. bancrofti as well as B. malayi release prostaglandins into their microenvironment. The release of PGE2 by these intravascular parasites may modulate host leukocyte responses, and thereby contribute to the immune defects observed in infected humans with peripheral microfilaremia.

Transmission-blocking antibodies recognize microfilarial chitinase in brugian lymphatic filariasis

Brugia malayi is a parasitic nematode that causes lymphatic filariasis in humans. The monoclonal antibody MF1, which mediates clearance of peripheral microfilaremia in a gerbil infection model, recognizes two stage-specific proteins, p70 and p75, in B. malayi microfilariae. cDNA coding for the MF1 antigen was sequenced, and the predicted protein sequence shows significant similarities to chitinases from bacteria and yeast. When microfilarial extracts and purified preparations of the MF1 antigen were tested for chitinase activity, strong bands of chitin-degrading activity comigrated in SDS/PAGE with p70 and p75 and showed a reduction-dependent mobility shift characteristic of the MF1 antigen. Thus, the MF1 antigen is microfilarial chitinase, which may function to degrade chitin-containing structures in the microfilaria or in its mosquito vector during parasite development and transmission.

Tropical pulmonary eosinophilia

Tropical pulmonary eosinophilia is one of the many PIE syndromes [pulmonary infiltrates with eosinophilia (of the peripheral blood)]. It is caused by immunologic hyperresponsiveness to the filarial parasites Wuchereria bancrofti or Brugia malayi. Its clinical presentation includes nocturnal cough, dyspnea, wheezing, fever, weight loss, fatigue, interstitial mottling on chest radiograph, predominantly restrictive but also obstructive lung function abnormalities, and peripheral blood eosinophilia of more than 3000 per microliter. It can be distinguished from other PIE syndromes by the patient's history of residence in the tropics, by the presence of extraordinarily high levels of both serum IgE and antifilarial antibodies, and by the dramatic clinical improvement after treatment with the antifilarial drug diethylcarbamazine. Recent studies indicate that the compromised lung diffusion capacity of patients with acute tropical pulmonary eosinophilia is a function of the degree of the eosinophilic alveolitis present and that, despite a 3-week course of diethylcarbamazine, low-grade alveolitis persists in almost half of such patients; this persistent alveolitis is likely to be the cause of the progressive interstitial fibrosis seen in many untreated or inadequately treated patients with tropical pulmonary eosinophilia.

Brugia malayi: patterns of expression of surface-associated antigens

Patterns of expression of surface-associated antigens were analyzed in the filarial nematode Brugia malayi immediately prior, and during development in the vertebrate host. Two surface-associated protein molecules, i.e., accessible to surface radioiodination and soluble in aqueous buffers, were investigated: Mrs 29-30,000 and 16,000, both of which are antigenic in infected animals. The Mr 29-30,000 glycoprotein is expressed in a surface-associated manner by adult worms and by fourth-stage larvae, but is not detectable in preparasitic third-stage larvae. The 16,000 component, which appears not to be glycosylated, is surface-associated in adult worms and fourth-stage larvae. In contrast to the 29-30,000 glycoprotein, the 16,000 protein is also expressed both by pre- and postparastic third-stage larvae. However, it becomes surface-associated only after infection. Thus, immediately prior, and during development within the vertebrate host, B. malayi displays at least two different patterns of expression of surface-associated antigens: (i) de novo, intiated either immediately after infection (phase specific) or during genesis of the fourth-stage larva (stage specific); (ii) continuous, but with phase-dependent surface exposure of previously cryptic antigens, during the transition from intermediate to definitive host.

Effect of carrageenan on the resistance of congenitally athymic nude and normal BALB/c mice to infective larvae of Brugia malayi

Resistance of BALB/c mice to infective third-stage larvae (L3) of the human filarial parasite Brugia malayi is thymus-dependent, although the actual effector mechanisms that mediate larval killing are unknown. The present study examined the effect of carrageenan (CGN) on the mechanisms of resistance to B. malayi infection in heterozygous (nu/+) and nude (nu/nu) mice. Mice were treated with CGN at a single dose of 20 or 200 mg/kg and were inoculated intraperitoneally 1 day later with 100 L3. The results showed a dose-dependent increase in the numbers of L4 and L5 that were recovered from nu/+ and nu/nu mice. CGN treatment also enhanced the recovery of mature adult worms from nu/nu mice and appeared to abolish partially the dichotomy of resistance between the usually more susceptible male and the more resistant female nu/nu mouse. Microfilariae were found in the peripheral blood and the peritoneal cavity of CGN-treated male and female nu/nu mice and in the peritoneal cavity of male but not female nu/+ mice. Fewer larval granulomas were recovered from the peritoneal cavity of treated mice. CGN-treated, parasitized nu/+ and nu/nu mice showed high titers of IgM and IgG antibodies. An experimental compound, CGP 20376, showed 100% larvicidal activity following the administration of a single dose of 20 mg/kg to CGN-treated mice. From this study, we conclude that macrophages alone or in conjunction with other cells are actively involved in the resistance of mice to B. malayi L3.

Identification of paramyosin as a potential protective antigen against Brugia malayi infection in jirds

Vaccination of jirds with irradiated infective larvae of Brugia malayi has been reported to provide partial immunity to larval challenge. In the present study, we found that sera from vaccinated animals recognized larval antigens with apparent molecular weights of 97, 55-60, and 10 kDa that were not recognized by sera from infected animals. A B. malayi cDNA expression library in lambda gt11 was screened to identify clones that were preferentially recognized by sera from immunized animals. One of these clones (BM-5) was chosen for further study. BM-5 contains a 2.1 kb DNA insert and produces a fusion protein with a molecular weight of 185 kDa. Antibody, affinity-purified with the BM-5 fusion protein, binds to a 97 kDa native B. malayi antigen. Immunological studies and partial DNA sequence data confirm that BM-5 encodes paramyosin. Recombinant B. malayi paramyosin is strongly recognized by antibodies in sera from jirds that have been immunized either by injection with irradiated larvae or by chemotherapy-abbreviated infection. Most sera from infected jirds do not contain antibody to paramyosin. Additional studies are needed to determine whether paramyosin is actually protective in this filariasis model.

Qualitative characterization of antibody responses to single and multiple Brugia pahangi infections in jirds

Antibody responses of jirds, singly and multiply inoculated with Brugia pahangi infective larvae (L3), to soluble somatic extracts of adult parasites were characterized by western blot analysis. Forty-two protein bands ranging in molecular weight from 12 to 160 kDa were recognized by sera from infected jirds. Antibody recognition of individual B. pahangi antigen bands in this assay appears to be independent of antibody enzyme-linked immunosorbent assay (ELISA) titers to crude parasite extract, severity of lymphatic lesions, levels of microfilaremia, numbers of L3 inoculated, or numbers of adult parasites in individual jirds. Antibody recognition of protein bands with molecular weights of 37 kDa, 21 kDa, and 17 kDa, however, did temporally correspond with certain parasitological and pathologic events. Antibody against the 37-kDa protein band first was identified at the onset of patency, reaching a 90% prevalence rate by 90 days postinfection (DPI). The prevalence of this antibody remained high. Antibody recognition of the 21-kDa protein band first occurred at 90 DPI and gradually increased in prevalence during the course of infection temporally similar to the increase in microfilaremia. Recognition of the 17-kDa protein band first occurred at 48 DPI, reached a maximum prevalence of 80% at 90 DPI, and decreased to a minimal prevalence by 160 DPI. Prevalence of antibody responses to the 17-kDa protein band corresponded temporally with the kinetics of the rise and fall of numbers of intralymphatic thrombi. The patterns of antibody response to these 3 bands were similar in both singly and multiply inoculated animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Antifilarial cellular responses detected in a Haitian pediatric population by use of a microblastogenesis assay

Previous reports have demonstrated age-related shifts in antifilarial humoral immune responses in 6- to 10-year-old Haitian children; the responses consisted of elevated parasite-specific IgG2 and IgG3 in amicrofilaremic children and elevated IgG4 in microfilaremic children. In this study, the cell-mediated immune responses to soluble adult and microfilarial extracts of Brugia pahangi, determined by use of a microblastogenesis assay, were examined. Capillary blood samples were collected by finger prick from 176 Haitian children in an area with endemic Wuchereria bancrofti. Antigen-specific cellular responsiveness varied as a function of infection status but not age or sex; amicrofilaremic children had significantly greater responses to adult antigens than did microfilaremic children. Significant responses were detected in children less than 2 years of age; thus, correlations observed between filarial antigen-specific responses and infection status are established early in life.

Inhibition of antigen-driven proliferative responses and enhancement of antibody production during infection with Brugia pahangi

Long standing Brugia pahangi infections in seven dogs, restricted to one rear limb popliteal lymph node and its afferent ducts, were monitored with regard to proliferative responses and antibody production specific for a PBS extract of B. pahangi (BpA) by cells from infected and uninfected lymph nodes and by PBL. Five of 10 dogs were negative for proliferative responses to BpA in node cells from infected limbs, yet they had positive PBL responses, and another was negative in both node cells and PBL. Production of BpA-specific antibody was detected in cultures of node cells from infected limbs of 9 of 10 dogs, but only in two cultures of node cells from uninfected limbs and not at all in PBL cultures. Three dogs with responsive node cells produced the least amount of anti-BpA antibody in culture. Injections of B. pahangi adult worm excretory/secretory products (ES), totaling 1 mg over 48 h, into the limb of the original infections in seven dogs, resulted in inhibition of Ag-driven proliferation by cell populations previously responsive to BpA. There was a loss of PBL responsiveness by all but one infected dog and a loss of node cell response by the two dogs previously responsive in infected and uninfected nodes. This loss of responsiveness lasted at least 28 days in three dogs. There was no evidence of suppression of responses to mitogens either before or after ES injection. In contrast, BpA-specific antibody production was greatly increased in node cells from infected limbs injected with ES. Similar injections into the uninfected limbs of two infected dogs produced no change of proliferative responses or of antibody production in the uninfected node. These results indicate that ES can modulate immune cell, Ag-driven proliferation, and simultaneously enhance antibody production in previously infected nodes. This may promote parasite survival by inhibiting cellular attack based on delayed-type hypersensitivity while directing immune responses toward production of antibodies that are less damaging to the adult helminth.

Circulating filarial antigen in cats infected with Brugia pahangi is indicative of the presence of adult worms

Using counterimmunoelectrophoresis with rabbit antisera raised against soluble extracts of adult females of Brugia pahangi parasite antigen was detected in the serum of all cats repeatedly infected with B. pahangi. Antigen was never detected in uninfected cats. The antigen was associated with the presence of adult worms. Antigen was detected consistently in a cat that was amicrofilaraemic but at autopsy harboured only two or three adult worms. Conversely, some cats showed slowly declining numbers of microfilariae and, in these, circulating antigen declined before the number of microfilariae. Eventually no antigen was detectable in circulation whereas microfilariae, although in diminishing numbers, were still present. At autopsy no adult worms were found in these cats. Antigen also appeared in several cats before they became microfilaraemic.

Monitoring of filarial antigens in jirds and patients after treatment

We developed a sandwich ELISA with monoclonal antibodies to monitor filarial antigens in animals and patients after infection and treatment. Levels of antimicrofilarial antibodies and parasite antigens were measured periodically in 40 B. malayi infected jirds. In all animals L3 HC11 antigen was detected earlier than Mf ES34 antigen, while antimicrofilarial antibodies appeared much more slowly. These serologic changes precede the onset of patent infections. After 3 courses of treatment with DEC and M170, the levels of parasite antigen in sera and of Mf in peritoneal cavities were monitored in 23 infected jirds. In 8 jirds Mf became negative, no adult worms were found in 7 jirds and a single degenerating female worm was present in 1 jird. ES34 and HC11 were undetectable in 8/8 and 6/8 necropsy sera. Mf persisted in 11 animals, 9 jirds were necropsied, 8 contained adult worms. Detectable levels of ES34 or HC11 antigen were present in 7/9 and 8/9 from these animals. In sham-treatment, few changes were noted in control animals. Thus, parasitological findings at necropsy are correlated with the results of antigen detection assay. We analyzed serial serum samples from 32 bancroftian microfilaremia collected 1-42 months after DEC therapy. Mf resolved rapidly in all treated individuals. ES34 disappeared faster than HC11, 3 months after treatment. Levels of ES34 and HC11 antigens remained detectable or rising after treatment in 8 and 10 individuals. Four patients' Mf recurred 20-42 months after treatment. These findings show that the remaining or a rise in serum levels of antigen after therapy predicts recurrent microfilaremia in patients and additional treatment is needed.

Effect of CGP 20376 on Brugia malayi and parasite antigenemia in jirds

This study was designed to investigate the activity of CGP 20376, a benzothiazole derivative, against Brugia malayi in jirds and to illustrate the utility of parasite antigen detection as a means of monitoring drug efficacy in filariasis. Drug treatment was 100% effective in jirds treated 3 or 24 days after infection. Microfilaria and adult worm counts were reduced (relative to counts in sham-treated control animals) by 96% and 95%, respectively, in animals treated 153 days after infection. Four of 6 animals in this treatment group cleared their microfilaremias and were free of adult worms 5 mo after treatment. Thus, CGP 20376 was effective against all life cycle stages of B. malayi in jirds. Parasite antigen levels in jird sera were consistent with parasitological results in all treatment groups, but antigen clearance was incomplete in some cases after apparently successful treatment of mature and immature infections.

Brugia pahangi: circulating antibodies to adult worm antigens in uninfected progeny of homologously infected female jirds

Serum IgG antibody levels to adult Brugia pahangi antigens were measured in uninfected offspring from uninfected and B. pahangi-infected female jirds. Antibody titers to B. pahangi antigens in sera of offspring from infected females mimicked the maternal titer during the suckling period. Neonate titers peaked at 2 weeks of age at levels as high as 1:4100, then decreased to levels well below maternal titers by 8-12 weeks of age. Concurrent maternal and 2-week-old neonate sera recognized identical B. pahangi antigens in Western blots. Spleen cells from 2-week-old filariae-exposed and unexposed offspring failed to produce measurable antibody to B. pahangi in vitro. Progeny of uninfected mothers nursed by B. pahangi-infected females showed circulating IgG antibody titers to adult worm antigens similar to those of homologously reared offspring. Conversely, offspring born to B. pahangi-infected females and nursed by an uninfected female had no serum antibodies to B. pahangi antigens. Blastogenic responses of spleen cells to the mitogens phytohemagglutinin and pokeweed mitogen, and adult B. pahangi antigens, were not different between offspring groups. Mean areas of pulmonary granulomas induced by the intravenous inoculation of B. pahangi antigen-coated beads also did not differ between 4- and 8-week-old progeny of uninfected or infected females. These results suggest that the circulating IgG antibodies to adult B. pahangi antigens demonstrated in offspring of infected female jirds are maternally derived via the milk and do not alter the cellular responses of uninfected offspring to B. pahangi antigens as measured by antigen-stimulated blastogenesis or pulmonary granulomatous inflammatory response.

Variations in complement activation of Brugia patei, B. malayi and B. pahangi microfilariae

The complement of fresh normal heterozygotic BALB/C (nu/+) and nude (nu/nu) mice was activated by sheathed microfilariae (Mf) of Brugia malayi and B. pahangi but not by B. patei. Mouse C3 was detected by immunofluorescence on the sheathed surface of B. malayi and B. pahangi Mf but not on B. patei Mf. The bound complement promoted macrophage and neutrophil mediated adherence and cytotoxicity to these Mf. However, BALB/C nu/+ or nu/nu mouse macrophages and neutrophils adhered to exsheathed Mf of B. patei and killed them in the presence of fresh normal mouse serum (NMS). C3 molecules were detected on the cuticle of exsheathed Mf of B. patei and B. malayi. Fresh NMS (nu/+ or nu/nu) depleted of complement factors by heating or by zymosan or anti-mouse C3, failed to promote cell adherence to these parasites. EDTA but not EGTA abolished the adherence activity to sheathed and exsheathed Mf of B. malayi, whereas both EGTA and EDTA abolished the adherence activity to exsheathed Mf of B. patei and sheathed Mf of B. pahangi suggesting the different pathways of complement activation by these closely related species. Macrophages and neutrophils from peritoneal exudate cells of nu/+ or nu/nu were equally potent in adherence and killing of Mf. Transfused B. patei but not B. malayi or B. pahangi Mf were recovered from the peritoneal cavity of BALB/C mice with no cell adherence and cytotoxicity.

Monoclonal antibodies to secreted antigens of Brugia malayi define a cross-reactive non-phosphocholine determinant on helminth parasites

The excretory-secretory (ES) antigens of the filarial parasite Brugia malayi adult (BmA) and microfilariae (MF) were analysed for differences in their protein composition by two-dimensional gel electrophoresis. Both BmA and MF biosynthetically labelled with [3H]-leucine released a 200 kD molecule with pI (isoelectric point) ranging from 5.1 to 6.8. A monoclonal antibody (MoAb) to phosphocholine (PC) immunoprecipitated the 200 kD molecule with a PI of 5.1-5.3 from both BmA and MF. Immunization of CBA/N mice with ES antigens resulted in MoAb that reacted with PC, as well as some that did not (ES-1, ES-2 and ES-3). The epitopes recognized by these non-PC MoAb varied greatly in their molecular weight, heat-resistance, TCA-solubility and metaperiodate-sensitivity, which suggests a proteoglycan nature of the epitope. An antigen capture assay using ES-1 and ES-3 detected a circulating filarial antigen not only in patients infected with Wuchereria bancrofti (77-83% of those with asymptomatic microfilaraemia and 52-60% of those with chronic lymphatic obstruction) but also in serum from patients infected with other helminth parasites (12-100%). Indeed, the epitope recognized by these MoAb was also present on other helminth parasites, which suggests conservation of a carbohydrate-like prosthetic group(s) on diverse helminth species.

Quantitative cellular cytotoxicity to Brugia malayi microfilariae: in vitro studies of sera from an area endemic for filariasis in Andhra Pradesh, India

The extent of eosinophil and neutrophil cell-mediated cytotoxicity on Brugia malayi microfilariae by sera from an area endemic for bancroftian filariasis in Andhra Pradesh, India, has been studied in vitro in terms of the clinical status of the subjects. At physical examination, 66 serum samples were collected. Group "A" included patients with various disease manifestations like lymphoedema, hydrocoele, lymphangitis and elephantiasis. Group "B" had microfilaraemia ranging from 1-300/ml of blood. Subjects with no history of infection past or present (endemic normals) were studied as Group "C". Out of 38 sera tested individually with eosinophils, 14/18 of Group A, 10/11 of Group B and 7/9 of Group C promoted higher (21-97%), moderate (18-88%) and highest (51-95%) range of cytotoxicity, respectively. The age, clinical status and duration of disease among the infected subjects appeared to correlate with the microfilarial mortality. In Group B, we observed the highest microfilarial count (16-300/ml) in lower (1-20 yrs) age groups. These individuals promoted higher (77-83%) cytotoxicity compared to the older age group (21-40 or 41-60) with low (1-36/ml) microfilaraemia. Group C sera were highly toxic to microfilariae. All those that were positive promoted greater than 50% mortality. Eighteen nonendemic normal sera had no effect on microfilariae. The overlapping but differential toxicity of the sera indicates that various clinical manifestations are associated with different types of cellular and humoral responses. These studies should help focus identification of the target epitopes of various immune responses of the host.

Analysis of isotype-specific antifilarial antibody levels in a Haitian pediatric population

Previous studies of antifilarial antibodies in a pediatric population residing in an area with endemic Wuchereria bancrofti filariasis have demonstrated age related shifts in antifilarial immunity. To further characterize humoral responses in Haitian children, serum samples from 129 patients (3 months-15 years of age) were analyzed by ELISA for isotype-specific antifilarial antibody responses. Age-stratified analysis of geometric mean antibody titers showed significant increases in antibody titers of all isotypes with age in the amicrofilaremic population. Antifilarial IgG1, 2, and 3 levels were higher in amicrofilaremic children than in microfilaremic children, significantly so for IgG2 and IgG3. In contrast, IgG4 antibody levels were higher in microfilaremic subjects than in amicrofilaremic subjects. A multivariate, unconditional, logistic regression model was developed from these data to predict infection status. The model correctly classified 91.6% of the amicrofilaremic subjects, but only 55.6% of the microfilaremic subjects.

Onchocerca volvulus, O. gutturosa, Brugia malayi, and Dirofilaria immitis: a comparative study of the immunochemical properties of cuticular proteins from filarial parasites

We compared the chemical and immunological properties of cuticular collagens from four species of filarial nematodes, Onchocerca volvulus, O. gutturosa, Brugia malayi, and Dirofilaria immitis. The electrophoretic mobility of the major polypeptides extracted from adult worms is characteristic for each species studied. Cuticular collagens from adult worms and infective larvae differ in their susceptibility to proteases that cleave vertebrate collagens and to collagenases prepared from different developmental stages of filarial parasites. The overall amino acid composition of filarial collagens resembles that of vertebrate interstitial collagens and differs from that reported for collagens from free-living or intestinal nematodes. However, cuticular proteins of the four filarial species studied significantly differed in amino acid composition and in their reactivity with antisera to interstitial and basement membrane collagens of vertebrates.

Humoral immune response to infective larval antigen in Brugia malayi infected Mastomys natalensis

The sequential changes in the humoral immune response against infective larval antigens during the course of Brugia malayi infection in Mastomys natalensis have been studied using enzyme linked immunosorbent assay. IgM antibody against B. malayi infective larval excretory secretory (ES) antigen was detected in the peripheral circulation within a week of infection, whereas IgM antibody against B. malayi infective larval somatic antigen and IgG antibody against both somatic and ES antigens were detected on day 20 post-inoculation. Thereafter, the antibody levels showed a steady increase until day 150. A gradual decrease of IgM antibody level was observed upto day 360, whereas IgG antibody level was decreased upto day 250 and then maintained almost the same level upto day 360. Wuchereria bancrofti cross reactive antigen as well as B. malayi infective larval ES antigen were detected in blood circulation on day 20, the level increased upto day 150 and then remained almost the same upto day 360 with slight variations. Studies of antigen and antibody levels in microfilaraemic and amicrofilaraemic animals show that there is no significant difference in antibody level whereas elevated antigen titre was observed in active infection with microfilaraemia.

[Advances in filariasis control and research in China during 1986-1990. National Technical Steering Group for Filariasis Control and Research, MOPH]

Based upon the statistical data during 1986-1990 from provincial, regional or municipal institutions involved in the control and research of filariasis, important achievement in filariasis control has been achieved since 1986. During the 5 years, 22,350,772 person were blood-examined, among them, 268,034 were found to be microfilaria positive; a total of 78,550,945 man/times of treatment with DEC were given (including administration of DEC-medicated salt). Till the end of 1990, filariasis has been basically eliminated in 823 counties/cities out of the 864 endemic counties/cities, and has been basically eliminated in 12 endemic provinces, one autonomous region and one municipality. Thus far, filariasis is still prevalent in 41 counties/cities of Anhui province. Parasitological, serological and entomological monitoring on filariasis is being executed according to the "Technical scheme for filariasis surveillance in areas where the disease has been basically eliminated" formulated by the Ministry of Public Health. The preliminary results of longitudinal surveillance indicated that the decline of microfilaremia rate and the absence of resurgence coincided with the decrease in antibody titre in the population by IFAT. The progress of research work dealing with the transmission potential in areas where filariasis had been under control, the methods of immunodiagnosis and the treatment of patients with clinical signs was also reviewed.

The expression of the Mr 30,000 antigen in the third stage larvae of Brugia pahangi

The expression of the Mr 30,000 surface antigen in the third stage larvae (L3) of Brugia pahangi has been investigated. The antigen could be detected only with great difficulty in the mosquito derived L3 externally labelled with 125I but was more easily labelled in 24 and 48 h post-infective larvae harvested from the vertebrate host. Labelling of a detergent extract of mosquito derived L3 with 125I demonstrated that the Mr 30,000 antigen was indeed present in this life cycle stage, presumably in an internal localization. It seems likely that the Mr 30,000 antigen is not fully expressed in the parasite cuticle until after infection of the vertebrate host. The data presented also suggest that there are major differences in the surface properties of the mosquito derived L3 compared to the p.i. L3 harvested from the vertebrate host.