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.