Description, mechanisms and control of reactions to treatment in the human filariases

Since diethylcarbamazine at the dosages used to treat filarial infections has little direct toxicity, most of the post-treatment reactions (termed Mazzotti reactions in onchocerciasis) result from the immunological inflammatory mechanisms activated in the process of clearing and killing the skin-swelling or blood-borne microfilariae. These reactions may be either localized to the skin, eyes or lymphatics or generalized systemically (e.g. headache, fever, adenopathy, arthralgia, tachypnoea, tachycardia, hypotension and even death). The occurrence and intensity of such reactions can be shown to be related to the intensity of infection. It had previously been speculated that the best candidates for triggering these post-treatment reactions were activation of complement, immediate hypersensitivity responses mediated by immunoglobulin E, and degranulation of eosinophils with resultant inflammatory reactivity. Recent detailed studies have given little support to the primacy of either complement or immediate hypersensitivity responses in triggering such reactions, but eosinophil degranulation with the release of inflammatory mediators into the tissues and peripheral blood is extremely prominent in all patients undergoing post-treatment reactions and develops with a time course generally consistent with what would be required of an initiator of such reactions. Other inflammatory mediators and pathways may be involved (e.g. kinins, prostaglandins, immune complexes, leukotrienes, platelets and parasite-derived inflammatory molecules), but there is currently no evidence to implicate any of these mechanisms as initiators of the response. Symptomatic treatment of these post-treatment reactions with analgesics, antipyretics, antihypotensive agents etc. has been successful, but their prevention has been achieved only with the broadly anti-inflammatory corticosteroids.

Development and standardization of a rapid, PCR-based method for the detection of Wuchereria bancrofti in mosquitoes, for xenomonitoring the human prevalence of bancroftian filariasis

PCR has recently been studied as a promising tool for monitoring the progress of efforts to eliminate lymphatic filariasis. PCR can be used to test concurrently at least 30 pools, with as many as 40 mosquitoes in each pool, for the presence of filarial larvae. The SspI PCR assay for the detection of Wuchereria bancrofti DNA in pools of mosquitoes has been used since 1994 in a variety of laboratories worldwide. During that time, the original assay has been modified in these different laboratories and no standardized assay currently exists. In an effort to standardize and improve the assay, a meeting was held on 15-16 November 2001, at Emory University in Atlanta, with representatives from most of the laboratories currently using the assay. The first round of testing was designed to test the four most promising methods for DNA extraction from pools of mosquitoes. Two of the four methods stood out as clearly the best and these will be now optimised and evaluated in two further rounds of testing.

Xenomonitoring of Culex quinquefasciatus mosquitoes as a guide for detecting the presence or absence of lymphatic filariasis: a preliminary protocol for mosquito sampling

A protocol for the collection of resting, blood-engorged Culex quinquefasciatus Say and their examination for microfilariae has been developed as a way of detecting whether lymphatic filariasis (LF) occurs in a particular locality. The protocol was first implemented in a pilot study in Trinidad, West Indies. For gathering prevalence data, such xenomonitoring is a suitable alternative to the use of human bait, which is ethically questionable. The resting mosquitoes were collected, either indoors or outdoors, using electrical and mouth aspirators. A 'cocoeya broom', made from a bunch of the midribs of coconut-palm leaves, was found to be useful in flushing out the mosquitoes resting in hard-to-reach areas within bedrooms. The rationale behind the strategy and the five-step methodology, of householder notification, mapping, preparation of equipment, mosquito collecting and laboratory processing, are described. Data from the pilot study indicate that this xenomonitoring protocol may be applicable worldwide, albeit with modifications to take account of variations in the vector species involved and their ecology and resting behaviour.

Worm burden and host responsiveness in Wuchereria bancrofti infection: use of antigen detection to refine earlier assessments from the South Pacific

A population from the Wuchereria bancrofti-endemic island of Mauke was reevaluated retrospectively by use of the Og4C3 circulating antigen (CAg) enzyme-linked immunosorbent assay to assess active infection in relation to host responses by age and gender. Use of microfilaremia (Mf) alone misclassified approximately 50% of infected people, although CAg and Mf levels were positively correlated. Levels of CAg peaked between those aged 31-60 years; men aged > 60 years had a significantly higher CAg prevalence (> 90%) than women. Filaria-specific immunoglobulin (Ig) G4 reached maximum levels in both genders at age 51-60 years. By analysis of variance, both age and gender significantly influenced CAg and IgG4, with men having higher levels of both in the total population. Individuals positive for CAg had significantly lower lymphocyte proliferation responses to parasite antigen than did CAg-negative people, regardless of clinical status. This study reemphasizes the importance of CAg measurements for accurately assessing filarial prevalence and clinical status and demonstrates the relationship between active infection and immune responsiveness.

Lymphatic filariasis in children: adenopathy and its evolution in two young girls

Lymphatic filariasis is a widespread infectious disease of children in endemic areas, but little is known about the early lymphatic damage in children and its evolution, either with or without treatment. Two girls (ages 6 and 12 years) from a Wuchereria bancrofti endemic region of Brazil presented with chronic inguinal adenopathy. Neither had microfilaremia. By ultrasound both were shown to have living adult worms in their enlarged inguinal nodes and had occult local lymphatic damage (lymphangiectasis). One girl spontaneously developed acute adenitis in the affected node prior to any intervention; this adenitis resolved within 10 days and was associated with the progressive disappearance over 45-90 days of all local abnormalities detectable by ultrasound. In the other child, after treatment with a single dose of diethylcarbamazine (DEC), the same clinical picture of transient adenitis and resolving abnormalities (detectable by ultrasound) occurred. These findings demonstrated filariasis as the cause of adenopathy in children, and also both spontaneous and treatment-induced worm-death, with subsequent reversal of lymphatic abnormalities.

Lymphatic filariasis: an infection of childhood

Lymphatic filariasis (LF), already recognized as a widespread, seriously handicapping disease of adults, was generally thought to occur only sporadically in children. New, highly sensitive diagnostic tests (antigen detection, ultrasound examination) now reveal, however, that LF is first acquired in childhood, often with as many as one-third of children infected before age 5. Initial damage to the lymphatic system by the parasites generally remains subclinical for years or gives rise only to non-specific presentations of adenitis/adenopathy; however, especially after puberty the characteristic clinical features of the adult disease syndromes (lymphoedema, hydrocoele) manifest themselves. Recognizing that LF disease starts its development in childhood has immediate practical implications both for management and prevention of the disease in individual patients and for the broader public health efforts to overcome all childhood illnesses. For the new World Health Organization (WHO)-supported, public-/private-sector collaboration (Global Alliance) to eliminate LF through once-yearly drug treatment, this recognition means that children will be not only the principal beneficiaries of LF elimination but also a population particularly important to target in order for the programme to achieve its twin goals of interrupting transmission and preventing disease.

Global malnutrition

The four most important forms of malnutrition worldwide (protein-energy malnutrition, iron deficiency and anaemias (IDA), vitamin A deficiency (VAD), and iodine deficiency disorders (IDD)) are examined below in terms of their global and regional prevalences, the age and gender groups most affected, their clinical and public health consequences, and, especially, the recent progress in country and regional quantitation and control. Zinc deficiency, with its accompanying diminished host resistance and increased susceptibility to infections, is also reviewed. WHO estimates that malnutrition (underweight) was associated with over half of all child deaths in developing countries in 1995. The prevalence of stunting in developing countries is expected to decline from 36% in 1995 to 32.5% in 2000; the numbers of children affected (excluding China) are expected to decrease from 196.59 millions to 181.92 millions. Stunting affects 48% of children in South Central Asia, 48% in Eastern Africa, 38% in South Eastern Asia, and 13-24% in Latin America. IDA affects about 43% of women and 34% of men in developing countries and usually is most serious in pregnant women and children, though non-pregnant women, the elderly, and men in hookworm-endemic areas also comprise groups at risk. Clinical VAD affects at least 2.80 million preschool children in over 60 countries, and subclinical VAD is considered a problem for at least 251 millions; school-age children and pregnant women are also affected. Globally about 740 million people are affected by goitre, and over two billions are considered at risk of IDD. However, mandatory salt iodisation in the last decade in many regions has decreased dramatically the percentage of the population at risk. Two recent major advances in understanding the global importance of malnutrition are (1) the data of 53 countries that links protein-energy malnutrition (assessed by underweight) directly to increased child mortality rates, and (2) the outcome in 6 of 8 large vitamin A supplementation trials showing decreases of 20-50% in child mortality.

An analysis of the safety of the single dose, two drug regimens used in programmes to eliminate lymphatic filariasis

This review of the safety of the co-administration regimens to be used in programmes to eliminate lymphatic filariasis (albendazole + ivermectin or albendazole + diethylcarbamazine [DEC]) is based on 17 studies conducted in Sri Lanka, India, Haiti, Ghana, Tanzania, Kenya, Ecuador, the Philippines, Gabon, Papua New Guinea, and Bangladesh. The total data set comprises 90,635 subject exposures and includes individuals of all ages and both genders. Results are presented for hospital-based studies, laboratory studies, active surveillance of microfilaria-positive and microfilaria-negative individuals, and passive monitoring in both community-based studies and mass treatment programmes of individuals treated with albendazole (n = 1538), ivermectin (9822), DEC (576), albendazole + ivermectin (7470), albendazole + DEC (69,020), or placebo (1144). The most rigorous monitoring, which includes haematological and biochemical laboratory parameters pre- and post-treatment, provides no evidence that consistent changes are induced by any treatment; the majority of abnormalities appear to be sporadic, and the addition of albendazole to either ivermectin or DEC does not increase the frequency of abnormalities. Both DEC and ivermectin show, as expected, an adverse event profile compatible with the destruction of microfilariae. The addition of albendazole to either single-drug treatment regimen does not appear to increase the frequency or intensity of events seen with these microfilaricidal drugs when used alone. Direct observations indicated that the level of adverse events, both frequency and intensity, was correlated with the level of microfilaraemia. In non microfilaraemic individuals, who form 80-90% of the 'at risk' populations to be treated in most national public health programmes to eliminate lymphatic filariasis (LF), the event profile with the compounds alone or in combination does not differ significantly from that of placebo. Data on the use of ivermectin + albendazole in areas either of double infection (onchocerciasis and LF), or of loiais (with or without concurrent LF) are still inadequate and further studies are needed. Additional data are also recommended for populations infected with Brugia malayi, since most data thus far derive from populations infected with Wuchereria bancrofti.

Malnutrition and parasitic helminth infections

The Global Burden of Disease caused by the 3 major intestinal nematodes is an estimated 22.1 million disability-adjusted life-years (DALYs) lost for hookworm, 10.5 million for Ascaris lumbricoides, 6.4 million for Trichuris trichiura, and 39.0 million for the three infections combined (as compared with malaria at 35.7 million) (World Bank, 1993; Chan et al. 1994); these figures illustrate why some scarce health care resources must be used for their control. Strongyloides stercoralis is the fourth most important intestinal worm infection; its nutritional implications are discussed, and the fact that its geographic distribution needs further study is emphasized. Mechanisms underlying the malnutrition induced by intestinal helminths are described. Anorexia, which can decrease intake of all nutrients in tropical populations on marginal diets, is likely to be the most important in terms of magnitude and the probable major mechanism by which intestinal nematodes inhibit growth and development. We present a revised and expanded conceptual framework for how parasites cause/aggravate malnutrition and retard development in endemic areas. Specific negative effects that a wide variety of parasites may have on gastrointestinal physiology are presented. The synergism between Trichuris and Campylobacter, intestinal inflammation and growth failure, and new studies showing that hookworm inhibits growth and promotes anaemia in preschool (as well as school-age) children are presented. We conclude by presenting rationales and evidence to justify ensuring the widest possible coverage for preschool-age children and girls and women of childbearing age in intestinal parasite control programmes, in order to prevent morbidity and mortality in general and specifically to help decrease the vicious intergenerational cycle of growth failure (of low-birth-weight/intrauterine growth retardation and stunting) that entraps infants, children and girls and women of reproductive age in developing areas.

Ivermectin: effectiveness in lymphatic filariasis

This detailed review of the published studies underlying ivermectin's recent registration for use in lymphatic filariasis (LF) demonstrates the drug's single-dose efficacy (over the range of 20-400 microg/kg) in clearing microfilaraemia associated with both Wuchereria bancrofti and Brugia malayi infections of humans. While doses as low as 20 microg/kg could effect transient microfilarial (mf) clearance, higher dosages induced greater and more sustained mf reduction. The single dose of 400 microg/kg yielded maximal responses, but a number of practical considerations suggest that either 400 microg/kg or 200 microg/kg doses would be acceptable for use in LF control programmes. Associated safety assessments indicate that adverse events, which occur commonly following treatment of microfilaraemic individuals, develop not because of drug toxicity but because of host inflammatory responses to dying microfilariae killed by the ivermectin treatment. Ivermectin is, therefore, a highly effective and generally well tolerated microfilaricide that may soon become an essential component of many public health initiatives to interrupt transmission of lymphatic filarial infection in an effort to eliminate LF globally.

Evolution of immunologic responsiveness of persons living in an area of endemic bancroftian filariasis: a 17-year follow-up

On an island in which bancroftian filariasis is endemic, 29 microfilaremic and 16 "endemic normal" (EN) subjects initially studied in 1974-1975 were reevaluated 17 years later. Eleven persons remained microfilaremic, whereas 18 had cleared both microfilaremia and antigenemia. Despite decreased infection on the island, antibody levels remained relatively constant for the subjects with persistent microfilaremia (Mf(+/+)), in contrast to sharp decreases for both EN subjects and subjects with cleared microfilaremia (Mf(+/-)). Although clinically indistinguishable from the EN subjects, the Mf(+/-) group had antibody levels (IgG, IgG4, and IgE) significantly lower than those of the EN subjects. Lymphocyte responses to parasite antigens were marginally greater in Mf(+/-) than in Mf(+/+) subjects, but both groups remained less cell responsive (as measured by proliferation, interleukin-5, interleukin-10, interferon-gamma, and granulocyte-macrophage colony-stimulating factor) than did the EN subjects. These findings suggest that, for microfilaremic persons, complete clearance of infection is not sufficient to restore "normal" immune responsiveness; filarial infection may induce very long-term deficits in the ability to respond to parasite antigens.

The global programme to eliminate lymphatic filariasis

Ten years ago, no one foresaw that in the year 2000 there would be a Global Programme to Eliminate Lymphatic Filariasis (GPELF) that is already 2 years old, active in 18 of the 80 endemic countries, and operating under a wholly new paradigm in public health - a paradigm affirming that public/private sector partnerships are essential in sharing both responsibilities and responses to global health problems. What has driven the LF Elimination Programme to this point? Where it is now headed? What will be required to sustain its momentum? What will its impact be? These are the issues addressed below.

The role of albendazole in programmes to eliminate lymphatic filariasis

Citing earlier advances in the treatment of lymphatic filariasis [particularly the effectiveness of single-dose diethylcarbamazine (DEC) in reducing microfilaraemia and its enhanced effectiveness when co-administered with single-dose ivermectin], Eric Ottesen, Mahroof Ismail and John Horton consider recent studies on the antifilarial activity of albendazole that have led to the current recommendations for its use in single-dose regimens in conjunction with either DEC or ivermectin for large-scale control/elimination programmes. Furthermore, the potential of albendazole as a macrofilaricide for treating individual patients with lymphatic filarial infections is emphasized as one of a number of important research questions that remain to be explored.

Eosinophil sequestration and activation are associated with the onset and severity of systemic adverse reactions following the treatment of onchocerciasis with ivermectin

To investigate the role of eosinophil activation and sequestration in the development and severity of adverse reactions after the treatment of Onchocerca volvulus infection, 40 O. volvulus-infected Ghanaians were randomized to receive placebo or standard- or high-dose ivermectin. Subjects were examined for typical physiologic and clinical events before and up to 48 h after treatment. Plasma samples were tested for interleukin (IL)-5 and eosinophil degranulation products (e.g., eosinophil-derived neurotoxin, EDN). After treatment, peripheral eosinophil counts declined in ivermectin-treated groups (P<.001), whereas circulating levels of IL-5 (P<.01) and EDN (P<.05) increased. Cumulative levels of IL-5 and EDN correlated with reaction scores (P<.01). High-dose ivermectin was associated with more-severe reactions, more-profound eosinopenia, and higher circulating levels of IL-5 and EDN, compared with the standard dose. These results suggest that eosinophil sequestration and activation/degranulation are associated with the initiation and severity of ivermectin-associated adverse reactions.

Filariasis and erisipela in Santo Domingo

This study examined acute-convalescent changes in diagnostic anti-streptococcal antibodies by the anti-streptolysin O (ASO) and anti-DNAase B (ADAB) tests among patients (n 28) with lymphedema and recurrent erisipela of the lower limb, comparing them with endemic normal control residents (n=25). The study was based in Villa Francisca, an urban focus of Bancroftian filariasis in eastern Santo Domingo, capital of the Dominican Republic. The acute signs and symptoms of erisipela were consistent with a diagnosis of bacterial cellulitis. The ASO test was especially successful at demonstrating a rise in mean titer during convalescence, whereas the ADAB produced about the same frequency of significant increases (0.2 log titer) as did the ASO. When subjects were scored as responders if mounting a minimal titer increase by either test, patients were found more frequently positive than were controls (chi2=5.3, P=0.02). About half (54%) of all patients mounted at least a minimal antibody increase. Filaria-specific IgG4 antibodies were absent from all sera of 20 residents of a nonendemic Dominican mountain town but appeared in about two-thirds of the sampled residents of the endemic barrio. Notably however, levels did not change between the acute phase and convalescence. These findings are consistent with the hypothesis that recurrent streptococcal invasion of the lymphatics may be a significant factor triggering or amplifying lymphedema and elephantiasis in patients with chronic filariasis.

Strategies and tools for the control/elimination of lymphatic filariasis

Lymphatic filariasis infects 120 million people in 73 countries worldwide and continues to be a worsening problem, especially in Africa and the Indian subcontinent. Elephantiasis, lymphoedema, and genital pathology afflict 44 million men, women and children; another 76 million have parasites in their blood and hidden internal damage to their lymphatic and renal systems. In the past, tools and strategies for the control of the condition were inadequate, but over the last 10 years dramatic research advances have led to new understanding about the severity and impact of the disease, new diagnostic and monitoring tools, and, most importantly, new treatment tools and control strategies. The new strategy aims both at transmission control through community-wide (mass) treatment programmes and at disease control through individual patient management. Annual single-dose co-administration of two drugs (ivermectin + diethylcarbamazine (DEC) or albendazole) reduces blood microfilariae by 99% for a full year; even a single dose of one drug (ivermectin or DEC) administered annually can result in 90% reductions; field studies confirm that such reduction of microfilarial loads and prevalence can interrupt transmission. New approaches to disease control, based on preventing bacterial superinfection, can now halt or even reverse the lymphoedema and elephantiasis sequelae of filarial infection. Recognizing these remarkable technical advances, the successes of recent control programmes, and the biological factors favouring elimination of this infection, the Fiftieth World Health Assembly recently called on WHO and its Member States to establish as a priority the global elimination of lymphatic filariasis as a public health problem.

Evidence for protective immunity to bancroftian filariasis in the Cook Islands

To challenge the concept of protective immunity in lymphatic filariasis, 19 adult residents of a Wuchereria bancrofti-endemic island who had been diagnosed 17 years earlier as putatively immune endemic normals (PI/EN) were reexamined. Even with continued exposure to infection, all 19 had maintained their apparent infection-free status. Studies to define the mechanisms underlying this putative immunity revealed that cellular immune responses (including proliferation; generation of interleukin [IL]-2, IL-5, IL-10, interferon-gamma, and granulocyte-macrophage colony-stimulating factor) to adult- and microfilarial-stage antigens, but not antibody responses, were markedly greater than those of 20 age-matched, infected patients. Furthermore, the PI/EN group was comprised of high- and low-responding persons who were clinically indistinguishable. These findings provide evidence that protective immunity to lymphatic filariasis does occur and that it is probably T cell-mediated.

Identification of surface molecules associated with physiologic activation of eosinophils. Application of whole-blood flow cytometry to eosinophils

Activation is central to the eosinophil's functional role as an immune responder cell. To evaluate such activation in cells freshly isolated from peripheral blood, a method for whole-blood immunostaining and flow cytometry-based eosinophil selection was developed. Simultaneous comparison of purified eosinophils and whole-blood cells revealed significant differences in the levels of expression of various surface molecules, which suggested that the purification process activated the eosinophils. Subsequent analyses were conducted with the whole-blood assay. When eosinophils from helminth-infected persons (n = 18) were compared with those from normal individuals (n = 10), the early activation marker CD69 was found to be significantly increased (geometric mean (GM) = 4.3 vs. 1.0%, p = 0.04). The granulocyte activation marker CD66 was also up-regulated on eosinphils from helminth patients (GM = 53.3 vs. 31.0%, p = 0.044), as was the tetraspan family molecule CD81 (TAPA-1; GM = 79.4 vs. 48.2%, p = 0.02). Conversely, in vivo CD23 (FcepsilonRII) expression on eosinophils was decreased in the presence of parasitic infection (GM = 0.9 vs. 5.7%, p = 0.02). Expression of the eosinophil surface molecules CD69, CD81, and CD23 was significantly enhanced after cytokine stimulation in vitro with IL-3 or GM-CSF. In vivo, specific anthelmintic therapy resulted in decreased CD66 and CD25 expression (p < 0.05 compared with pretreatment) to levels approaching those seen in uninfected normal individuals. These findings indicate the dynamic nature of eosinophil surface molecules and demonstrate an important role for whole-blood staining in developing an understanding of the nature of eosinophil activation and of their role in inflammatory reactions to helminth parasites.

Identification of surface molecules associated with physiologic activation of eosinophils. Application of whole-blood flow cytometry to eosinophils

Activation is central to the eosinophil's functional role as an immune responder cell. To evaluate such activation in cells freshly isolated from peripheral blood, a method for whole-blood immunostaining and flow cytometry-based eosinophil selection was developed. Simultaneous comparison of purified eosinophils and whole-blood cells revealed significant differences in the levels of expression of various surface molecules, which suggested that the purification process activated the eosinophils. Subsequent analyses were conducted with the whole-blood assay. When eosinophils from helminth-infected persons (n = 18) were compared with those from normal individuals (n = 10), the early activation marker CD69 was found to be significantly increased (geometric mean (GM) = 4.3 vs. 1.0%, p = 0.04). The granulocyte activation marker CD66 was also up-regulated on eosinphils from helminth patients (GM = 53.3 vs. 31.0%, p = 0.044), as was the tetraspan family molecule CD81 (TAPA-1; GM = 79.4 vs. 48.2%, p = 0.02). Conversely, in vivo CD23 (FcepsilonRII) expression on eosinophils was decreased in the presence of parasitic infection (GM = 0.9 vs. 5.7%, p = 0.02). Expression of the eosinophil surface molecules CD69, CD81, and CD23 was significantly enhanced after cytokine stimulation in vitro with IL-3 or GM-CSF. In vivo, specific anthelmintic therapy resulted in decreased CD66 and CD25 expression (p &lt; 0.05 compared with pretreatment) to levels approaching those seen in uninfected normal individuals. These findings indicate the dynamic nature of eosinophil surface molecules and demonstrate an important role for whole-blood staining in developing an understanding of the nature of eosinophil activation and of their role in inflammatory reactions to helminth parasites.

Evaluation of a polymerase chain reaction-based assay for diagnosis of Wuchereria bancrofti infection

To assess the utility of a polymerase chain reaction (PCR)-based method for diagnosis of Wuchereria bancrofti infection, blood, plasma, and paraffin-embedded tissue samples were tested using a PCR-based assay that detects a W. bancrofti-specific repetitive DNA sequence. The assay was positive in 100 microL of blood from 40 of 42 microfilaria-positive subjects, the 2 subjects with negative assays having microfilarial counts of 1. Samples from 127 uninfected subjects were PCR-negative. The assay was also positive in 7 of 10 daytime samples in regions where infection is nocturnally periodic; PCR amplification from paraffin-embedded sections established the diagnosis of W. bancrofti infection in another 2 cases. A microtiter ELISA plate-based method was developed for rapid evaluation of large numbers of samples. These results suggest that this PCR-based assay will be useful in diagnosis of W. bancrofti infection in a variety of clinical settings.

Elevations in granulocyte-macrophage colony-stimulating factor and interleukin-5 levels precede posttreatment eosinophilia in onchocerciasis

The eosinophil survival assay was used to quantitate cytokines in 17 serial serum samples from 10 patients treated for onchocerciasis with diethylcarbamazine. Eosinophils isolated from normal donors were cultured for 4 days in the presence of patients' sera, and cell viability was determined. Serum specimens from 9 of 10 patients enhanced eosinophil survival from 4.8% +/- 2.2% (mean +/- SE) before treatment to 50.0% +/- 6.4% after treatment. Survival enhancement activity peaked before posttreatment eosinophilia. Antibodies to interleukin (IL)-5, granulocyte-macrophage colony-stimulating factor (GM-CSF), and IL-3 were used to block cytokine activity in 22 serum samples. Antibodies to IL-5 blocked survival in 5 samples, antibodies to GM-CSF blocked survival in 6 samples, and a combination of antibodies to IL-5 and GM-CSF blocked survival in 8 additional samples. Overall, posttreatment sera from patients treated for onchocerciasis enhanced eosinophil survival; both GM-CSF and IL-5 may promote the posttreatment eosinophilia in filarial infection.

A polymerase chain reaction assay for detection of the parasite Wuchereria bancrofti in human blood samples

To identify Wuchereria bancrofti DNA sequences that could be used as the basis for a simple and rapid parasite detection assay, a genomic library of W. bancrofti was constructed and screened for highly repeated DNA. The repeat found with the highest copy number was 195 basepairs (bps) long, 77% AT, and 300 copies per haploid genome. This sequence was designated the Ssp I repeat because it has a unique recognition site for that restriction endonuclease in all or most of the repeat copies. The Ssp I repeat DNA family is dispersed, genus-specific, and exists in all of the different geographic isolates of W. bancrofti tested. Based on DNA sequence analysis of this repeat, we have developed an assay to detect very small quantities of W. bancrofti DNA using the polymerase chain reaction (PCR). With this PCR assay, the Ssp I repeat was detected in as little as 1 pg of w. bancrofti genomic DNA (about 1% of the DNA in one microfilaria) added to 100 microliters of human blood. The PCR assay also amplified Ssp I repeat DNA from geographic isolates of W. bancrofti from around the world but not from other species of filariae or from human or mosquito DNA. Microfilaria-positive human blood samples collected in Mauke, Cook Islands were shown to be Ssp I PCR-positive, while microfilaria-negative samples were PCR-negative. The specificity and sensitivity of the Ssp I PCR assay indicates that this approach has significant potential for improved screening of large human populations for active W. bancrofti infection.

High levels of spontaneous and parasite antigen-driven interleukin-10 production are associated with antigen-specific hyporesponsiveness in human lymphatic filariasis

To determine whether counterregulation by interleukin (IL)-10 plays a role in the generation or maintenance of the antigen-specific hyporesponsiveness seen in asymptomatic microfilaremic (MF) patients, parasite antigen (PAg)- and nonparasite antigen (NPAg)-driven IL-10 production by peripheral blood mononuclear cells (PBMC) was studied in 10 MF patients and in ll patients with chronic lymphatic pathology (CP). PBMC from MF patients spontaneously secreted 10-fold more IL-10 than did PBMC from patients with CP. PAg also induced significantly more IL-10 production by PBMC from CP patients. There was a negative correlation between PAg driven IL-10 production by PBMC and PAg-specific T cell proliferation in the MF group. IL-10 secretion by plastic adherent cells from MF persons was higher in response to PAg than NPAg, whereas IL-6 and tumor necrosis factor-alpha secretion were equivalent for PAg and NPAg, suggesting that PAg preferentially induces IL-10 secretion in these cells. Thus, PAg-induced IL-10 likely plays an important role in down-regulating antigen-specific proliferative responses in MF patients.

Syndrome resembling tropical pulmonary eosinophilia but of non-filarial aetiology: serological findings with filarial antigens

Although the tropical pulmonary eosinophilia (TPE) syndrome of filarial aetiology has very distinctive clinical and immunological features, its clinical profile is not unique; other helminths sometimes induce similar presentations. We carefully evaluated 7 individuals with non-filarial TPE-like syndromes and found that serological tests based on detection of 'antifilarial' immunoglobulin (Ig) G, IgG4, and IgE antibodies that are usually considered diagnostic for filarial TPE were equally elevated in patients with non-filarial, TPE-like syndromes and were therefore unhelpful diagnostically. The apparent reasons were immunological hyper-responsiveness of such individuals and the shared (i.e., cross-reactive) antigenicity found in the filarial antigen preparations used routinely for diagnosis. Because appropriate treatment for those different pulmonary eosinophilia conditions requires different drugs and management, and because delay in effective treatment results in significant morbidity in such patients, diagnostic capabilities must be improved by identifying and obtaining unique antigens that can serologically discriminate between filarial TPE and other similar, but non-filarial, pulmonary eosinophilia syndromes.

Clearance of circulating filarial antigen as a measure of the macrofilaricidal activity of diethylcarbamazine in Wuchereria bancrofti infection

Small doses of diethylcarbamazine (DEC) clear microfilariae (MF) from the blood of Wuchereria bancrofti-infected persons, but the dose and regimen required to kill adult worms is not clearly defined. A prospective study was undertaken to examine the macrofilaricidal effect of DEC and the ability of an assay for circulating filarial antigen (CFA) to define the effect. Twenty-five MF-positive subjects and 7 MF-negative but CFA-positive subjects were treated with DEC and followed for 18 months. Of the 25 MF-positive patients, 24 cleared MF, and 22 of 26 CFA-positive subjects cleared CFA. A significantly greater decrease in antifilarial IgG4 was seen in patients who cleared CFA than in those who did not. The complete clearance of CFA observed after therapy with DEC indicates that assessment of CFA clearance is a useful means for detecting macrofilaricidal effects of antifilarial chemotherapy.

Onchocerca volvulus: parasitologic and serologic responses in experimentally infected chimpanzees and mangabey monkeys

Six chimpanzees (Pan troglodytes) and six mangabey monkeys (Cercocebus atys) were inoculated with Onchocerca volvulus third-stage larvae (L3) of West African origin. Two chimpanzees each received 200, 300, or 400 L3, while three mangabeys each received either 50 or 250 L3. All six chimpanzees became microfilaria positive between 11 and 25 months postinoculation (PI), while two of the six mangabeys were skin-snip positive at 24 and 37 months PI, respectively. All chimpanzees developed antibodies to two native antigens of 14 and 22 kDa and to the recombinant antigens OV16, OC3.6, and OC9.3. Marked antibody responses were observed in the mangabey monkeys, and in general, the responses were similar to those observed in the chimpanzees. However, in the mangabeys, these responses did not generally manifest themselves until later in the infection. The results of this study suggest that in chimpanzees, the smallest inoculum used, 200 L3, was sufficient to initiate consistent infections that had parasitologic and immunologic parameters equivalent to animals inoculated with larger numbers of larvae. Similarly, inoculation of mangabey monkeys with small numbers of larvae appeared to be as likely to establish infection and induce immunologic responses as did inoculation of larger numbers of larvae. Microfilaria-positive chimpanzees and mangabey monkeys were examined by three conventional imaging techniques (X ray, ultrasound, and magnetic resonance imaging (MRI)), but no adult worms or nodules could be identified in any animal.(ABSTRACT TRUNCATED AT 250 WORDS)

Immune responsiveness and the pathogenesis of human onchocerciasis

Prominent antibody but minimal cellular proliferative responses to parasite antigen typify the systemic immune response of patients with onchocerciasis. While components of this response are proinflammatory (and antiparasitic), the primary force driving the immune system is the need to contain or limit inflammation around microfilariae that die in the skin or elsewhere at rates up to hundreds of thousands per day. These dying parasites initiate local inflammatory reactions, with the result being "bystander" tissue damage, which cumulatively determines host pathology. Local and systemic immune mechanisms to contain inflammation (e.g., blocking antibodies, down-regulating cytokines) are prominent in infected patients, and their delineation is crucial to understanding the pathogenesis of onchocercal disease in the skin, eye, and elsewhere. The degree of pathology appears directly related to both microfilarial numbers and the intensity of proinflammatory responses to them and inversely related to the effectiveness of specific mechanisms to suppress this inflammation.

Onchocerciasis in endemic and nonendemic populations: differences in clinical presentation and immunologic findings

To characterize the clinical and laboratory features of onchocerciasis in visitors to endemic areas and to compare them with those seen in endemic subjects, 20 returned visitors and 21 endemic subjects with onchocerciasis were evaluated. Dermatitis was the most frequent clinical finding among the returned visitors. None had nodules or eye disease and, in contrast to the endemic subjects, microfiladermia was often absent or of low density. All persons studied had antibody responses measurable by ELISA to both soluble Onchocerca volvulus antigen and a panel of diagnostic recombinant antigens. Eosinophil and IgE levels were significantly higher in the endemic group, as was the capacity of peripheral blood mononuclear cells from this group to produce the T helper cell-like cytokines interleukin-4 and -5. It is likely that the chronicity and intensity of infection in endemic subjects account for the clinical and immunologic differences observed between the 2 groups.

Ivermectin in human medicine

Ivermectin is a potent macro-cyclic lactone causing paralysis in many nematodes and arthropods through an influx of chloride ions across cell membranes. It is currently the drug of choice for human onchocerciasis and shows potent microfilaricidal activity against the other major filarial parasites of human (Wuchereria bancrofti, Brugia malayi, Loa loa and Mansonella ozzardi) but not against M. perstans. Whether or not it also kills the adult-stage of these parasites is currently under study. Ivermectin also has excellent efficacy in both human strongyloidiasis and cutaneous larva migrans for which good alternative treatments have not been available; and it is as effective as currently available drugs against the intestinal nematodes Ascaris lumbricoides, Trichuris trichiura and Enterobius vermicularis; against the human hookworms it shows only partial efficacy. Preliminary studies indicate that ivermectin has the potential to become the drug of choice for ectoparasitic infestations (mites, lice) of humans as well.

Cloning and characterization of a potentially protective chitinase-like recombinant antigen from Wuchereria bancrofti

While there is no direct evidence demonstrating the existence of protective immunity to Wuchereria bancrofti infection in humans, the presence of individuals, in populations in areas where infection is endemic, with no clinical evidence of past or current infection despite appreciable exposure to the infective larvae, suggests that protective immunity to filarial parasites may occur naturally. Earlier work indicated that such putatively immune individuals generated antibodies to a 43-kDa antigen from larval extracts of the related filarial parasite Brugia malayi that was recognized by only 8% of the infected population. With rabbit antiserum raised against this 43-kDa antigen, this current study identified a recombinant clone, WbN43, with an insert size of 2.3 kb, from a W. bancrofti genomic expression library. The recombinant fusion protein was differentially recognized by the putatively immune individuals but not by the infected patients. The coding sequence (684 bp) from the 5' end had significant sequence similarity to chitinases from Serratia marcescens, Bacillus circulans, Streptomyces plicatus, and B. malayi. Peptide sequencing of the expressed product also defined a chitinase-like sequence. Molecular characterization indicated WbN43 to be a low-copy-number gene, with expression predominantly in infective larvae and microfilariae but not in adult parasites.

Interleukin-6 and tumor necrosis factor in the pathogenesis of adverse reactions after treatment of lymphatic filariasis and onchocerciasis

Adverse reactions following treatment of onchocerciasis and bancroftian filariasis are common and frequently severe. They are generally caused not by direct drug toxicity but by host inflammatory responses to dying microfilariae. To define the responsible mechanism, serial blood levels of interleukin-6 (IL-6) and tumor necrosis factor (TNF) were studied in 15 microfilaria-positive patients (10 with bancroftian filariasis, 5 with onchocerciasis) and 4 microfilaria-negative persons after diethylcarbamazine treatment. Elevations in IL-6 correlated with the occurrence and severity of clinical symptoms after treatment; for the onchocerciasis patients IL-6 levels directly reflected pretreatment intensity of infection. Serum TNF levels also rose but did not correlate directly with infection intensity or reaction severity. Microfilaria-negative controls remained asymptomatic with no significant rise in either cytokine. These findings suggest an etiologic role for systemically elevated cytokines in the inflammatory reactions developing after treatment of filarial infections in humans.

Long-term effect of prenatal exposure to maternal microfilaraemia on immune responsiveness to filarial parasite antigens

To identify long-term effects of prenatal exposure to maternal filarial-parasite infection, we assessed lymphocyte responses in 21 Polynesian children born 17-19 years previously to mothers diagnosed as being microfilaraemic or infection-free. All children lived on an island endemic for bancroftian filariasis but were free from infection at the time of study. While children (n = 10) of infection-free mothers responded vigorously to microfilarial antigen with lymphocyte proliferation, production of interleukin 2 (IL-2), IL-5, IL-10, granulocyte macrophage colony-stimulating factor (GM-CSF), and interferon gamma (IFN-gamma), cellular hyporesponsiveness was seen in children (n = 11) born to microfilaraemic mothers. The hyporesponsiveness appeared restricted to microfilarial antigens and did not extend to non-parasite antigens. These findings suggest that hyporesponsiveness resulted from in-utero acquisition of tolerance to microfilarial antigens in chronically-infected mothers.

Effectiveness of diethylcarbamazine in treating loiasis acquired by expatriate visitors to endemic regions: long-term follow-up

Although successful treatment of loiasis with diethylcarbamazine (DEC) has been reported, little is known about the long-term success rate of therapy or the predisposing factors for treatment failure. To address these questions, 32 patients were followed 2-15 years (median, 4.5) after DEC treatment; all had acquired infection while expatriate visitors to endemic areas of Africa. Using a strict definition of successful treatment, 12 (38%) appeared to be cured after one course of therapy and 5(16%) after two courses. Of the remaining 15 patients, 3 continued to be symptomatic despite more than four courses of treatment. Although 12 of the 17 patients who relapsed did so within 1 year of treatment, several had relatively long asymptomatic periods (2-8 years). There was no predictive difference in clinical or laboratory parameters (including eosinophilia and specific filarial serology) between patients requiring one or more courses of therapy.

Ivermectin plus diethylcarbamazine: an additive effect on early microfilarial clearance

The effects of ivermectin, diethylcarbamazine (DEC), and the combination of both drugs on levels of microfilaremia (mf) were studied in 30 male Polynesian Wuchereria bancrofti carriers. Microfilarial densities were measured 30 min (H1/2), 1 hr (H1), and 2, 4, 8, 24, and 96 hr (H2, H4, H8, H24, and H96) after supervised single doses of ivermectin plus DEC (400 micrograms/kg plus 1 mg/kg, respectively, 400 micrograms/kg plus 3 mg/kg, respectively, and 400 micrograms/kg plus 6 mg/kg, respectively), DEC (6 mg/kg) alone, and ivermectin (400 micrograms/kg and 100 micrograms/kg, respectively) alone given to six groups of five patients each. The results showed that 1) DEC alone or combined with ivermectin induced a rapid clearance of mf after drug intake; at H1/2, the number of circulating microfilariae was reduced to 16%, 8%, 28%, and 31%, respectively, of pretreatment values in the groups receiving ivermectin plus DEC (400 micrograms/kg plus 1 mg/kg, 400 micrograms/kg plus 3 mg/kg, and 400 micrograms/kg plus 6 mg/kg) and DEC (6 mg/kg) alone; 2) ivermectin alone induced a rapid increase of mf densities during the first 2 hr, followed by a sharp decrease from H4 to H96; and 3) between H8 and H96, mf clearance was almost complete with the combination of ivermectin and DEC. A comparison among groups did not show any synergistic interaction between ivermectin and DEC on the clearance of microfilaria, with the effect of each drug being additive to each another.

Cytokine control of parasite-specific anergy in human lymphatic filariasis. Preferential induction of a regulatory T helper type 2 lymphocyte subset

The immunological mechanisms involved in maintenance of an asymptomatic microfilaremic state (MF) in patients with lymphatic filariasis remain undefined. MF patients have impaired filarial antigen (Ag)-specific lymphocyte proliferation and decreased frequencies (Fo) of Ag-specific T cells, and yet elevated serum IgE and antifilarial IgG4. To investigate the mechanism of Ag-specific anergy in MF patients in contrast to amicrofilaremic individuals with chronic lymphatic obstruction (CP), the Fo of Ag-specific lymphocytes from peripheral blood mononuclear cells secreting either IL-4 or IFN-gamma were assessed by filter spot enzyme-linked immunosorbent assay, and IL-10 and transforming growth factor-beta (TGF-beta) mRNA transcript levels were assessed by a semiquantitative reverse transcriptase polymerase chain reaction technique. The Fo of filaria-specific IL-4-secreting lymphocytes were equivalent in both MF (geometric mean [GM] = 1:11,700) and CP (GM = 1:29,300 P = 0.08), whereas the Fo of IFN-gamma-secreting lymphocytes were lower in MF (GM = 1:39,300) than in CP (GM = 1:4,200, P < 0.01). When the ratio of IL-4/IFN-gamma (T helper type 2 [Th2]/Th1)-secreting cells was examined, MF subjects showed a predominant Th2 response (8:1) compared with a Th1 response in CP individuals (1:4). mRNA transcript levels of IL-10 were also significantly elevated in MF compared with CP individuals (P < 0.01). Further, IL-10 and TGF-beta were shown to have a role in modulating the Ag-specific anergy among MF subjects, in that neutralizing anti-IL-10 or anti-TGF-beta significantly enhanced lymphocyte proliferation response (by 220-1,300%) to filarial Ags in MF individuals. These findings demonstrate that MF subjects respond to parasite antigen by producing a set of suppressive cytokines that may facilitate persistence of the parasite within humans while producing little clinical disease.

IL-4- and IL-5-secreting lymphocyte populations are preferentially stimulated by parasite-derived antigens in human tissue invasive nematode infections

Helminth infections in humans and animals are associated with strong T helper 2 (Th2) responses. To determine whether parasite-derived Ag preferentially expand a Th2-like cell population, a filter immunoplaque assay was used to enumerate the frequencies (F0) of PBMC and CD4(+)-enriched PBMC from individuals with helminth infections secreting selected cytokines in response to parasite-derived (PAg) and nonparasite antigens (NPAg). In 20 individuals with lymphatic filariasis, frequency analysis of PBMC secreting IL-4 and IFN-gamma indicated that the F0 of PAg-specific IL-4-secreting cells (geometric mean F0 (GM): 1/12,100) was 57-fold higher than the corresponding F0 of NPAg-reactive cells (GM: 1/692,000; p &lt; 0.02). In marked contrast, the F0 of IFN-gamma-secreting cells responding to PAg (GM: 1/2,700) did not differ from those of cells specific for NAPg (GM: 1/3,400; p = 0.83). In another group of helminth-infected individuals, the F0 of highly enriched CD4+ cells secreting IL-4 and IL-5 in response to PAg (GMs: 1/2,600 and 1/5,600 CD4+ cells, respectively) were also found to be significantly higher than those specific for NPAg (GMs: 1/291,000 and 1/303,000 CD4+; p &lt; 0.05 and p &lt; 0.01, respectively), whereas the corresponding F0 of IFN-gamma- and granulocyte-macrophage-CSF-secreting cells were equivalent for PAg and NPag. Furthermore, the proportion of PAg-specific IL-4- and IL-5-secreting CD4+ cells relative to all cells secreting the given cytokine were approximately 29-fold higher than the proportion of NPAg-specific cells secreting these cytokines. Again, the corresponding proportions of Ag-specific IFN-gamma-and GM-CSF-secreting CD4+ cells were equivalent for PAg and NPAg. Thus, in this ex vivo system, a circulating population of IL-4- and IL-5-secreting (Th2-like) cells has been shown to exist in humans; PAg appears to expand these cells preferentially.

IL-4- and IL-5-secreting lymphocyte populations are preferentially stimulated by parasite-derived antigens in human tissue invasive nematode infections

Helminth infections in humans and animals are associated with strong T helper 2 (Th2) responses. To determine whether parasite-derived Ag preferentially expand a Th2-like cell population, a filter immunoplaque assay was used to enumerate the frequencies (F0) of PBMC and CD4(+)-enriched PBMC from individuals with helminth infections secreting selected cytokines in response to parasite-derived (PAg) and nonparasite antigens (NPAg). In 20 individuals with lymphatic filariasis, frequency analysis of PBMC secreting IL-4 and IFN-gamma indicated that the F0 of PAg-specific IL-4-secreting cells (geometric mean F0 (GM): 1/12,100) was 57-fold higher than the corresponding F0 of NPAg-reactive cells (GM: 1/692,000; p < 0.02). In marked contrast, the F0 of IFN-gamma-secreting cells responding to PAg (GM: 1/2,700) did not differ from those of cells specific for NAPg (GM: 1/3,400; p = 0.83). In another group of helminth-infected individuals, the F0 of highly enriched CD4+ cells secreting IL-4 and IL-5 in response to PAg (GMs: 1/2,600 and 1/5,600 CD4+ cells, respectively) were also found to be significantly higher than those specific for NPAg (GMs: 1/291,000 and 1/303,000 CD4+; p < 0.05 and p < 0.01, respectively), whereas the corresponding F0 of IFN-gamma- and granulocyte-macrophage-CSF-secreting cells were equivalent for PAg and NPag. Furthermore, the proportion of PAg-specific IL-4- and IL-5-secreting CD4+ cells relative to all cells secreting the given cytokine were approximately 29-fold higher than the proportion of NPAg-specific cells secreting these cytokines. Again, the corresponding proportions of Ag-specific IFN-gamma-and GM-CSF-secreting CD4+ cells were equivalent for PAg and NPAg. Thus, in this ex vivo system, a circulating population of IL-4- and IL-5-secreting (Th2-like) cells has been shown to exist in humans; PAg appears to expand these cells preferentially.

Filarial infections

The seven filarial parasites of humans infect over 100 million people worldwide. These parasites are long lived, with adults living an average of 10 to 15 years and the microfilaria, probably 6 to 12 months. Importantly, as with most other helminth parasites, there is no replication of the adult parasite within the human host so that the extent of infection (that is, the number of adult worms one has) never increases after one leaves an endemic region and ceases to be exposed to the insect-borne infective larvae. This article will discuss the diagnosis and treatment of filarial infections, as well as some recent clinical advances.

Kinetics of serum and cellular interleukin-5 in posttreatment eosinophilia of patients with lymphatic filariasis

Peripheral blood eosinophil counts and serum levels and in vitro production of eosinophilopoietic cytokines were assessed before and at frequent intervals after diethylcarbamazine treatment of Bancroftian filariasis. Eosinophil counts peaked at day 7 after the start of treatment (359% +/- 118% of pretreatment levels) and declined to pretreatment levels by day 17. Serum interleukin (IL)-5, undetectable in 14 of 15 patients before treatment, rose sharply but transiently, with peak levels (32 +/- 7 pg/mL) 2 days after diethylcarbamazine treatment. Granulocyte-macrophage colony-stimulating factor and IL-3 were not detectable in serum at any time. In vitro mitogen-induced IL-5 levels decreased significantly in 7 of 9 patients 3 days after treatment when serum IL-5 was at near-peak levels. By day 10 IL-5 values increased in 8 of 9 patients compared with treatment values (P < .02). These data define the temporal relation between serum IL-5 levels and the subsequent development of eosinophilia and suggest that lymphocytes are the source of IL-5.

Characterization of a muscle-associated antigen from Wuchereria bancrofti

A recombinant clone, WbN1, isolated from a genomic expression library of Wuchereria bancrofti and showing restricted specificity at the DNA level (Southern and PCR analyses) for Wuchereria bancrofti and Brugia malayi has been previously described. Sequence analysis of WbN1 indicated that it had notable similarity to myosin. Further characterization using in situ hybridization has localized the mRNA in the muscle of the adult parasite and in the microfilariae. Rabbit polyclonal antiserum, raised against the recombinant WbN1 fused to the maltose-binding protein, recognized a 200-kDa polypeptide in immunoblots containing B. malayi antigen extracts. The same antibody also recognized myosin extracted from Brugia pahangi, Onchocerca volvulus, and Caenorhabditis elegans. Localization using the rabbit antiserum revealed the presence of the antigen in the adult muscle tissue and in the microfilariae; the same antibody inhibited the binding of a monoclonal antibody 28.2 (directed toward MHC B of C. elegans myosin) to the recombinant WbN1 antigen and also to purified C. elegans myosin. Based on homology data, structural location, competitive ELISA, and immunoblot we conclude that WbN1 is related to myosin or a similar myofibrillar protein.

Biochemical and immunologic characterization of a major IgE-inducing filarial antigen of Brugia malayi and implications for the pathogenesis of tropical pulmonary eosinophilia

A major allergen of the human filarial parasite Brugia malayi has been identified by two-dimensional immunoblot analysis using a serum pool from patients with tropical pulmonary eosinophilia. The allergen is composed of two Ag with M(r) 23 and M(r) 25 and acidic isoelectric point (Bm23-25). Immunoblots using affinity-purified IgE antibodies to BM23-25 indicated that Bm23-25 is expressed mainly in the microfilarial stage. Digestion of the allergen with endoglycosidases indicates that it has N-linked oligosaccharide chains. Analysis of the reactivity of T cells derived from patients with lymphatic filariasis revealed that the Bm23-25 allergen was capable of stimulating T cell proliferation; Bm23-25 was also shown to induce IgE production in vitro from PBMC derived from patients with either TPE or other filarial symptoms. Bronchoalveolar lavage fluid of patients with TPE contained IgE antibodies that recognized Bm23-25 strongly, an observation suggesting that the microfilarial allergen might be involved in the pathogenesis of the TPE syndrome.

Biochemical and immunologic characterization of a major IgE-inducing filarial antigen of Brugia malayi and implications for the pathogenesis of tropical pulmonary eosinophilia

A major allergen of the human filarial parasite Brugia malayi has been identified by two-dimensional immunoblot analysis using a serum pool from patients with tropical pulmonary eosinophilia. The allergen is composed of two Ag with M(r) 23 and M(r) 25 and acidic isoelectric point (Bm23-25). Immunoblots using affinity-purified IgE antibodies to BM23-25 indicated that Bm23-25 is expressed mainly in the microfilarial stage. Digestion of the allergen with endoglycosidases indicates that it has N-linked oligosaccharide chains. Analysis of the reactivity of T cells derived from patients with lymphatic filariasis revealed that the Bm23-25 allergen was capable of stimulating T cell proliferation; Bm23-25 was also shown to induce IgE production in vitro from PBMC derived from patients with either TPE or other filarial symptoms. Bronchoalveolar lavage fluid of patients with TPE contained IgE antibodies that recognized Bm23-25 strongly, an observation suggesting that the microfilarial allergen might be involved in the pathogenesis of the TPE syndrome.

Renal abnormalities in microfilaremic patients with Bancroftian filariasis

To determine the frequency of renal abnormalities occurring with Bancroftian filarial infections and to assess the effects of treatment on such abnormalities, we initiated a prospective, hospital-based study of 20 microfilaremic and five amicrofilaremic patients with Wuchereria bancrofti infections. Thorough clinical evaluations and detailed renal assessments were made prior to treatment and at multiple time points for 60 days following a standard twelve-day course of treatment with diethylcarbamazine (DEC). There were two important findings. First, even prior to DEC treatment, almost half of the microfilaremic patients had hematuria and/or proteinuria. Second, treatment with DEC induced these same abnormalities in almost all of the remaining microfilaremic patients. However, this DEC-induced hematuria and/or proteinuria was transient, and the long-term response to DEC in all of the microfilaremic patients was resolution of the abnormal renal findings during the two-month followup period. In the amicrofilaremic study patients, no hematuria or proteinuria was detected before, during, or after treatment with DEC.

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)

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.

Control of allergic reactivity in human filariasis. Predominant localization of blocking antibody to the IgG4 subclass

Patients with chronic helminth infections, despite having abundant basophils and mast cells specifically sensitized with antiparasite IgE and often exposed repeatedly to parasite Ag, rarely manifest allergic symptoms. This control of clinical allergic reactivity likely results from Ag-specific IgG "blocking antibodies" shown previously to be abundant in the sera of such patients. In the present study we used two approaches to determine in which of the four IgG subclasses this blocking activity was localized. First, specific antifilarial antibodies of each of the four IgG subclasses were quantified in the sera of 28 patients with Bancroftian filariasis and correlated with the levels of blocking activity in these sera (determined by histamine release assays). A significant correlation with blocking activity was seen only for antibodies of the IgG4 subclass, and, indeed, the correlation was especially strong in the group of totally asymptomatic patients (but with microfilariae circulating in the blood) in whom blocking antibody levels were highest. Interestingly, however, if the analysis excluded these asymptomatic microfilaremic patients and focused instead on those with lymphatic inflammatory pathology (who had relatively low levels of both serum blocking activity and specific IgG4 antibodies), then the small amount of blocking activity found in these sera correlated only with the levels of IgG1 subclass antibodies. The second approach utilized selective depletion of IgG4 (by anti-IgG4 affinity columns) from the sera of three microfilaremic patients with high levels of blocking activity and demonstrated clearly that removal of IgG4 abolished the majority of the blocking activity in these sera (53, 78, and 81%). These two sets of findings demonstrate a predominant role for specific IgG4 antibodies in blocking IgE-mediated allergic responses to the parasite Ag in vitro, but they also indicate that in some situations IgG1 antibodies can block such reactions. Furthermore, the correlation demonstrated between patients' clinical presentations and the levels of both their specific IgG4 antibodies and serum blocking activity suggests that these antibodies play a similar role in vivo as well.

Control of allergic reactivity in human filariasis. Predominant localization of blocking antibody to the IgG4 subclass

Patients with chronic helminth infections, despite having abundant basophils and mast cells specifically sensitized with antiparasite IgE and often exposed repeatedly to parasite Ag, rarely manifest allergic symptoms. This control of clinical allergic reactivity likely results from Ag-specific IgG "blocking antibodies" shown previously to be abundant in the sera of such patients. In the present study we used two approaches to determine in which of the four IgG subclasses this blocking activity was localized. First, specific antifilarial antibodies of each of the four IgG subclasses were quantified in the sera of 28 patients with Bancroftian filariasis and correlated with the levels of blocking activity in these sera (determined by histamine release assays). A significant correlation with blocking activity was seen only for antibodies of the IgG4 subclass, and, indeed, the correlation was especially strong in the group of totally asymptomatic patients (but with microfilariae circulating in the blood) in whom blocking antibody levels were highest. Interestingly, however, if the analysis excluded these asymptomatic microfilaremic patients and focused instead on those with lymphatic inflammatory pathology (who had relatively low levels of both serum blocking activity and specific IgG4 antibodies), then the small amount of blocking activity found in these sera correlated only with the levels of IgG1 subclass antibodies. The second approach utilized selective depletion of IgG4 (by anti-IgG4 affinity columns) from the sera of three microfilaremic patients with high levels of blocking activity and demonstrated clearly that removal of IgG4 abolished the majority of the blocking activity in these sera (53, 78, and 81%). These two sets of findings demonstrate a predominant role for specific IgG4 antibodies in blocking IgE-mediated allergic responses to the parasite Ag in vitro, but they also indicate that in some situations IgG1 antibodies can block such reactions. Furthermore, the correlation demonstrated between patients' clinical presentations and the levels of both their specific IgG4 antibodies and serum blocking activity suggests that these antibodies play a similar role in vivo as well.