Cellular immune responses of jirds to extracts of life cycle stages and adult excretory secretory products during the early development of Brugia pahangi

Pathological manifestations in lymphatic filariasis correlate with lack of inhibitory properties of IgG4 antibodies on IgE-activated granulocytes

Helminth parasites are known to be efficient modulators of their host's immune system. To guarantee their own survival, they induce alongside the classical Th2 a strong regulatory response with high levels of anti-inflammatory cytokines and elevated plasma levels of IgG4. This particular antibody was shown in different models to exhibit immunosuppressive properties. How IgG4 affects the etiopathology of lymphatic filariasis (LF) is however not well characterized. Here we investigate the impact of plasma and affinity-purified IgG/IgG4 fractions from endemic normals (EN) and LF infected pathology patients (CP), asymptomatic microfilaraemic (Mf+) and amicrofilaraemic (Mf-) individuals on IgE/IL3 activated granulocytes. The activation and degranulation states were investigated by monitoring the expression of CD63/HLADR and the release of granule contents (neutrophil elastase (NE), eosinophil cationic protein (ECP) and histamine) respectively by flow cytometry and ELISA. We could show that the activation of granulocytes was inhibited in the presence of plasma from EN and Mf+ individuals whereas those of Mf- and CP presented no effect. This inhibitory capacity was impaired upon depletion of IgG in Mf+ individuals but persisted in IgG-depleted plasma from EN, where it strongly correlated with the expression of IgA. In addition, IgA-depleted fractions failed to suppress granulocyte activation. Strikingly, affinity-purified IgG4 antibodies from EN, Mf+ and Mf- individuals bound granulocytes and inhibited activation and the release of ECP, NE and histamine. In contrast, IgG4 from CP could not bind granulocytes and presented no suppressive capacity. Reduction of both the affinity to, and the suppressive properties of anti-inflammatory IgG4 on granulocytes was reached only when FcγRI and II were blocked simultaneously. These data indicate that IgG4 antibodies from Mf+, Mf- and EN, in contrast to those of CP, natively exhibit FcγRI/II-dependent suppressive properties on granulocytes. Our findings suggest that quantitative and qualitative alterations in IgG4 molecules are associated with the different clinical phenotypes in LF endemic regions.

Effect of chemotherapeutic treatment on cytokine (IFN-gamma, IL-2, IL-4, IL-5, IL-10) gene transcription in response to specific antigens in Brugia malayi-infected Mastomys coucha

Cytokine (interferon (IFN)-gamma, interleukin (IL)-2, IL-4, IL-5, IL-10) gene transcription in response to filarial antigens was determined in peripheral blood mononuclear cells of Brugia malayi-infected Mastomys coucha in the course of untreated and chemotherapeutically abbreviated infections. Transcript levels in infected untreated animals suggest particular time courses for the various cytokines with ongoing parasite development and differing efficacies of female, male, microfilarial, and L3 antigens in inducing cytokine gene transcription. Gene transcription of both of Th1- and Th2-associated cytokines were initiated in the course of the infection in a manner that does not fit in a simple Th1-Th2 paradigm. IFN-gamma and IL-4 gene transcripts prevailed during prepatency. In case of the other cytokine genes considered in the study, transcription in general peaked around beginning of patency. During the phase of increasing microfilaremia (approximately 120-180 days p. i.) cytokine gene transcription was generally decreased. Later on, when the parasitemia had leveled off, except IFN-gamma, transcript levels often tended to increase. In chemotherapeutically treated animals, the outcome varied with the different efficacies of the drugs employed. The highly microfilaricidal cyclodepsipeptide BAY 44-4400 eliminated circulating microfilariae and partially sterilized adult worms without killing them. This kind of treatment hardly affected cytokine responses. In contrast, the therapy with Flubendazole, a selectively macrofilaricidal benzimidazole, and particularly the application of CGP 20376, a highly efficient microfilaricidal and macrofilaricidal benzthiazole, resulted in enhanced transcription of the Th1-associated IFN-gamma and IL-2 genes as well as of the Th2-associated IL-5 gene 2-3 months after treatment. IL-10 gene transcription seemed transiently increased after 1 month. There was no effect of any treatment on the IL-4 gene transcription.

Profiling the cellular immune response to multiple Brugia pahangi infections in a susceptible host

Human lymphatic filariasis is caused primarily by Brugia malayi and Wuchereria bancroffi. Unraveling this disease is complex, as people living in endemic areas exhibit a vast array of clinical states and immune responses. The Mongolian gerbil (Meriones unguiculatus)-B. pahangi model of human lymphatic filariasis has provided much information on immune parameters associated with filarial infection. Prior investigations in our laboratory have shown that gerbils closely mimic a subset of patients classified as microfilaremic but asymptomatic, a group that comprises the majority of people living in endemic areas. Worm recovery data suggest that gerbils carrying current B. pahangi infections do not show any resistance to subsequent subcutaneous B. pahangi infections. The aim of the present studies was to investigate the T cell cytokine response in gerbils receiving multiple infections of B. pahangi as a means of mimicking the conditions experienced by people in endemic areas. The T cell cytokine profile generated by multiply infected gerbils was not different from that previously generated by gerbils infected only once with B. pahangi. Gerbils infected multiple times with B. pahangi showed a transient increase in IL-5, which corresponded to the increased eosinophil levels previously reported from multiply infected gerbils. Chronically infected gerbils showed elevated IL-4 mRNA levels, as has been reported from gerbils infected only once with B. pahangi. Chronic infections were also associated with a state of immune hyporesponsiveness, as determined by the characterization of lymphatic thrombi and lymphoproliferation of spleen and renal lymph node cells to worm antigen.

Cytokine profiles of filarial granulomas in jirds infected with Brugia pahangi

Background

A granulomatous inflammatory response develops in jirds infected subcutaneously or intraperitoneally with filarial nematodes namely Brugia pahangi and B. malayi. Previous studies by light and electron microscopy have shown cellular inflammatory responses in and around these granulomas. Furthermore, the cellular inflammatory responses of granulomas found in the lymphatics and peritoneal cavity appear to be similar. The purpose of this study was to determine the cytokine profiles of granulomas in the peritoneal cavity of B. pahangi-infected jirds and to determine whether the granulomas release any proinflammatory cytokines ex vivo.

Methods

A semiautomated quantitative polymerase chain reaction (Q-PCR) was performed on cDNA prepared from the granulomas of infected jirds to study the species-specific mRNA expression of IL-2, IL-4, IFN-γ, IL-5, and IL-10. Genomic DNA was extracted from the granulomas, and parasite DNA was detected by Q-PCR by amplifying the HhaI repeat sequence. The levels of the inflammation-causing cytokines IL-6 and TNFα that were secreted by the granulomas were measured by cell-based assays.

Results

Florid granulomas showed higher levels of IFN-γ than other cytokines, linking this Th1 cytokine to the granulomatous inflammation that develops in jirds and humans. IL-4 expression was much lower than that of IFN-γ but higher than that of IL-10. A low level of IL-5 mRNA expression was detectable in all granulomas as was the level of IL-2 expression. The levels of the inflammatory cytokines IL-6 and TNFα, secreted by intact granulomas, spontaneously increased by 48 h after culture. Parasite antigen stimulation and subsequent release of IL-6 and TNFα by the granulomas indicated a moderate increase in the levels of these two cytokines. The amplification of the Brugia HhaI repeat DNA and Wolbachia 16S rDNA indicated worm components and bacterial components in the granulomatous tissue.

Conclusion

Granuloma development in filarial infections is a complex process involving cellular reactions responding to parasite/bacteria and their components. The interactions between worm-derived granulomas and their hosts are dynamic and multifaceted. The data collected thus far suggest that the expression profiles of many of the measured cytokines in the lymphoid tissues of Brugia-infected jirds are different from those of the cytokines in granulomas. Moreover, granulomas have the ability to secrete the inflammatory cytokines IL-6 and TNFα.

Kinetics of T cell cytokine gene expression in gerbils after a primary subcutaneous Brugia pahangi infection

The majority of patients infected with lymphatic filariae are microfilaremic but tend to manifest little obvious pathology because of the infections. Data collected from the Mongolian gerbil-Brugia spp. model for human lymphatic filariasis suggest this experimental animal model system most closely represents this patient group and will be useful in studying immunological parameters associated with chronic infections. This article reports the quantitation of interleukin (IL)-4, IL-5, IL-10, IL-13, and interferon (IFN)-gamma messenger RNA (mRNA) in gerbils after a primary subcutaneous infection with Brugia pahangi. Chronically infected gerbils showed elevated IL-4 in all tissues, compared with earlier time points, linking this Th2 cytokine to the downregulation of responsiveness, which develops in gerbils and humans. Both IL-5 and IL-13 mRNA expression were transient in all tissues. The peak in IL-5 at 14-28 days postinfection reflects the peak of peripheral eosinophilia observed in B. pahangi-infected gerbils. Little IFN-gamma mRNA was reported from chronically infected gerbils. The data collected thus far suggest that the expression profile of many of the measured cytokines in B. pahangi-infected gerbils reflects what is seen in an important subset of humans infected with lymphatic filariae, the microfilaremic, asymptomatic patient.

Toward an understanding of the interaction between filarial parasites and host antigen-presenting cells

Lymphatic filarial infection, from an immunologic point of view, is one of the most complex parasite infections. Not only are there different clinical manifestations that reflect differing immune responses, but the parasite's multiple stages, each with distinct anatomic tropism, add a compartmental layer of complexity to an already complicated process. Moreover, these parasites have finely tuned immune evasion strategies that enable escape from the innate immune system. As different stages of the parasite interact with different types of antigen-presenting cells that, in turn, may play a significant role in shaping the subsequent adaptive immune response, the focus of this review is to provide insight into the interaction between filarial parasites and antigen-presenting cells with an eye toward understanding how they influence parasite antigen-driven T-cell responses.

Construction of DNA vaccines and their induced protective immunity against experimental Eimeria tenella infection

In an attempt to construct a DNA vaccine against chicken coccidiosis, the TA4 gene of Eimeria tenella strain BJ was ligated to the mammalian expression vector pcDNA3.1/Zeo(+) to give pcDNA3.1-TA4 (pcDT). Then, Et1A (E. tenella refractile body gene) was ligated to it, upstream, aiming to be expressed in fusion with TA4, giving pcDNA3.1-Et1A-TA4 (pcDET). The constructed DNA vaccines were given to broilers intramuscularly 10-15 min after the breasts had been pre-treated with 25% sucrose solution. At 7 days after the second vaccination, chickens were challenged with 3 x 10(4) sporulated oocysts of E. tenella BJ. The chickens were killed and the lesion scores of the ceca, the relative body-weight gains and the numbers of oocysts in the ceca of each group of chickens were calculated at day 8 post-inoculation. Results indicated that both pcDT and pcDET could induce protective immunity against coccidial challenge. Their use could obviously reduce oocyst output and alleviate chicken body-weight decrease due to coccidial infection. An anti-coccidial index of 160 was achieved with a treatment of 50 microg pcDET and 100 microg pcDT.

Proinflammatory Cytokines Dominate the Early Immune Response to Filarial Parasites

Although the early human immune response to the infective-stage larvae (L3) of Brugia malayi has not been well-characterized in vivo (because of the inability to determine the precise time of infection), the consensus has been that it must involve a predominant Th2 environment. We have set up an in vitro system to study this early immune response by culturing PBMC from unexposed individuals with live L3 of B. malayi. After 24 h of culture, T cell responses were examined by flow cytometry and by quantitative real-time RT-PCR for multiple cytokines. T cells were activated early following exposure to L3 as indicated by up-regulation of surface markers CD69 and CD71. The frequency of T cells expressing proinflammatory Th1 cytokines (IFN-gamma, TNF-alpha, GM-CSF, IL-1alpha, and IL-8) but not Th2 cytokines (IL-4, IL-5, IL-6, IL-10, and IL-13) was significantly increased in response to L3. This T cell response occurred in both the CD4 and CD8 T cell compartment and was restricted to the effector/memory pool (CD45RO(+)). This T cell response was not due to LPS activity from the parasite or from its endosymbiont, Wolbachia; moreover, it required the presence of APC as well as direct contact with live L3. Real-time RT-PCR analysis of multiple cytokines in the T cells confirmed the increased expression of proinflammatory Th1 cytokines. Up-regulation of these cytokines suggests that the primary immune response to the live infective stage of the parasite is not predominantly Th2 in nature but rather dominated by a proinflammatory response.

Elevated immunoglobulin E against recombinant Brugia malayi gamma-glutamyl transpeptidase in patients with bancroftian filariasis: association with tropical pulmonary eosinophilia or putative immunity

A major allergen of the lymphatic filarial nematode Brugia malayi, a homologue of gamma-glutamyl transpeptidase (gamma-GT), is involved in the pathology of tropical pulmonary eosinophilia (TPE) through its potent allergenicity and the induction of antibodies against the host pulmonary epithelium. To investigate the immunoglobulin G (IgG) subclass and IgE responses to recombinant B. malayi gamma-GT, we analyzed the results obtained from 51 patients with differing clinical manifestations of bancroftian filariasis. gamma-GT-specific IgG1, rather than IgG4, was the predominant IgG subclass, particularly in patients with TPE (geomean, 6,321 ng/ml; range, 78 to 354,867 ng/ml) and was 75 times higher than in patients with elephantiasis (CP) (P < 0.003) and 185 times higher than in endemic normal individuals (ENL) (P < 0.010). IgG2 responses were low and IgG3 was almost absent, with no significant differences among the groups. gamma-GT-specific IgG4 responses were significantly elevated in those with subclinical microfilaremia (MF) compared to the CP and ENL groups and correlated with the presence of circulating filarial antigen (CAg). More significantly, gamma-GT-specific IgE antibody levels were strikingly elevated in patients with TPE (geomean, 681 ng/ml; range, 61 to 23,841 ng/ml) and in the ENL group (geomean, 106 ng/ml; range, 13 to 1,405 ng/ml) whereas the gamma-GT-specific IgE level was 44 and 61 times lower in those with MF and CP, respectively (P < 0.001). Elevated gamma-GT-specific IgE/IgG4 ratios were demonstrated in patients with TPE (ratio, 45) and ENL (ratio, 107). Because expression of gamma-GT in Brugia infective third-stage larvae (L3) was demonstrated by immunoblot analysis, the elevated gamma-GT-specific IgE antibodies appear to be associated not only with pulmonary pathology but also with possible resistance to infection in lymphatic filariasis.

Brugia pahangi and Wolbachia: the kinetics of bacteria elimination, worm viability, and host responses following tetracycline treatment

Wolbachia spp., first reported from filariae nearly 30 years ago, have been suggested to contribute to the pathogenesis associated with human filarial infection. Tetracycline has been used to cure filariae of Wolbachia, as a novel means of chemotherapeutic treatment for both ocular and lymphatic filariasis. Tetracycline treatment of L4 or adult Brugia pahangi in vivo resulted in Wolbachia clearance. Less tetracycline was required to clear Wolbachia when treatment began at the L4 stage, compared with adults. Female worms died earlier than male worms when tetracycline was administered at the L4 stage. In all cases, Wolbachia clearance was closely associated with worm death. Worm recoveries decreased following the L4-L5 molt, suggesting tetracycline does not interrupt molting in this model system. Despite worm death and the assumed release of both bacterial- and worm-derived molecules, differences in inflammatory cell population and T cell cytokine mRNA profiles were negligible between tetracycline-treated and non-treated B. pahangi infected gerbils. These data suggest the contribution of Wolbachia to the in vivo induction of the gerbil immune response to B. pahangi may be small.

Wolbachia in filarial nematodes: evolutionary aspects and implications for the pathogenesis and treatment of filarial diseases

The presence of intracellular bacteria in the body of various species of filarial nematodes, including important parasites such as Brugia malayi, Dirofilaria immitis, and Onchocerca volvulus, was observed as early as the mid-1970s. These bacteria were shown to be transovarially transmitted (from the female worm to the offspring) and to be present in significant amounts in the body of the nematode. As highlighted by their discoverers, the potential importance of these bacteria is fairly obvious: (1) bacteria-derived molecules should be considered as having an immunological and pathological role in filarial diseases; (2) the interaction between the bacteria and the filarial host deserves investigation, in view of the possibility that the bacteria are needed by the host nematode and could thus represent a target for therapy. Other authors, independently from the discovery of these intracellular bacteria, showed that the antibiotic tetracycline (which is well known for its efficacy on intracellular bacteria) had detrimental effects on two species of filarial nematodes (Brugia pahangi and Litomosoides sigmodontis). It is therefore surprising that for more than 20 years, no further investigations focused on the bacteria of filarial nematodes, nor on the anti-filarial properties of tetracycline. Recently, the bacteria of filarial nematodes have been independently "rediscovered" by research groups from the schools of Hamburg, Liverpool and Milan. These bacteria are now classified as Wolbachia, and the basic aspects of their phylogenetic history and relationship with the Wolbachia of arthropods have been reconstructed. In addition, their implications for the pathogenesis and treatment of filarial diseases have started to be uncovered. This paper, which is authored by representatives of the three European schools who reopened this research area, reviews our present knowledge of these fascinating microorganisms, highlighting the complexity of a symbiotic system which involves, in addition to the nematode and its bacterium, the vertebrate host.

Regulation of the immune response in lymphatic filariasis: perspectives on acute and chronic infection with Wuchereria bancrofti in South India

Delineating the immune responses in lymphatic filariasis has been complicated not only by the rapidly expanding knowledge of new immunological mediators and effortors, but also by new methodologies (in particular, circulating filarial antigen detection) for defining and categorizing filarial-infected individuals. By using assays for circulating antigen in the sera collected as part of the many immunological studies performed on individuals in a Wuchereria bancrofti-endemic region of South India, we have attempted to explore the influence of patency on the antigen-driven proliferative and cytokine responses seen in peripheral blood mononuclear cells of individuals with varying clinical manifestations of lymphatic filarial infection. Moreover, we have provided perspectives on the differences between acute and chronic infection with W. bancrofti and suggested mechanisms that may underly the modulation of the immune response as patency occurs.

Divergent roles for macrophages in lymphatic filariasis

Macrophages have long been recognized as important cells associated with filarial infection but their function as effectors and/or suppressors has not been elucidated. Recent advances in our understanding of the role that macrophages may play in lymphatic filariasis have come from in vitro studies and mouse models of filarial infection. Based on these new findings, we hypothesize that while dead or dying worms induce the 'classical' activation of macrophages and a subsequent pro-inflammatory response, live and healthy worms secrete products that induce type 2 cytokines and the differentiation of 'alternatively' activated macrophages that downregulate an inflammatory response. Thus, the balance between the 'classical' and 'alternative' activation pathways of macrophages could be an important factor in inflammatory pathology associated with filariasis.

Transmission intensity and human immune responses to lymphatic filariasis

Our understanding of how the host immune response influences the risk of developing disease has changed dramatically over the past decade. Previously, the spectrum of disease associated with lymphatic filariasis was largely attributed to the nature of the host immune response. Now, we appreciate that the duration and intensity of infection and possibly the direct influence of parasite-derived molecules also determine the risk of disease. Individuals chronically infected with lymphatic filariasis generally have an impaired lymphocyte proliferation response to filarial antigens and favour Th2-type cytokine responses. This ability to down-modulate the host immune response may help protect the host from disease. Defects in antigen-presenting cell (APC) function appear to participate in this acquired immune hyporesponsiveness, although the mechanisms as to how this occurs are poorly understood. Here, we present evidence that repeated exposure to infective stage larvae and their secreted products may stimulate basophils and mast cells to related products that may impair APC function.

Are inflammation and immunological hyperactivity needed for filarial parasite development?

Immune-dependent growth and development of infectious agents and pathogenesis of disease are increasingly being recognized. It is proposed that the development of filarial larvae to adult stage parasites takes place in an ambiance of inflammatory T helper cell type 1 cytokines in mammalian hosts, and that susceptibility to filarial infections could be governed by the status of macrophage-derived nitric oxide and host ability to produce antibodies to filarial T-independent (carbohydrate) antigens.

Brugia pahangi: quantitative analysis of infection in several inbred rat strains

We report a comprehensive study of the infectivity of Brugia pahangi in male and female rats of eight different inbred strains. A single infection of any inbred rat strain will produce rats that become microfilaremic, have occult infection, or clear the primary infection. The proportion belonging to any category is determined by the basic susceptibility level of that strain. Patency rates (blood microfilaria+) ranged from 24% (AO rats) to 73% (WKA rats). The period for which microfilaria were in the circulation was directly related to microfilarial burden, with rats carrying less than 50 mf/ml of blood patent for 11.8 weeks +/- 12.2; for 50-499 mf/ml it was 37.6 +/- 14.8 and for 500+ mf/ml it was 63.3 +/- 34.2 weeks. Suckling rats were resistant to infection (0 patent) and weanlings were intermediate in resistance between suckling and adult rats. Female rats were highly resistant to infection. Approximately half of amicrofilaremic rats have occult infections. A high proportion of patent infections involve the testes or testicular lymphatics. In the most susceptible rat strains, more than 95% of the administered L3 or developing L4 parasites were killed within 28 days. During the course of the first 6 months, the ratio of males to females fell significantly, suggesting a shorter life span in male worms. The features of the infectivity/patency patterns in rats are compared with recognized patterns obtaining in human populations. We conclude that rats provide a valuable and underutilized model for the experimental analysis of filarial infections.

Requirement for In Vivo Production of IL-4, But Not IL-10, in the Induction of Proliferative Suppression by Filarial Parasites

Loss of T lymphocyte proliferation and the emergence of a host response that is dominated by a Th2-type profile are well-established features of human filariasis. We have previously reported that adherent peritoneal exudate cells (PEC) from mice transplanted with adult Brugia malayi parasites suppress the proliferation of lymphocytes without blocking Ag-cytokine production in vitro. We now show that infection of mice with the infective larval (L3) stage of B. malayi generates a similar population of PEC. Suppressive cells are generated within 7 days of infection and mediate their effects through a nitric oxide-independent pathway. Both L3 and adult infection elicit high levels of host IL-4 whereas the microfilarial stage of the parasite induces IFN-γ production and does not generate a similar form of suppression. Production of host IL-4 was necessary to allow the generation of suppressive PEC, given that IL-4-deficient mice implanted with adult parasites failed to induce proliferative block. However, IL-10-deficient mice implanted with adult parasites resulted in T cell suppression, indicating that IL-10 is not essential for the induction of hyporesponsiveness. Neither IL-4 nor IL-10 were directly responsible for ablating cellular proliferation in vitro, as the addition of neutralizing Ab to either cytokine did not reverse the proliferative block. Thus, IL-4 produced in vivo in response to filarial L3 and adult parasites is essential for the induction of proliferative suppression but is not itself the suppressive factor.

Requirement for In Vivo Production of IL-4, But Not IL-10, in the Induction of Proliferative Suppression by Filarial Parasites

Loss of T lymphocyte proliferation and the emergence of a host response that is dominated by a Th2-type profile are well-established features of human filariasis. We have previously reported that adherent peritoneal exudate cells (PEC) from mice transplanted with adult Brugia malayi parasites suppress the proliferation of lymphocytes without blocking Ag-cytokine production in vitro. We now show that infection of mice with the infective larval (L3) stage of B. malayi generates a similar population of PEC. Suppressive cells are generated within 7 days of infection and mediate their effects through a nitric oxide-independent pathway. Both L3 and adult infection elicit high levels of host IL-4 whereas the microfilarial stage of the parasite induces IFN-γ production and does not generate a similar form of suppression. Production of host IL-4 was necessary to allow the generation of suppressive PEC, given that IL-4-deficient mice implanted with adult parasites failed to induce proliferative block. However, IL-10-deficient mice implanted with adult parasites resulted in T cell suppression, indicating that IL-10 is not essential for the induction of hyporesponsiveness. Neither IL-4 nor IL-10 were directly responsible for ablating cellular proliferation in vitro, as the addition of neutralizing Ab to either cytokine did not reverse the proliferative block. Thus, IL-4 produced in vivo in response to filarial L3 and adult parasites is essential for the induction of proliferative suppression but is not itself the suppressive factor.

Brugia pahangi: differential induction and regulation of jird inflammatory responses by life-cycle stages

It has been hypothesized that different life-cycle stages of filarial nematodes induce different host responses. This concept was examined in the Brugia pahangi-jird model of lymphatic filariasis by measuring the kinetics of inflammatory responses to parasite antigens following intraperitoneal inoculation of different life-cycle stages. For this purpose, viable female or male worms, L3, L4, or microfilarial stage, were used. Dead worms served as controls. Worm and microfilarial burdens, pulmonary granulomatous inflammation (PGRN) to soluble adult worm antigen (SAWA)-coated beads, and peritoneal eosinophil and macrophage numbers were assessed at different days post-inoculation. All jirds inoculated with any of these life-cycle stages developed an early PGRN to SAWA which was later significantly reduced. Only viable worms induced down-regulation of the PGRN response. These results indicate that the hyporesponsive state is induced and maintained by all life-cycle stages. Also, the degree of granulomatous response was influenced by worm burden, with larger worm burdens inducing lower initial levels of PGRN to SAWA. Peritoneal inflammatory responses differed from the systemic response in that numbers of macrophages increased with time and microfilarial accumulation. No correlation was observed between peritoneal inflammatory responses measured by eosinophil and macrophage numbers and PGRN to SAWA.