Parasite-induced suppression of the immune response in Aedes aegypti by Brugia pahangi

The melanization response against intrathoracically inoculated Brugia pahangi and Dirofilaria immitis microfilariae (mff) isolated from vertebrate host blood was evaluated in both uninfected Aedes aegypti black-eyed Liverpool strain and in mosquitoes harboring a developing B. pahangi infection. The immune response against inoculated mff of either species was significantly reduced by 28-47% in infected as compared with uninfected mosquitoes. Attempts to passively transfer this suppression factor(s) by inoculating naive mosquitoes with 0.1-0.2 microliter of hemolymph from B. pahangi-infected mosquitoes produced equivocal results. The role this parasite-induced immune suppression might play in aiding parasite survival in compatible vectors is discussed.

Mansonella ozzardi in Haiti. IV. Evaluation of antibody reactivity to heterologous antigens

Sera from individuals in an area of Haiti endemic for Mansonella ozzardi were analyzed for reactivity to antigens of Brugia pahangi, Dirofilaria immitis, Mansonella llewellyni or Ascaris lumbricoides using either an enzyme-linked immunosorbent assay or an indirect immunofluorescent antibody test. IgM and IgG reactivity to all antigens was observed with sera from both microfilaremic and amicrofilaremic individuals when compared to reactivity of sera from individuals from nonendemic areas. Antibody reactivity to B. pahangi was greater than that to other antigens. IgG reactivity of sera from endemic patients to filarial antigens was consistently greater than that of IgM. Antibody reactivity was not correlated with age or microfilarial density.

IgE responses in human filariasis. IV. Parallel antigen recognition by IgE and IgG4 subclass antibodies

Immediate hypersensitivity responses are highly modulated in filariasis, and with few exceptions, the majority of infected individuals do not develop allergic manifestations. One possible mechanism for this modulated responsiveness could involve the high levels of IgG "blocking antibodies" shown to be present in filariasis and other chronic helminth infections. When immunoblot analyses were done to analyze the immunoglobulin (Ig) E and IgG antibody responses of patients simultaneously, remarkable similarity in the patterns of antigen binding was observed. In this study, the four IgG subclasses were analyzed in a similar manner in relation to IgE. The results clearly demonstrate that IgG4 was primarily responsible for this "parallel" recognition that was seen previously between IgG and IgE antibodies. These results lend additional support to the possibility that IgG4 may play an important role in modulating IgE-mediated allergic responses in vivo.

Induction of protection against Brugia malayi infection in jirds by microfilarial antigens

The development of immunologic methods to reduce transmission of human lymphatic filariasis depends on measures that will enhance the host's ability to eliminate infective larvae, adult worms, or blood-borne microfilariae (mf). The present study was designed to assess the capacity of a crude extract of Brugia malayi mf to decrease the level of microfilaremia and adult worm burden in jirds inoculated with infective larvae, and to identify the filarial antigens that elicit antibody responses in these animals. Thirty weeks after subcutaneous inoculation with 75 infective larvae, 100% of control jirds were patent (i.e., had microfilaremia) compared with 60% of the group immunized with 10 micrograms of crude microfilarial extract (p less than 0.05). In addition, microfilaremia was lower in patent immunized animals compared with controls (p less than 0.05). The mean total number of adult female B. malayi per jird recovered at necropsy in control animals was 16.0 vs 7.0 in immunized jirds (p less than 0.05). Serum of immunized jirds contained anti-mf antibodies with an end titer of 1:8000, a value similar to that of animals with chronic B. malayi infection. Microfilarial antigens of Mr approximately 150,000, 75,000, 42,000, and 25,000 were identified in immunoblotting studies by reactivity with antibodies in sera of immunized jirds. Antibodies induced by immunization with microfilarial extract were not specific for this stage of the parasite life cycle, as jird anti-mf antibodies reacted with a Mr approximately 150,000 and several Mr 50,000 to 110,000 antigens derived from immature and mature adult parasites of both sexes. These data indicate that immunization of jirds with a water soluble microfilarial extract enhances the host's ability to eliminate adult worms and blood-borne mf. The filarial antigens that induce antibodies in immunized jirds have been identified.

Molecular characterization of antigens of lymphatic filarial parasites

Three species of filarial worms,Wuchereria bancrofti, Brugia malayiandBrugia timori, are the causative agents of lymphatic filariasis in man, defined by the characteristic tropism of adult worms of each species for the afferent lymphatics. Reproductive activity leads to the release of large numbers of microfilariae, which circulate in the vascular system, and upon ingestion by an appropriate mosquito vector, develop through to infective third-stage larvae (L3) within 10–14 days. After a subsequent bloodmeal, the infective larvae enter the definitive host via the wound and mature to the adult stage over several months, involving two moults, during which the entire nematode exoskeleton (cuticle) is replaced.

Antibody and cellular immune responses to microfilarial antigens in ferrets experimentally infected with Brugia malayi

Eleven of 15 ferrets experimentally infected with Brugia malayi became amicrofilaremic after a brief patency; only four ferrets remained patent after 6 months of infection and two of these ferrets developed a high, persistent microfilaremia. Blastogenic responses of peripheral blood lymphocytes to antigens of microfilariae (mf), assayed in vitro, demonstrated an antigen sensitivity at prepatent, patent and postpatent periods of infection. Lymphocytes from ferrets with high microfilaremia had elevated background responses in culture which were directly correlated with the number of circulating mf. This background response was attributed to antigenic stimulation by mf present in the lymphocyte cultures; addition of mf to cultures of lymphocytes from postpatent ferrets induced responses equivalent to those observed in microfilaremic ferrets. Lymphocyte responses to the mitogen, concanavalin A, did not differ significantly among microfilaremic, amicrofilaremic and uninfected ferrets. Antibody in IgG to antigens of mf measured by ELISA and by immunoblots from SDS-PAGE showed similar patterns of response in ferrets which became amicrofilaremic and in the few ferrets which remained microfilaremic. prausnitz-Kustner tests demonstrated no consistent differences in titers to microfilarial antigens between patent and amicrofilaremic ferrets. The results suggest a high level of immune responsiveness to antigens of mf in infected ferrets with no evidence of immunosuppression associated with prolonged microfilaremia or of major changes in immune responses with development of amicrofilaremic infections.

Expression of cross-reactive surface antigens by microfilariae and adult worms of Brugia pahangi during infections in cats

Microfilariae of Brugia pahangi were labelled with 125-Iodine using the reagent IODOGEN. Electron microscope autoradiographs of sections of iodinated microfilariae showed that the label was strictly confined to their sheath. Adult worms were also iodinated by the same procedure. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis of detergent extracts of radio-labelled parasites revealed components of molecular weights 113, 81-71, 46 and 33 kDa in microfilariae, and of molecular weights 29, 20 and 16 kDa in adult worms. All but the 33 kDa component of microfilariae were immunoprecipitable with sera of infected cats and therefore antigenic. Antibodies to the 81-71 kDa and the 46 kDa microfilarial antigens were detected by immunoprecipitation before patency. Similarly, the 29 kDa antigen of adult worms was immunoprecipitable before the fourth moult. Therefore, during infection in cats, these antigens cross-react with epitopes present on earlier developmental stages.

Microfilariae of Brugia malayi contain a T cell mitogen

We investigated the mechanisms that lead to polyclonal hypergammaglobulinemia in persons exposed to or infected with lymph-dwelling filarial parasites. Extracts of microfilariae of Brugia malayi induce the in vitro proliferation of lymphocytes from nonsensitized donors. The mitogenic factor(s) responsible for this effect is of low molecular weight (Mr) and acts on T4+ cells but not on T8+ T lymphocytes or on B cells. T4+ lymphocytes stimulated with filarial mitogen augment the in vitro production of immunoglobulins by autologous B lymphocytes.

Cellular immune competence in bancroftian filariasis

Lymphocyte proliferative responses to homologous and heterologous filarial antigens, mitogens and purified protein derivatives (PPD) were analysed in a group of 37 subjects from an area endemic for bancroftian filarial infection. The majority of the subjects without any clinical or parasitological evidence of filariasis (endemic normals) reacted with homologous microfilarial antigens only. Non-treated patients with patent microfilaraemia, did not respond to homologous of heterologous microfilarial antigens. In contrast, diethylcarbamazine (DEC)-treated microfilaraemic patients, reacted with homologous filarial antigens. Patients with elephantiasis reacted to microfilarial and adult worm antigens. Response to PPD was marginally depressed in patent microfilaraemic patients and a rise was observed in elephantiasis cases. Endemic normals exhibited normal response to PPD. Responses to mitogens were depressed throughout the course of the infection.

Differential pathogenicity of Brugia malayi, B. patei and B. pahangi in immunodeficient nude mice

Immunodeficient nude mice chronically parasitized by subperiodic Brugia malayi developed an elephantoid appearance with persistent lymphoedema of limbs and massive lymphangiectasis of subcutaneous vessels containing viable adult worms. Removal of worms reversed the process. The syndrome was not caused by B. patei or B. pahangi and was not correlated with the presence or absence of microfilaremia. Histologic examination of elephantoid mice revealed dilated and tortuous lymphatics containing small nonobstructive lymph thrombi composed of small mononuclear cells and multinucleate giant cells. Draining lymph nodes were not enlarged or congested and mast cells in oedematous tissue were not degranulated. Analysis of lymph aspirated from dilated lymphatics showed increased total protein content: bacterial sepsis was not detected. This work suggests that viable adult B. malayi exert direct pathologic effects upon lymphatics and that this parasite is more pathogenic than related Brugia spp.

Specificity of surface molecules of adult Brugia parasites: cross-reactivity with antibody from Wuchereria, Onchocerca and other human filarial infections

The extent of structural and immunological similarity between surface antigens of three species of Brugia filarial parasites was studied by lodogen-mediated surface labelling of adult worms of B. malayi, B. pahangi and B. timori. The close homology and cross-reactivity between these antigens reported in previous surface labelling studies with Bolton-Hunter reagent, was verified in this system. The surface antigens of adult B. pahangi are also recognised by antibody from patients with Wuchereria bancrofti, the major human lymphatic filariae, and by antibody to Loa loa and Mansonella perstans. Further experiments have begun to establish the boundaries of these cross-reactions: antibodies to nonfilarial nematodes such as Trichinella, Necator and Strongyloides does not recognise the adult surface antigens; however, although most anti-Onchocerca sera show little or no reaction to the major (29 kDa) surface antigen, there is consistent reactivity to the secondary 20 kDa antigen, and extensive recognition of a minor antigen of 15 kDa.

Secreted and circulating antigens of the filarial parasite Brugia pahangi: analysis of in vitro released components and detection of parasite products in vivo

A range of excretory-secretory (ES) antigens have been characterised following in vitro culture of adult Brugia pahangi filarial nematodes in serum-free medium. Analysis by radioiodination, sodium dodecyl sulfate polyacrylamide gel electrophoresis, and immunoprecipitation of purified macromolecules with antibodies from human and experimental animal infections reveals both host and parasite components. Two host molecules appear by molecular weight and immunoprecipitation analysis to be immunoglobulin and serum albumin, presumed to be taken up from the jird host from which adult worms were recovered. A further prominent component, of 19 kDa, reacts with neither anti-host nor anti-filarial antibodies, and may represent a non-immunogenic parasite product. Three additional bands, although less intensely radiolabelled, did prove to be consistently antigenic, with apparent molecular weights of 15, 29 and 40 kDa. A further ES antigen, which does not take up radio-iodine or lend itself to electrophoretic analysis, has also been detected. This molecule reacts in a immunoradiometric assay in which monoclonal antibody directed against a repetitive epitope acts both to capture and indicate antigen presence. The same antibody, Bp-1, may also be employed to detect circulating antigen in the serum of animals experimentally infected with Brugia pahangi, and in the serum of patients with each of the three species of human lymphatic filariasis, Brugia malayi, Brugia timori and Wuchereria bancrofti.

Brugia malayi: vaccination of jirds with 60cobalt-attenuated infective stage larvae protects against homologous challenge

Vaccination of inbred jirds (Meriones unguiculatus) with 60cobalt radiation-attenuated Brugia malayi infective stage larvae (L3) protected against homologous challenge given either subcutaneously (sc) or by the intraperitoneal (ip) route. Groups of jirds vaccinated once sc with 75, 15 Krad L3 showed from 69% to 91% reduction in recovered worms after ip challenge infection compared to infection in non-vaccinated control jirds, while 75% reduction in mean worm burden was seen in jirds receiving sc challenge infection. A single sc vaccination with 75, 10 or 20 Krad L3 produced no protection (10 Krad) and 64% reduction in recovered worms (20 Krad). Therefore the 15 Krad dose appeared to be best. A marked increase in anti-B. malayi antibody in vaccinated jirds was seen (by ELISA) immediately after challenge infection and an immunofluorescence assay showed that L3 incubated in serum from vaccinated jirds were completely and uniformly covered with specific antibody. Eosinophil-rich granulomas containing dead and moribund L3 were recovered from vaccinated jirds. This model of protective immunity in a Brugia-susceptible small rodent may provide a useful system for identification of molecularly defined filarial-protective immunogens.

Application of immunoassay methods in the serodiagnosis of human filariasis

To be more definitive as a serodiagnostic method, an ideal immunoassay for detection of filaria-specific antibody and filarial antigens in body fluids should identify active filarial infection and differentiate between past and present infection. It should perform well in the areas of precision, reproducibility, parallelism, and sensitivity and should use reference and quality control reagents prepared with human body fluids that contain defined amounts of filarial antigen. Moreover, a sufficient quantity of reference serum in stable form should be made available to permit interlaboratory cross-standardization. Difficulty with uniform radiolabeling of filarial antigen extracts and the interference of human antibody have combined to eliminate the competitive-binding immunoassay as a useful method. Of the noncompetitive methods evaluated, the immunoradiometric assay (IRMA) and its nonisotopic counterpart, the immunoenzymetric assay (IEMA), perform best. As a factor masking diagnostically important antigenic determinants, the variable amount of human antibody in blood interfered with all assay designs tested. Better characterization of the antigen(s) circulating in the blood or excreted into the urine of infected individuals will improve assay specificity and sensitivity and will facilitate the preparation of antibody probes more specifically targeted to filarial antigens for use in both the IRMA and IEMA.

Serum dependent cell-mediated immune reactions to Brugia pahangi infective larvae

Fresh normal rat serum (fNRS) promoted adherence and cytotoxicity of albino rat neutrophils and macrophages to Brugia pahangi infective larvae (L3) in vitro. EDTA and not EGTA abolished the adherence activity suggesting the involvement of complement components via the alternate pathway. C3 molecules were detected on the surface of the parasite by immunofluorescence. fNRS depleted of complement by treatment with Zymosan A or of factor B by heating at 50 degrees C for 20 min, failed to promote cell adherence to the parasite. fNRS and cells from albino rat were more potent in inducing cytotoxicity to L3 than those from jird or Mastomys which may reflect the greater resistance offered by the albino rat to B. pahangi infection. In the presence of IgG and a heat labile factor, possibly complement, of immune serum, neutrophils and macrophages and to a lesser extent eosinophils adhered to and killed the larvae. Immune sera raised against microfilariae of different filarial parasites promoted cell-mediated cytotoxicity to B. pahangi L3 suggesting sharing of antigens between the two stages.

Brugia malayi: intravenous injection of microfilariae in ferrets as an experimental method for occult filariasis

Microfilaremia, immune responses, and pathology were compared in ferrets infected with 100 third-stage larvae of Brugia malayi (subperiodic strain) or injected intravenously with 10(6) microfilariae. Ferrets (Mustela putorius furo) inoculated with third-stage larvae typically became patent during the third month after infection, with a mean patency of 123 +/- 25 (SE) days. Ferrets injected intravenously with microfilariae exhibited a relatively constant microfilaremia for 3-4 weeks and usually cleared microfilariae before the fourth month. Ferrets that cleared microfilariae after intravenous injection of microfilariae or after infection with third-stage larvae failed to become patent or became amicrofilaremic within 3 weeks after a challenge intravenous injection of 10(6) microfilariae. Clearance of circulating microfilariae was associated with eosinophilia and serum antibody specific for the microfilarial sheath in ferrets injected with microfilariae and in most ferrets infected with third-stage larvae. Ferrets infected with third-stage larvae and necropsied after clearance of microfilariae had tissue inflammatory reactions to microfilariae characteristic of occult filariasis (tropical eosinophilia) in man; these ferrets exhibited immediate cutaneous hypersensitivity and circulating reaginic antibody to antigens of microfilariae. In ferrets necropsied following two intravenous injections of microfilariae, the majority of ferrets examined within 10 days after clearance of microfilariae had visible liver lesions to microfilariae identical to those of the ferrets infected with third-stage larvae; immediate cutaneous hypersensitivity and reaginic antibody were not consistently detected in ferrets injected with microfilariae. Sera from ferrets that had cleared circulating microfilariae were transferred passively into ferrets made microfilaremic by intravenous injection of microfilariae. Sera with microfilarial sheath-reactive IgG antibody titers (greater than or equal to 1:200) and microfilarial agglutination titers (greater than or equal to 1:40) rapidly cleared injected microfilariae (less than 24 hr); this serum also cleared or greatly reduced circulating microfilariae established by an infection with third-stage larvae; only the IgG-containing fraction of the sera was active in immune clearance. Sera that cleared microfilariae of B. malayi did not clear circulating microfilariae of Dirofilaria immitis or prevent recurrence of circulating microfilariae of B. malayi in ferrets infected with adult filariae.(ABSTRACT TRUNCATED AT 400 WORDS)

IgE responses in human filariasis. III. Specificities of IgE and IgG antibodies compared by immunoblot analysis

IgE and IgG immune responses were qualitatively characterized in three well-defined groups of patients with different clinical manifestations of lymphatic filariasis caused by infection with Wuchereria bancrofti; viz. tropical pulmonary eosinophilia (TPE), chronic lymphatic obstruction with elephantiasis (CP), and asymptomatic microfilaremia (MF). A complex filarial antigen preparation extracted from adult filarial parasites was separated on SDS-polyacrylamide gels, and was electrophoretically transferred to nitrocellulose paper before being incubated with individual sera and being probed with radiolabeled anti-IgE or protein A. Three clinical groups of patients showed distinct patterns of antigen recognition by both IgE and IgG antibodies, with TPE patients showing the most diverse patterns and microfilaremic individuals the most restricted responses for both antibody isotypes. "Dual recognition" of antigens by IgE and IgG antibodies seemed to be the rule rather than the exception for each individual's immune response to the parasite antigens, but the relative magnitudes of IgG and IgE responses differed among the three groups. The ratio of IgG to IgE antibody was generally greater in patients with MF and CP than in those with TPE. These findings of the comparative specificities and relative abundance of IgE and IgG antibodies in infected patients may have fundamental importance in explaining the clinical expression (especially allergic reactivity) and disease pathogenesis of human filarial infections.

Activation of the alternative complement pathway in normal human serum by Loa loa and Brugia malayi infective stage larvae

Infective stage larvae (L3) of Loa loa and Brugia malayi upon in vitro incubation with normal human serum activated the alternative complement pathway. C3 conversion products were detected on larval cuticles by eosinophil adherence and by immunofluorescence with C3c antiserum. No evidence for cuticle binding of IgG, IgA, IgM, Clq, or C4 was found by immunofluorescence. L3-induced C3 activation was inhibited by 10 mM EDTA but unaffected by 10 mM Mg++-EGTA. Human sera deficient in C2, C4, or C6 incubated with L3 resulted in C3 activation. However, sera treated with zymosan or heated for 1 h, 56 degrees C were unreactive with L3. Immunoelectrophoresis of fresh serum exposed to L3 for 1 h at 37 degrees C showed C3 cleavage products. The results indicate that these nematode L3 activate the alternative complement cascade via cuticular surface components. Larval viability was unaffected by complement activation or by adherence of eosinophils.

An evaluation of different methods for labelling the surface of the filarial nematode Brugia pahangi with 125iodine

The specificity of a range of 125I labelling techniques (Chloramine T, Iodogen, Bolton and Hunter reagent, lactoperoxidase and iodosulfanilic acid) to the surface of the filarial nematode Brugia pahangi was evaluated by autoradiography of sections of labelled worms and of dried SDS-polyacrylamide gels following electrophoresis of homogenised worm extracts. It was concluded that Bolton and Hunter reagent was not surface specific but labelled proteins throughout the body of the worm. At the light microscope level autoradiography of worms labelled using Chloramine T, Iodogen, lactoperoxidase and iodosulfanilic acid demonstrated that the 125I labelling was restricted to the worm surface. Electrophoresis and autoradiography showed that each method produced a different pattern of labelled polypeptide. A polypeptide of molecular weight 30 kDa was labelled using each method except Bolton and Hunter reagent, and appears to be a major surface component.

Diethylcarbamazine-mediated clearance of Brugia pahangi microfilariae in immunodeficient nude mice

Congenitally athymic nude C3H/HeN mice, microfilaremic with Brugia pahangi, were treated with diethylcarbamazine citrate (DEC). A single oral dose (100 mg/Kg body weight) of DEC resulted in the rapid reduction of numbers of circulating microfilariae in nude, thymus-grafted nude and complement-depleted nude mice. Antibodies of the IgM and IgG isotypes were not detected in the serum of microfilaremic nudes or on the microfilarial surface. These results suggest that DEC-mediated clearance of microfilariae from the circulation of nude mice is probably independent of thymus-dependent immunological mechanisms.

Surface antigens of a filarial nematode: analysis of adult Brugia pahangi surface components and their use in monoclonal antibody production

The surface antigens of adult worms of the filarial nematode Brugia pahangi have been investigated further by surface radioiodination and detergent solubilisation techniques. In addition to yielding new information on the distribution of antigenic components of this stage, detergent-solubilised molecules were used in both radiometric and enzyme-linked assays for human and mouse antibody. These assays were subsequently used in screening for monoclonal antibodies from hybrid cells derived from animals infected with living parasites and boosted with detergent-extracted antigen. Three monoclonal antibody-producing cell lines were isolated, with differing antigenic specificities: Bp-1, which binds a non-iodinatable antigen with high ELISA activity; Bp-2, which reacts with a determinant found on but not unique to the major surface Iodogen-labelled 29 kDa antigen; and Bp-3, which is specific for a minor antigen of 20 kDa revealed by Iodogen labelling.

Resistance against Brugia malayi microfilariae induced by a monoclonal antibody which promotes killing by macrophages and recognizes surface antigen(s)

Several monoclonal antibodies were produced following the immunization of mice with infective larvae of Brugia malayi. One of these gives a positive fluorescence reaction on the surface of B. malayi microfilariae and this particular monoclonal antibody (IgM isotype) was able to mediate mouse peritoneal macrophage adherence to, and killing of, B. malayi microfilariae in vitro. Adherence and killing were enhanced by fresh normal mouse serum, suggesting a role for complement. When the same monoclonal antibody was passively transferred to mice harbouring microfilariae in their circulation, a complete clearance of microfilariae was observed in 70% of the animals. This monoclonal antibody was able to recognize antigenic determinants (of 110,000 MW) present on the surface of B. malayi microfilariae by radioimmunoprecipitation.

Brugia malayi: serum dependent cell-mediated reactions to microfilariae

Sheathed and exsheathed microfilariae of Brugia malayi are killed by normal rat cells in the presence of immune serum in vitro. Immune serum heated at 56 degrees C for 1 hour lost this activity which was largely restored by the addition of fresh normal rat serum. EDTA but not EGTA abolished this activity indicating the operation of complement by alternate pathway. Fresh normal rat serum alone promoted cellular adherence without exerting cytotoxicity to the microfilariae. The activity in the immune serum could be removed with Staphylococcus aureus cells containing Protein A or anti-IgG antiserum. The activity could also be absorbed to and eluted from Protein A--sepharose CL-4B suggesting the involvement of IgG. Neutrophils and macrophages participate in the antibody dependent cell-mediated cytotoxicity phenomenon. Eosinophils while adhering to the microfilariae exert cytotoxicity only to the exsheathed parasites.

Filarial parasite-specific T cell lines: induction of IgE synthesis

The development of T lymphocyte lines and clones of defined specificity has provided an important method for investigating T cell recognition of foreign antigens as well as T cell influence on B cell activity. We described previously a parasite-specific T cell line (TCL) derived from a patient with a naturally acquired filarial infection and elevated levels of serum IgE. The TCL is composed of Leu-3+ helper cells and is maintained independent of exogenous growth factors. In the present study, we used these T cells to investigate their immunoregulatory function on the in vitro IgE response. These parasite-specific T cells can provide isotype-specific help for antigen-induced IgE production by B cells in vitro. Autologous T cells profoundly suppress IgE production in a concentration-dependent manner. Furthermore, soluble factors generated from these filarial-specific TCL after antigen stimulation are able to induce the production of IgE in normal human cells not already synthesizing measurable amounts of IgE in vitro. Partial physicochemical characterization of this factor has shown that it is heat labile, has an m.w. between 10,000 and 30,000 M(r), and is a mannose-rich glycoprotein.

Brugia pahangi: serum-dependent cell-mediated reactions to sheathed and exsheathed microfilariae

The immune mechanisms operating on the sheath and the cuticle of the Brugia pahangi microfilariae have been studied in vitro. The intact and exsheathed parasites were used for this purpose with serum from albino rats immunized with sonicated homogenates of the parasites as the source of antibodies. The IgG component of the serum was found to promote adherence of rat leucocytes and death of the sheathed and exsheathed parasites in presence of fresh normal serum. EDTA and EGTA abolished the adherence activity suggesting the involvement of complement components via the classical pathway. Both macrophages and neutrophils participate in this reaction. Eosinophils exhibit marginal activity only on exsheathed parasites. The intensity of adherence and killing by neutrophils in the presence of immune serum was greater with the exsheathed microfilariae than with the sheathed ones.

Immunity to Brugia pahangi in athymic nude and normal mice: eosinophilia, antibody and hypersensitivity responses

Congenitally athymic nude (nu/nu) mice, immunologically reconstituted by thymus grafting before inoculation with infective larvae, and mice heterozygous for the nu gene (nu/+), mounted potent protective humoral and cellular immune responses to Brugia pahangi. Although responses were not identical, both groups of mice produced IgM, IgG and IgE antibodies specific for adult worm antigen (S-Ag) present in a crude aqueous extract, made immediate and delayed hypersensitivity footpad swelling responses when challenged with S-Ag and eliminated their infection in the early larval stages. Heterozygotes also exhibited a marked eosinophilia which peaked coincident with larval killing. In contrast, thymus grafting of patent nudes had no effect upon microfilaraemias or adult worm burdens and did not completely protect against a challenge larval inoculum although antibodies specific for S-Ag were produced. With the occasional exceptions of moderate immediate footpad swelling and very low titres of IgM specific for S-Ag, no specific immune responses to B. pahangi were found in ungrafted nude mice which allowed full development of adult worms and supported patent infections.

Immunoradiometric assay for detection of filarial antigens in human serum

The immunoradiometric assay (IRMA) for detection of filarial antigens in the serum of patients infected with Brugia malayi (Bm) or the closely related filarial parasite Wuchereria bancrofti (Wb) was investigated, and its performance and clinical utility were examined. Reference sera prepared by the addition of crude Bm antigen (BmA) to negative control human sera provided a reproducible reference curve. The IRMA displayed acceptable precision and reproducibility. Agreement between dilutions (parallelism) was good in sera without specific antibody, but the presence of even modest levels of antibody resulted in nonparallelism in about one-half of the tested sera from endemic areas. Significant reduction in detectable BmA occurred when low levels of specific antibody (less than 1 microgram/ml) were added to BmA containing sera. Thus, antibody interference limited absolute quantitation of antigen in the IRMA. Results were therefore expressed in a semi-quantitative manner by using the mean + 3 SD of the binding of nonexposed human sera as the positive threshold. The frequency of reliable filarial antigen detection in individuals from the Wb endemic areas of India and the South Pacific was the following: microfilaremia, 15 out of 15; elephantiasis, 2 out of 18; tropical pulmonary eosinophilia, 2 out 8. These findings show clearly that a two-site IRMA can effectively detect circulating antigen (and thus be diagnostic of infection) in a great many patients with filariasis, but to enhance the sensitivity of the assay to the point where all patients can be diagnosed, a number of suggested modifications will be necessary.

Induction of host resistance to Brugia pahangi in jirds (Meriones unguiculatus) protected by chemoprophylaxis

Jirds were given a chemoprophylactic inoculation of flubendazole (FMBZ) and then five injections of infective larvae of Brugia pahangi whilst still protected by the FMBZ. When the drug was thought to be non-effective the jirds (and controls) were given a challenge infection of B. pahangi larvae. By comparison with control jirds the treated-infected-challenged jirds had 40% fewer adult worms. The control treated-challenged jirds contained mostly sterile female worms showing that they were still partially protected by FMBZ but worms numbers were not significantly reduced as compared with untreated controls.

Effect of diethylcarbamazine on serum-dependent cell-mediated immune reactions to microfilariae in vitro

The effect of diethylcarbamazine citrate (DEC) on serum-dependent cellular adherence and cytotoxicity to sheathed and exsheathed microfilariae of Litomosoides carinii and Brugia pahangi in vitro has been investigated. DEC at 5 micrograms/ml promoted antibody-mediated neutrophil adherence and cytotoxicity with sheathed L. carinii microfilariae. With exsheathed parasites, the drug promoted significantly complement-and antibody-mediated cellular adherence and cytotoxicity. In the case of B. pahangi, antibody-dependent cell-mediated cytotoxicity (ADCC) of neutrophils to sheathed and exsheathed microfilariae were similarly stimulated by DEC. Pre-incubation of microfilariae with DEC promoted the cellular adherence and cytotoxicity whereas pre-incubation of cells had no such effect. DEC stimulated the adherence of eosinophils to both sheathed and exsheathed microfilariae of the two species but the adherence resulted in cytotoxic effect only on the L. carinii microfilariae. DEC at higher concentrations (100 or 500 micrograms/ml) inhibits these processes. Data on the role of different serum factors involved in this phenomenon have been presented and discussed.

Immunoglobulin interactions with surfaces of sheathed and unsheathed microfilariae

The sheath surface of Brugia pahangi microfilariae (mf) and the cuticle surface of Dirofilaria immitis mf were compared with regard to the ultrastructural arrangement of neutral and charged polysaccharides and binding of immunoglobulins from dog sera. Brugia pahangi: mf demonstrated large amounts of neutral sugar and negatively charged sugars just above the sheath surface, projecting some distance from the surface, in addition to a dense layer of sulphated material on the sheath surface. Microfilariae from high microfilaremic dogs showed no innately bound IgG or IgM when examined fresh from serum nor did they bind IgG or IgM from normal (NDS) or infected (IDS) dog sera after 48 h maintenance in RPMI 1640. Many of these mf did bind IgG and IgM from hyperimmune dog serum (ImDS) and these immunoglobulins were found binding at a distance from the sheath similar to that of the sugars. Dirofilaria immitis mf demonstrated much less neutral sugar at the cuticle surface, no negatively charged sugars and a diffuse, rather than dense, distribution of sulfated material extending from the cuticle. The majority of these mf showed innately bound IgG and IgM. After 48 h maintenance in RPMI 1640 D. immitis mf bound and shed IgG and IgM from NDS, high microfilaremia D. immitis IDS and D. immitis mf ImDS at distinctly different rates.

Vaccination of BALB/c mice against Brugia malayi and B. pahangi with larvae attenuated by gamma irradiation

The vaccination with radiation-attenuated infective larvae of Brugia malayi and B. pahangi was attempted and evaluated in BALB/c mice. Two weeks after intraperitoneal infection with 100 3rd stage larvae, the worms of both species of Brugia were recovered in the peritoneal cavity of BALB/c mice. The average recovery was more than 20% in both Brugia infections. Groups of 10 mice were vaccinated subsequently three times with 100 3rd stage larvae of B. malayi or B. pahangi attenuated by 20 krad gamma irradiation and challenged with the homologous species. Vaccinated mice showed a 95.5% reduction in recovered worms in the challenge infection with B. malayi as compared to the infection in non-vaccinated controls, and a 93.8% reduction in the B. pahangi group.

The presence of blocking factors in Brugia malayi microfilaraemic patients

Serum from microfilaraemic patients have been shown to be unable to promote the antibody-dependent, cell-mediated adherence reaction to infective larvae of Brugia malayi in vitro. In this study, it was found that peripheral leucocytes from microfilaraemic patients were also incapable of promoting the adherence reaction even when incubated with serum of tropical pulmonary eosinophilia (TPE) patients. The TPE sera would normally promote the most intense adherence reaction. It was further shown that preincubation of normal human peripheral leucocytes with sera of microfilaraemic patients would similarly render them incapable of adherence. Such preliminary studies suggest that blocking factors may be present in microfilaraemic patients.

Stage-specific and common antigens of Brugia malayi identified with monoclonal antibodies

To identify parasite antigens that trigger protective, pathogenic, and allergic immune responses during filarial infections, we generated a series of monoclonal antibodies to infective larvae, adult worms, and microfilariae of Brugia malayi, a human pathogen. Quantitative and qualitative analysis of the reaction patterns of these monoclonal antibodies indicates the existence of stage-specific antigens of B. malayi, as well as of antigens shared by different stages of this parasite and by other related and unrelated helminths. These antibodies should provide invaluable tools for the analysis of host-parasite interactions in filariasis at the molecular level.

Excretory-secretory and somatic antigens in the diagnosis of human filariasis

In order to compare the immunodiagnostic value of excretory-secretory (E-S) antigens derived from adult Brugia malayi worms with somatic antigens derived from adults, microfilariae (Mf) and infective larvae (L3) of these parasites, well defined serum pools from patients with filarial (brugia, bancrofti, loa and perstans) and non-filarial (ascaris, stronglyoides, toxocara, echinococcus, cysticercus and schistosoma) helminth infections were tested against antigens derived from these different life cycle stages of B. malayi in a Staphylococcus aureus radioimmunoprecipitation assay (S. aureus RIA). The adult brugia antigens proved significantly more discriminatory than those of the other parasite stages, with the homologous brugia serum pool also showing greater reactivity to adult than to L3 and Mf antigens. Similar results were obtained when individual sera from patients (rather than serum pools) were tested in the same assay. The most surprising finding was the minimal reactivity seen between the adult filarial antigens and the non-filarial serum pools despite the presence in these pools of strong antibody reactivity with their homologous antigens. The reasons underlying the unexpected specificity of this S. aureus RIA for discriminating among sera from filarial and non-filarial infections were analysed qualitatively by immunoprecipitation techniques. It was found that use of the chloramine-T method for radioiodination resulted in preferential labelling of the low molecular weight (mol. wt) proteins (10-70,000 daltons) in the B. malayi adult somatic antigen and that these antigens were bound primarily by the filarial and not the non-filarial serum pools. These findings suggest that lower mol. wt helminth antigens may show greater species specificity than those with higher mol. wt, and those with higher mol. wt, greater cross-reactivity. If substantiated by further analysis, such results would have important implications for the subsequent isolation of diagnostically important filarial parasite antigens.

Studies on filariasis in Singapore: immunodiagnosis using indirect immunofluorescence

Filarial antibodies were detected by the indirect fluorescent antibody (IFA) technique using sonicated microfilariae of Brugia malayi as antigen. Of the 324 sera of patients with clinical symptoms suggestive of filarial infection, 90 (28%) had detectable antibodies with titres ranging from 1 : 4 to 1 : 4096. Forty-six percent of patients with eosinophilic lung were positive with titres ranging from 1 : 4 to 1 : 1024. Highest rates of positives were seen in Indians (48%) with lower rates in Malays (36%) and Chinese (15%).

Comparison of heterologous adult Brugia malayi and homologous Onchocerca volvulus antigen in the enzyme-linked immunosorbent assay (ELISA) for Guatemalan onchocerciasis

To determine the susceptibility of a heterologous filarial antigen for measuring Onchocerca volvulus antibodies, worms were compared using an enzyme-linked immunosorbent assay (ELISA) test. Control serum samples from helminth-free U.S. residents and from helminth-infected but filariae-free Salvadoran residents were tested and compared with serum obtained from microfilariae-positive and -negative Guatemalan residents living in an area of endemic onchocerciasis. The results showed that none of the sera from U.S. residents had positive O. volvulus ELISA titers (greater than or equal to 1:160); however, 8.51% (4/47) had positive B. malayi ELISA titers (greater than or equal to 1:640). The geometric mean titers with the B. malayi ELISA test were higher than with the O. volvulus ELISA test--in sera from 47 U.S. residents (1:219 vs. 1:49), from 108 Salvadoran residents (1:92 vs. 1:71), and from 145 microfilariae-negative (1:539 vs. 1:167) and 303 microfilariae-positive (1:1,270 vs. 1:561) Guatemalan residents. The B. malayi ELISA test exhibited slightly less sensitivity than the homologous O. volvulus ELISA test; nevertheless, a good correlation (r = 0.74) was found between the 2 test antigens, indicating that the B. malayi antigen could be used to measure O. volvulus antibodies.

Immunoregulation in experimental filariasis. IV. Induction of non-specific suppression following in vitro exposure of spleen cells from infected jirds to Brugia pahangi antigen

Studies with inbred jirds chronically infected (greater than 5 months) with Brugia pahangi have demonstrated splenic suppressor cells which modulate in vitro responsiveness to mitogens and parasite antigens. The stimuli which induce suppression were characterized by analysing the effect of activated cells from inbred normal or B. pahangi-infected jirds on the PHA and PWM responsiveness of cultures on normal cells. Regulatory cells were stimulated in vitro with concanavalin A (Con A; 5 micrograms/ml) or an extract of adult B. pahangi (20 micrograms/ml) for 72 hr and irradiated (1500 rads) prior to cocultivation with normal cells. Addition of Con A-activated normal spleen cells to normal cells produced moderate suppression of PHA and enhancement of PWM responsiveness. However, Con A-stimulated spleen cells from infected animals consistently suppressed both the PHA and PWM responsiveness of normal cells by 80-90%. Spleen cells from chronically infected jirds were also induced by B. pahangi antigen to suppress both the PHA and PWM responsiveness of normal lymphocytes. In contrast, spleen cells from animals 3-15 weeks after infection and lymph node cells from all time points were capable of suppressing only PWM responses when stimulated by antigen. Normal spleen cells were not induced by B. pahangi antigens to exhibit immunoregulatory activity. The suppression mediated by antigen-induced spleen cells from chronically infected jirds was partially or totally alleviated by removal of non-specific suppressor cells which are plastic adherent and cyclophosphamide-sensitive, or by removal of antigen-specific suppressor cells which bear receptors for histamine. the results suggest the involvement of regulatory cell circuits in experimental filarial infections.

Immunoregulation in experimental filariasis. III. Demonstration and characterization of antigen-specific suppressor cells in the spleen of Brugia pahangi-infected jirds

Antigen specific immunoregulatory phenomena in both human and experimental filariasis are correlated with the presence of circulating microfilariae. Previous studies of inbred jirds infected with Brugia pahangi have demonstrated that the onset of microfilaremia (8-10 weeks post-infection) is associated with a loss of responsiveness to parasite antigens in the spleen, but not the lymph nodes of infected animals. The present experiments defined immunoregulatory phenomena responsible for altered antigen-specific in vitro lymphocyte blastogenesis in the spleen of B. pahangi-infected jirds. Diminished splenic responsiveness to B. pahangi antigens was associated with the presence of a cell capable of suppressing the responsiveness of lymph node cells from infected jirds to parasite antigens. antigen-induced in vitro blastogenic responsiveness of spleen cells from microfilaremic , but not normal animals was restored by depletion of cells adherent to nylon wool or bearing receptors for histamine, peanut agglutinin, soybean agglutinin or jird Fc. The responsiveness of spleen cells from chronically infected (greater than or equal to 20 weeks) animals to mitogens, but not parasite antigens, was enhanced by removal of plastic-adherent cells. The results suggest the involvement of antigen-specific suppressor T cells, in the spleen of B. phangi -infected jirds which are distinct from non-specific suppressor cells previously described in this system.

A monoclonal antibody to surface antigens on microfilariae of Brugia malayi reduces microfilaremia in infected jirds

A monoclonal antibody to surface antigens of Brugia malayi microfilariae promotes the adherence of peripheral blood cells to microfilariae in vitro and reduces microfilaremia in vivo. The antibody reacts with epitopes present on two stage-specific antigens with estimated molecular weights of 70,000 and 75,000 daltons.

Limitations of the radioimmunoprecipitation polyethylene glycol assay (RIPEGA) for detection of filarial antigens in serum

The performance of the radioimmunoprecipitation polyethylene glycol assay (RIPEGA) was examined for quantitation of filarial antigens (Brugia malayi and Dirofilaria immitis) in serum from infected human and animal hosts and non-infected controls. Multiple PEG concentrations were employed to determine the level of non-specific binding (NSB) in non-exposed human sera (NEHS) containing no filarial antigen. The NSB observed when 3 different 125I-labeled IgG antibodies were added to 26 NEHS varied 3-fold and was correlated significantly with total serum IgM (r = 0.80, P less than 0.005, n = 24) but not with serum IgA (r = 0.37) or IgG (r = 0.45). NSB levels were significantly reduced when a Fab'2 fragment of the 125I-labeled antibody was used, but the correlation of NSB with total serum IgM remained significant (r = 0.57, P less than 0.01). The presence of rheumatoid factor in NEHS sera also significantly increased NSB by an average of 3-fold. These effects eliminated the assay's ability to detect in sera from infected hosts filarial antigen the presence of which could be readily demonstrated by an immunoradiometric assay. The RIPEGA's precision (intra-assay coefficient of variation (CV) = 21% at 35% Bmax) and reproducibility (inter-assay CV = 29% at 35% Bmax) are less satisfactory than many alternative immunoassays. In many cases, positive sera failed to dilute out in parallel with each other or with an antigen-spiked standard reference curve. We conclude that poor performance characteristics currently limit the utility of the RIPEGA for quantitating filarial antigen in human and animal serum.

Different suitability of 3 filarial antigens (Litomosoides carinii, Dipetalonema viteae, Dirofilaria immitis) to act as allergens in the Passive Cutaneous Anaphylaxis Test and to serve as antigens in an ELISA in the course of experimental filarial infections (L. carinii, D. viteae, Brugia malayi, B. pahangi) of Mastomys natalensis

Crude extracts of adult worms of 3 different filariae (Litomosoides carinii, Dipetalonema viteae, Dirofilaria immitis) were evaluated for their suitability to serve as allergens in the Passive Cutaneous Anaphylaxis Test (PCA) and as antigens in an ELISA which detected mainly IgG antibodies. Studies were done in the course of 4 different filarial infections (L. carinii, D. viteae, Brugia malayi, B. pahangi) of Mastomys natalensis, using sera from different times after infection up to 350 days p.i.--In the PCA L. carinii and D. viteae antigens, apart from L. carinii infection caused reactions to a similar degree. In the L. carinii infection the homologous antigen was more effective. The D. immitis antigen was clearly less effective: high titres were found only during the early prepatency of D. viteae and Brugia infections and during the early patency of L. carinii and D. viteae infections. In all other cases, if at all, it led to weak reactions only.--In the ELISA different time courses were obtained as well. In Brugia infections values obtained with D. viteae and D. immitis antigens were significantly correlated but were not related to those obtained by the L. carinii antigen. However, the L. carinii antigen detected high levels of antibodies especially during prepatency of B. malayi, B. pahangi and D. viteae infections. No relations were found between the antigens for the D. viteae infection. In the case of the L. carinii infection the values of all 3 antigens were significantly correlated.

Increased activity of macrophages from mice infected with Brugia pahangi: in vitro adherence to microfilariae

After the inoculation of infective larvae of Brugia pahangi into the peritoneal cavities of CBA/Ca mice adult worms developed, but by 12 weeks post-infection the parasites were usually dead and surrounded by granulomatous tissue. Macrophages were the most common cell type in these granulomas and were also found in increasing numbers free in the peritoneal cavity. We have investigated the ability of macrophages to damage microfilariae in vitro, in a system where microfilariae were cultured together with cells and serum taken from either uninfected female CBA/Ca mice or at various intervals after infection. Macrophages adhered to and killed microfilariae in this system and there was an increase in vitro adherence of these cells during the course of infection. The peak level of in vitro activity of these cells coincided with the phase of parasite killing in vivo. The presence of serum also affected the degree of macrophage adherence and subsequent death of the parasite. Analysis of serum components using EGTA, zymosan or heat inactivation suggested that complement and possibly heat labile antibody were involved. Immunoglobulins were shown by immunofluorescence to be present on the surface of microfilariae cultured in serum from infected mice. It is concluded from this study that macrophages are actively involved in the termination of murine filarisis.

Serosuppression in experimental filariasis

Both antigen specific and non-specific immunoregulation by cells have been described in jirds infected with Brugia pahangi, but the contribution of serum factors to immunoregulatory phenomena in this infection has not been examined. The present study determined the effect of serum from normal or B. pahangi infected jirds on the mitogen responsiveness of spleen cells from uninfected animals and on the antigen responsiveness of lymph node cells (LNC) from infected jirds. Addition of heat-inactivated jird serum to cultures of cells supplemented with 1% fetal bovine serum demonstrated that serum from chronically infected (greater than or equal to 20 weeks post-infection), but not normal jirds consistently suppressed responsiveness of LNC from infected jirds to B. pahangi extracts in a dose-dependent manner (0.25%-1% concentration). A comparison of sera from jirds at different times post-infection demonstrated that sera (1%) from chronically infected (30 weeks; 100% suppression), but not acutely infected (4 weeks; 0% suppression) or recently microfilaremic (10 weeks; 11% suppression) animals were capable of suppressing antigen reactivity of LNC. In contrast, the inhibitory effect of serum on lymphocyte reactivity to the mitogens, PHA and PWM, was observed intermittently throughout the course of the infection and was less than the effect of chronic serum on antigen responsiveness. The B. pahangi antigen response of spleen cells from infected jirds depleted of suppressor cells by fractionation over nylon wool was also inhibited by chronic sera. Following fractionation of chronic sera by Sephadex G-200 chromatography, suppressor activity was observed in the void volume and IgG peaks. Suppressor activity was not associated with protein A, anti-jird Ig, or B. pahangi antigen bound fractions, nor with polyethylene glycol precipitable material.

Activation of jird (Meriones unguiculatus) macrophages by the filarial parasite Brugia pahangi

Peritoneal macrophages from Mongolian jirds (Meriones unguiculatus) with either lymphatic or intraperitoneal infections of Brugia pahangi were studied to determine the effects of infection on macrophage function and morphology. Macrophages were collected at 40, 90, 140, and 200 days after inoculation of infective third-stage larvae and assayed for phagocytic and bactericidal activity by the acridine orange method and for morphological changes by light and electron microscopy. Significant increases in phagocytic and microbicidal activity (P less than or equal to 0.01) were observed in peritoneal macrophages collected from jirds with intraperitoneal infections when compared with peritoneal macrophages from jirds with lymphatic infections and resident peritoneal macrophages from normal, noninfected jirds. Morphological changes in peritoneal macrophages from jirds with intraperitoneal infections were similar to those found in thioglycolate-elicited macrophage populations. Granuloma formation was also observed in the peritoneal cavities of intraperitoneally infected jirds. The peritoneal cavity may serve as a model to study cell-worm interactions in filarial nematode infections.

Brugia pahangi: antibodies and microfilaremias in Lewis rats

Male and female Lewis rats were inoculated subcutaneously in the left groin with 75 infective larvae of Brugia pahangi and microfilaremias were followed for as long as 420 days postinoculation. Patent infections developed in 64% of the female rats and 95% of the male rats. Mean prepatent periods were similar (65.9 and 63.9 days, respectively), but mean microfilaremias in males rose much higher, to a mean of 218 mf/0.25 ml blood at 270 days postinoculation. IgG titers, as measured by enzyme-linked immunosorbent assay (ELISA), to adult worm somatic antigen were higher than those to microfilariae in almost all rats. For both sexes, the most consistently microfilaremia rats had highest titers to these antigens. Granulomas with degenerating microfilaria were present in the spleen of male rats with high microfilaremias (greater than 100-300 mf/0.25 ml blood). Ouchterlony precipitin reactions suggested that most rats with spleen granulomas responded to microfilarial antigen components to which most rats without granulomas did not. Neither spleen granulomas nor antibody responses measured in this study appeared to have protective (microfi8laremia-lowering) value. As measured by microfilaremias, the male Lewis rat is not as susceptible as some conventional hosts of B. pahangi, but it does consistently become infected and remains microfilaremic for more than a year. Preferential male susceptibility indicates that this model may be useful for studying this aspect of human lymphatic filariasis.