Diagnostic use of polyclonal antibodies raised in mouse ascitic fluid in bancroftian filariasis

Polyclonal antibodies were produced against Brugia malayi adult antigens (BmA (PBS) SAg and BmA (SDS) SAg) in mouse ascitic fluid by immunising Balb/c mice intraperitoneally with high ratio of adjuvant to immunogen. The diagnostic use of these antibodies in detecting circulating filarial antigen in bancroftian filariasis was studied by sandwich enzyme-linked immunosorbent assay (sandwich ELISA) using stick assay system. Both antibodies raised against PBS and SDS soluble antigens were found to be equally sensitive and relatively specific in detection of circulating filarial antigen. When anti BmA (PBS) SAg antibody was used in sandwich ELISA, 90% of microfilaraemic sera, 30-40% of acute and sub acute filarial sera, 20% of chronic filarial sera, 7% of endemic normal sera and none of 15 non-endemic normal sera were positive for filarial antigen. Using anti BmA (SDS) Sag antibody, 93% of microfilarial sera, 40% of acute and sub acute filarial sera, 20% of chronic filarial sera and none of 15 endemic and non-endemic normal sera showed the presence of filarial antigen. The filarial antigen detection using anti BmA S Ag antibodies produced in mouse ascitic fluid in sandwich ELISA may be useful in detection of active stage (microfilaraemia) of infection.

Non-specific immune suppression by CD8+ T cells in Brugia pahangi-infected rats

Non-specific suppression of the immune response was investigated in Brugia pahangi-infected Lewis rats. The proliferative response of peripheral blood lymphocytes or splenic non-adherent cells to mitogens was significantly reduced by B. pahangi infection. The degree of hyporesponsiveness of splenic non-adherent cells to mitogens was comparable between microfilaremic and non-microfilaremic animals. The suppressed proliferative response of splenic non-adherent cells was restored by blocking with anti-CD8 monoclonal antibody. After separation of T cells into CD4+ and CD8+ subpopulations, only CD8+ T cells from B. pahangi-infected rats suppressed the proliferative response of normal spleen cells to concanavalin A. CD8+ T cells from normal rats had no suppressive effect. On the other hand, the proliferative response of CD4+ T cells to concanavalin A was comparable between normal and infected rats. These results suggest that CD8+ T cells participate in the non-specific suppression of immune response in experimental filariasis.

Parasite antigenemia in untreated and treated lymphatic filarial infections

To evaluate the merit of antigen detection assays as a tool to monitor the efficacy of chemotherapy for lymphatic filariasis, we serially measured antigen levels in sera from jirds infected with Brugia malayi and from humans with bancroftian filariasis. Antigenemia was detected in all animals with parasitologically proven infection and was present in jirds with prepatent or occult filariasis. Antigen levels correlated with worm burdens, and progressively declined in drug-cured animals. Treatment with diethylcarbamazine (DEC) triggered a transient increase in serum levels of filarial antigens bearing the epitope recognized by the monoclonal antibody HC 11. All patients with bancroftian filariasis became amicrofilaremic within one week after DEC treatment. Antigenemia levels slowly declined over a period of several months in all but one treated individual. Forty-two months after treatment, progressively rising antigen levels are present in 10 patients. Six of these remain amicrofilaremic; in the other 4, elevated antigenemia levels preceded or were detected at the same time as recurrent parasitemia. Periodic monitoring of antigenemia levels after treatment of patients with lymphatic filariasis can be used to identify individuals who are likely to develop recurrent microfilaremia before the parasites become detectable in blood samples, thereby allowing timely retreatment.

Brugia pahangi: effects of duration of infection and parasite burden on lymphatic lesion severity, granulomatous hypersensitivity, and immune responses in jirds (Meriones unguiculatus)

The effects of Brugia pahangi infection duration and parasite burden on parasite-associated inflammatory and immune responses were determined over a 181-day period in jirds receiving from one to eight inoculations of infective larvae. Multiple infections did not produce a protective resistance to reinfection as determined by adult worm recovery at necropsy. Intralymphatic granulomatous lesions, lymph thrombi, were first seen at 48 days post initial inoculation (DPI). The numbers of lymph thrombi reached peak levels in singly inoculated jirds at 90 DPI and significantly decreased to low levels by 160 DPI. The ratio of lymph thrombi to adult worms recovered from the spermatic cord lymphatics followed a similar pattern. Sizes of renal lymph nodes, which drain lymphatics containing parasites, followed a temporal pattern of increase and decrease similar to that of lymph thrombi numbers. Peak granuloma areas around antigen-coated beads embolized in lungs were seen at 27 DPI. Granuloma areas around antigen-coated beads began to decrease after 69 DPI and reached sizes not significantly different from uninfected controls by 118 DPI. Multiple inoculations of infective larvae and increasing worm burdens did not affect the pattern of granulomatous response to antigen-coated beads. Eosinophilia of singly and multiply infected jirds peaked at 26 DPI. Eosinophilia of singly infected jirds returned to normal levels by 103 DPI but those of multiply infected jirds remained elevated until 160 DPI. Lymph node cell blastogenic responses to antigen were greater than those of splenocytes at all time intervals measured. However, significant differences in stimulation indexes between groups with different infection durations were not seen with either cell type. Antibody responses to somatic adult worm antigen as measured by ELISA reached near peak levels by 48 DPI and remained elevated for the course of the study in all infected jirds. The decrease in lymphatic lesion severity seen in chronically infected jirds temporally corresponds to the decrease in granulomatous reactivity measured around antigen-coated beads embolized in the lungs. This observation suggests that host and/or parasite factors associated with these two phenomena may be similar. Although these decreases may be the result of down-regulated immune responses, corresponding decreases in antibody levels and blastogenesis of lymphocytes stimulated by crude worm extracts were not observed in chronic infections.

Antibody-mediated cytotoxic effects in vitro and in vivo of rat cells on infective larvae of Brugia malayi

Albino rat macrophages and neutrophils in the presence of immune serum adhered to and promoted killing of Brugia malayi infective larvae in vitro. At a similar cell-target ratio, macrophages were more potent than neutrophils in inducing cytotoxic response to the larvae. Eosinophils were also effective in killing but only at a high cell-target ratio. The activity in the immune serum could be absorbed to and eluted from a Protein A-Sepharose column suggesting involvement of IgG antibody in the reaction. An indirect fluorescent antibody test confirmed the presence of IgG on the surface of larvae incubated in immune serum. Infective larvae were attacked by host cells within micropore chambers 16-24 h after implantation into immunized rats. Further, a strong cytotoxic response to the larvae was seen when they were introduced intraperitoneally into immune rats indicating the role of antibody and cells in vivo. We suggest that antibody-dependent cellular cytotoxicity may represent an important mechanism of parasite killing in an immune host.

MHC and non-MHC-restricted recognition of filarial surface antigens in mice transplanted with adult Brugia malayi parasites

We describe here the genetic control of humoral responses to filarial nematode Ag elicited by live adult Brugia malayi parasites in mice. Inbred and congenic mice of two different MHC haplotypes, H-2k and H-2d, were examined. Serologic analysis showed that the humoral responses to the major surface 29-kDa glycoprotein of adult parasites and a 40-kDa Ag from the surface of the microfilarial stage were restricted to mice with H-2k alleles (B10.BR, CBA/Ca, and CBA/N), whereas mice of the H-2d haplotype (B10.D2/n and BALB/c) were nonresponsive to these Ag. Conversely, internal adult Ag of molecular mass of 24 and 66 kDa were recognized only by animals with the H-2d haplotype. Apart from MHC-restricted recognition, the level of responses to phosphorylcholine and to a 15-kDa adult surface molecule were found to be influenced by non-MHC genes. A sharp restriction was also observed to an adult surface Ag complex of 17 to 200 kDa, which was recognized only by BALB/c mice. Thus, multiple examples of both H-2 and background genetic effects on the immune response to distinct filarial Ag can be found.

A comparison of host responses of the Mongolian jird to infections of Brugia malayi and B. pahangi

Host responses of jirds receiving a single subcutaneous inoculation of subperiodic Brugia malayi were compared with those of jirds similarly infected with B. pahangi. Parasite burdens, lymphatic lesion severity, granulomatous reactivity, antibody responses to parasite antigens, and complete blood cell counts were assessed at 60 and 150 days post-inoculation. At 60 days post-inoculation, percentages of adults recovered at necropsy and lymphatic lesion severity were greater in B. pahangi-infected jirds. At 150 days post-inoculation, lesion severity and percentages of worms recovered were similar in both infections. No significant differences were noted in either infection in reactivity to homologous or heterologous parasite antigens in any parameter measured. Similarities in the kinetics of the inflammatory reactivities of the 2 infections suggest that previous observations made in the jird-B. pahangi model could be utilized in designing studies using B. malayi. Further, the more marked lesion severity observed in B. pahangi-infected jirds and the relative ease of maintaining B. pahangi in the laboratory support the continued use of this system as a conceptual model for the study of lymphatic lesion pathogenesis.

The BALB/c mouse as a model for immunological studies of microfilariae-induced pulmonary eosinophilia

Tropical pulmonary eosinophilia (TPE) is believed to result from extreme immediate hypersensitivity to microfilariae localized in the pulmonary vasculature of some persons with lymphatic filariasis. Female BALB/c mice repeatedly immunized by ip injection of Brugia malayi microfilariae become amicrofilaremic within 24 hr of iv parasite challenge, whereas non-sensitized control animals remain patent for greater than 72 hr. Immunized, but not control mice, develop peripheral blood and pulmonary eosinophilia (2,000 cells/mm3 and 65,000 cells/bronchoalveolar lavage, respectively). Serum and bronchoalveolar lavage filarial-specific IgG antibodies are greater in sensitized mice than in controls (ELISA absorbance values 20- and 10-fold higher, respectively). Serum IgE antibody levels are also greater (P less than 0.01) in immunized parasite-challenged mice than in controls (mean cpm 125I-labeled anti-mouse IgE bound to B. malayi antigen-coated Sepharose beads: 7,852 vs. 1,741, respectively). This model exhibits several of the major features of human TPE: amicrofilaremia, elevated levels of serum IgG and IgE antibodies to microfilariae, and blood and pulmonary eosinophilia. This model may be useful in the examination of the role of filarial antigen-specific lymphoid cells and antibodies in regulating the pathologic responses to microfilariae trapped in the lung.

Anti-idiotypic antibodies function as a surrogate surface epitope of Brugia malayi infective larvae

Anti-idiotypic (AB2) antibodies were generated in rabbits following immunization with a murine IgM monoclonal antibody (AB1) recognizing a surface determinant of Brugia malayi infective stage larvae. AB2 specifically inhibited the binding of AB1 to B. malayi larvae. Furthermore, AB2 had the ability to mimic the original antigen since mice immunized with AB2 possessed serum antibodies (AB3) specific for the B. malayi surface determinant. The presence of anti-surface antibodies (AB3 and AB1) induced either by AB2 immunization or by administration of AB1, did not alter the outcome of an intraperitoneal infection of B. malayi larvae in BABL/c mice when compared to untreated animals. AB3 antibodies like AB1, were IgM, thus indicating an isotype restricted response to the B. malayi epitope. There were no detectable cell mediated responses to the surface determinant in mice immunized with AB2, assessed by lymphocyte blastogenesis or IL3 production in vitro in response to the idiotope as presented by living larvae. The lack of cellular responses and/or the previously demonstrated rapid shedding of the epitope may explain the inability of AB1 or AB2 to protect mice against larval challenge in this study.

Differential humoral and cellular immunoreactivity to saline- and detergent-extracted filarial antigens

The immunoreactivity to saline- and detergent-extracted filarial antigens of 31 Haitian subjects exposed to or infected with Wuchereria bancrofti was analysed. Cellular reactivity, monitored by blastogenesis in vitro, was significantly greater to a soluble extract of Brugia pahangi than to a detergent-extracted antigenic preparation. In contrast, serum antibody levels against the detergent extract were significantly higher. These differences were consistently observed in symptomatic, microfilaraemic, and asymptomatic/amicrofilaraemic groups of patients. These patterns of immunoreactivity may reflect intrinsic differences between the 2 antigenic preparations in terms of composition or their mode of presentation to the host immune system.

In vitro killing of microfilariae of Brugia pahangi and Brugia malayi by eosinophil granule proteins

Eosinophil infiltration and degranulation around the tissue-invasive stages of several species of helminths have been observed. Release of eosinophil granule contents upon the worms is supported by localization of two of the major granule proteins, major basic protein (MBP) and eosinophil peroxidase (EPO), on and around species of trematodes, nematodes, and cestodes. In the case of filarial worms, MBP is deposited on degenerating microfilariae (mf) of Onchocerca volvulus. Here, we performed in vitro assays of the toxicity of four purified eosinophil granule proteins, namely, MBP, EPO, eosinophil cationic protein (ECP), and eosinophil-derived neurotoxin (EDN), for the mf of Brugia pahangi and Brugia malayi. MBP, ECP, and EDN killed these worms in a dose-related manner although relatively high concentrations of EDN were necessary. EPO, in the presence of a H2O2-generating system and a halide, was the most potent toxin on a molar basis; here, the most potent halide was I- followed by Br- and Cl-. Surprisingly, EPO in the absence of H2O2 killed mf at concentrations comparable to those required for MBP and ECP. The toxicity of EPO + H2O2 + halide was inhibited by heparin, catalase, or 1% BSA, whereas the toxicity of EPO alone was inhibited only by heparin. Heparin also inhibited killing by both MBP and ECP. Despite the homology of ECP with certain RNases, placental RNasin, an RNase inhibitor, was unable to inhibit ECP-mediated toxicity. These results indicate that all of the eosinophil granule proteins are toxic to mf and they support the hypothesis that eosinophil degranulation causes death of mf in vivo.

Differential recognition of Brugia malayi antigens by bancroftian filariasis sera

Individuals residing in an area endemic to Wuchereria bancrofti infection were broadly categorised as endemic normals (EN), microfilaraemics (mf + ve) and elephantoids i.e., chronic lymphatic filariasis (EL). The immune status of these three groups was examined in terms of (i) specific antibody levels; (ii) ability to induce antibody dependent cellular cytotoxicity (ADCC) to microfilariae; and (iii) ability to recognise different microfilarial antigens by immunoblotting. All three groups of endemic residents were indistinguishable in their antibody levels as measured by ELISA with B. malayi microfilarial antigen. Many endemic normal sera and most elephantoid sera exerted strong cytotoxicity against W. bancrofti microfilariae whereas none of the mf + ve sera had any such activity. Immunoblotting studies revealed that a protein with mol. wt of 79 KDa was the only one among the proteins of B. malayi microfilarial extracts that was consistently recognised by sera from all endemic residents. Endemic normal sera and elephantoid sera, which exerted maximum cytotoxicity, together specifically recognised three proteins with molecular weights 25, 58 and 68 KDa and these three proteins could be among the candidate antigens that induce resistance to filarial infection.

Differential recognition of microfilarial antigens by sera from immigrants into an area endemic for brugian filariasis

Studies in animal models indicate that antibodies to surface antigens of microfilariae participate in the control of parasitaemia resulting from infections with lymphatic filarial nematodes. In an attempt to identify parasite antigens that elicit such 'protective' host responses, we compared the antigen recognition patterns of persons who remained amicrofilaraemic after 3-6 years of exposure to Brugia malayi with those of individuals who developed patent filariasis during the same period. IgG antibodies in sera from immigrants identified between 0 and 25 microfilarial antigens on Western blots. The highest degree of reactivity was observed with antigens in the 65-75 kD and 20-30 kD ranges, and with a group of high mol. wt antigens (greater than 180 kD). Sera from amicrofilaraemic donors preferentially reacted with 70/75 kD microfilarial antigens. A proportion of such sera inhibited the binding of monoclonal antibody MF1 to its target epitope; eight of nine inhibitory sera were from patients with active infections, evidenced by the presence of microfilariae or filarial antigens in the donors' blood, but who were amicrofilaraemic. These results indicate that some amicrofilaraemic residents of areas where brugian filariasis is endemic develop immune reactions to a microfilarial stage-specific antigen that was previously identified as a potentially 'protective' parasite antigen in animal models of lymphatic filariasis.

Injection of microfilariae induces resistance to Brugia malayi infection in ferrets and accelerates development of lymphostatic disease

Ferrets injected intravenously with living microfilariae or cutaneously with microfilariae followed by intravenous injection developed partial resistance to a challenge infection as measured by recovery of adult filariae from lymphatics. Following a challenge infection, the ferrets injected with microfilariae developed lymphatic pathology characteristic of a chronic infection or that observed following multiple infections. There was disruption of lymphatic drainage of the infected limb and lymphoedema. The results suggest that immune responses to antigens of microfilariae, presumably antigens shared with other developmental stages, effected both increased resistance and enhanced lymphatic pathology.

[Determination of circulating filarial antigen using monoclonal antibody against Brugia malayi adult worm ES antigen with Dot-ELISA]

A hybridoma cell line secreting monoclonal antibody (McAb) against Brugia malayi adult worm excretory-secretory antigen (AWES) was established. The identification of the Ig sub-classes showed that McAb AWES belongs to IgG. We developed a Dot-enzyme-linked immunosorbent assay (Dot-ELISA) to detect circulating parasite antigens in human lymphatic filariasis. 75 of 77 (97.4%) bancroftian microfilaremia cases showed positive reaction. 27 out of 40 (67.5%) microfilarial patients with hydroceles, chyluria, or elephantiasis, and 20% of sera from asymptomatic residents of filariasis-endemic areas evidently contained filarial antigens. 31 of sera from non-endemic area with ascaris infection were all negative. The minimal amount of antigens in pool normal sera adding AWES antigen was detectable at 6.3 pg/ml. The results suggested that Dot-ELISA is a sensitive, specific, cheap and simple agent for use in epidemiological field studies.

Phosphocholine-containing antigens of Brugia malayi nonspecifically suppress lymphocyte function

The immunosuppressive effect of Brugia malayi antigen (BmA) on phytohemagglutinin (PHA) driven T cell proliferation was evaluated in patients with filariasis (n = 14) and compared to control individuals (n = 12). When peripheral blood lymphocytes were co-cultured with BmA and PHA, BmA markedly suppressed the T cell proliferative response to PHA in both filarial patients and control individuals in a dose-dependent manner. The suppression resulted neither from any direct toxicity of BmA nor from nonspecific absorption of the PHA mitogenic activity by BmA. The major suppressive component appears to be phosphocholine (PC), an immunodominant molecule present in abundance on filarial parasites and on circulating filarial antigen. Both purified PC as well as PC-containing antigens affinity purified from BmA were capable of suppressing the proliferative responses of co-cultured autologous lymphocytes to PHA. The suppressive activity was not abolished by mitomycin-C treatment and was greater in patients with filariasis than in normal controls, suggesting that levels of PC-containing antigens determines the magnitude of the suppressive effect of PC-antigen. Further, as induction of the suppressive activity was completely abrogated when antigen pre-treated cells were T cell-depleted, the suppressive effect appears to be mediated primarily by T cells.

Evaluation of filarial skin test with Brugia malayi larval antigen in the field

To obtain comparable and reproducible results by filaria skin test with B. malayi larval antigen, standard procedure has been evolved. Antigen protein of 2 micrograms per test, injected intracutaneously, was found optimum for positive skin reaction. The reaction ratio based on increase of wheal area by 2 times or more was found to be statistically significant for interpreting positive results. However, in larger field trials, the simpler measurement of increase of wheal diameter by 1 1/2 times or more was found to be equally reliable. Patients treated with diethylcarbamazine citrate, antihistaminics and anti-inflammatory drugs are likely to be unresponsive to filarial antigen and will yield incorrect information.

Protective immunity against Brugia malayi infective larvae in mice. II. Induction by a T cell-dependent antigen isolated by monoclonal antibody affinity chromatography and SDS-PAGE

A mAb directed against filarial worm secretory/excretory product and reactive with Brugia malayi larval worm surface was used in conjunction with preparative SDS-PAGE to isolate protective Ag from extracts of adult B. malayi. The IgM mAb OVH bound to a repeating carbohydrate epitope present in adult, infective, and fourth stage larvae and microfilariae of B. malayi, and on the surface of fourth stage larvae. Ag bearing this epitope were also present in the sera of hosts infected with a variety of helminths, including Brugia, Onchocerca, Dirofilaria, and Paragonimus. Affinity chromatography of SDS extract of adult Brugia, using mAb OVH immobilized on agarose beads, isolated several Ag that separated into multiple protein staining bands on SDS-PAGE. In comparing SDS-PAGE-fractionated Ag from the crude SDS extract with fractionated mAb OVH-isolated Ag for the ability to protect BALB/c mice from challenge with B. malayi-infective larvae, it was found that of the mAb OVH-isolated Ag only those at a molecular mass of 26 to 32 kDa were protective while the original SDS extract yielded protective Ag at the following molecular mass: greater than 200, 170 to 200, 40 to 44, 33 to 36, 23 to 28, 20 to 22, and 17 to 19 kDa. Although Ag isolated by mAb OVH were highly protective, they failed to induce high antibody levels against the immunogen or SDS extracts compared to crude SDS extract immunized mouse sera, as determined by immunoblot and ELISA. Transfer of nylon wool non-adherent T cells from BALB/c mice immunized with the 26- to 28-kDa fraction of mAb OVH-isolated Ag to naive mice just before challenge with infective larvae of B. malayi resulted in a 70% reduction in larvae recovered 14 days after challenge.

Tropical pulmonary eosinophilia: analysis of antifilarial antibody localized to the lung

Acute tropical pulmonary eosinophilia (TPE) is characterized by wheezing, pulmonary infiltrates, marked peripheral blood eosinophilia, and very high serum levels of filaria-specific antibodies. To evaluate the amount and character of the filaria-specific antibodies in the lungs in this disorder, bronchoalveolar lavage was carried out in individuals with acute TPE, in normal subjects, and in patients with elephantiasis or asthma. Striking elevations of total IgE were found in the lower respiratory tract epithelial lining fluid (ELF) of patients with TPE along with high levels of filarial-specific IgG, IgM, and IgE. When patients with acute TPE were treated with diethylcarbamazine and evaluated again 6-14 d later, there was marked reduction in ELF parasite-specific IgG and IgE, which paralleled a rapid clinical response. Immunoblot comparison of the antigen recognition patterns of ELF and serum antibodies demonstrated a general similarity in parasite antigens recognized, but the lung IgE and IgG antibodies appeared to recognize only a certain subset of the parasite antigens recognized by serum antibodies. Thus, a profound antibody response to filarial infection is found in the lungs of patients with TPE, suggesting that these filaria-specific antibodies play an important role in the pathogenesis of this disorder.

Protective immunity against Brugia malayi infective larvae in mice. I. Parameters of active and passive immunity

Protective immunity against infective larvae of Brugia malayi was studied in different strains of mice using various sources of antigens. The following strains of mice were susceptible to infective larvae development for 2 weeks after primary ip challenge: BALB/c, C3H/HeJ, C3H/NeN, C3H/HeJms, C57BL/6Jms, and DDD. In comparison to gerbils, BALB/c mice developed stronger resistance to infective larvae after immunization with irradiation attenuated larvae or with killed microfilariae (mf). However, killed mf failed to enhance resistance in C3H/HeJ mice, although C3H/HeN mice were strongly protected and C3H/HeJms mice were protected to a lesser degree by this antigen. Extracts of mf with phosphate buffered saline and sodium dodecyl sulfate both induced high levels of resistance in BALB/c mice. Transfer of resistance from BALB/c mice immunized with attenuated infective larvae to naive mice was accomplished at a high level at protection with nylon wool nonadherent spleen cells (T cells) but not with adherent cells treated with anti-Thy 1.2 serum and complement. In contrast, sera from immunized mice were much less protective.

Heightened anti-filarial immune responsiveness in a Haitian pediatric population

The immunological consequences of exposure to filarial infection were examined by cross-sectional serological studies. Serum samples from 121 pediatric patients (18 months-15 years of age) were analyzed in parallel with a panel of sera from adults residing in the same area of Haiti. Parasite antigen specific IgG and IgE levels were determined by ELISA. IgG levels in children were significantly elevated in humoral immunoreactivity to Brugia pahangi extracts compared to adults. In addition, anti-filarial IgG levels in amicrofilaremic children were significantly greater than in microfilaremic children. In contrast, IgG levels in adults were equivalent independent of microfilaremic status. Anti-filarial IgE levels in sera from both children and adults were low in comparison to that of a subject with tropical pulmonary eosinophilia and were unrelated to clinical status. No correlations were found between humoral responses and age, sex, or degree of parasitemia. Sera from amicrofilaremic children and, to a lesser extent, adults recognize more antigens, particularly those of high molecular weight (greater than 55 kDa), than sera from microfilaremic patients.

Paramyosin-enhanced clearance of Brugia malayi microfilaremia in mice

Progress in development of a vaccine against human filariasis has been hampered by lack of knowledge of the biochemical structure of specific Ag that induce protective immunity in experimental hosts. In the current study, antiserum to infective third-stage larvae of Brugia malayi was used to select potentially protective Ag shared by microfilariae (mf) and adult worms. A major Ag of 97 kDa (Bm 97) was identified by immunoblotting and isolated by electroelution. Immunization of mice with 2 micrograms electroeluted Bm 97 induced partial resistance to subsequent i.v. challenge with live B. malayi mf (40 to 60% reduction in parasitemia compared to controls, p less than 0.05). Immunoblot studies of B. malayi mf and adult worm lysates showed reactivity of a 97-kDa molecule with monospecific antiserum to Schistosoma mansoni paramyosin. In addition, mouse antibody to Bm 97 reacted with a 97-kDa molecule contained in wild-type Caenorhabditis elegans but not in two mutant strains deficient for paramyosin. Subcutaneous injection of mice with paramyosin (5 micrograms twice at a 2-wk interval) purified from C. elegans or B. malayi by salt precipitation induced resistance to microfilaremia (21 to 60% lower intensities than controls, p less than 0.01). These data indicate that the invertebrate muscle protein paramyosin enhances clearance of blood-borne stages of lymphatic filariae. Examination of the ability of paramyosin to induce resistance in third-stage larvae-challenged hosts is warranted.

Secreted antigens of filarial nematodes: a survey and characterization of in vitro excreted/secreted products of adult Brugia malayi

We report here a broad analysis of the excretory/secretory (E/S) products of adult Brugia malayi, collected by in-vitro cultivation of the parasite. Culture media and conditions were optimized, and non-essential amino acids were found to be crucial for efficient protein synthesis under cell- and serum-free culture conditions. A close correlation was found between total protein secretion, phosphorylcholine-bearing antigen release and lactate production on each day of culture, indicating that E/S molecules are actively secreted. Parasites cultured in vitro take 2-3 days to adjust to the new environment, and show peak levels of secretion at days 3 and 4. The active secretion of phosphorylcholine by the parasite therefore justifies the measurement of this molecule as an indication of active infection, possibly reflecting total worm burdens. By comparing metabolically labelled E/S from male and female worms, several molecules of low mol. wt, namely 10,000, 13,000, 14,000 and 22,000, together with high mol. wt components of above 12,000 were found to be female specific. Tracing the origin of the E/S products, several molecules were also found to be associated with the surface. Among these, there are at least two glycoproteins, 29,000 and 51,000 of which the 29,000 molecule is a major surface protein. The immunogenicity of the E/S was examined and antigenic cross-reactivity was found with sera from most filarial infections but not with non-filarial nematodiases such as hookworm or Trichinella. However, two molecules of low mol. wt, 15,000 and 19,000, were not recognized by anti-Onchocerca sera and appeared to be potential Brugia-specific diagnostic molecules. Possible functional roles of the adult E/S products were examined but we could find no evidence of protease activity in the E/S or glutathione S-transferase activity in either the E/S or in whole somatic extract.