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.

Prominence of IgG4 in the IgG antibody response to human filariasis

The four subclasses of IgG are distinct in structure, function, and degree of participation in the response to complex antigens. Because these differences could have important pathogenetic significance, we analyzed total and filaria antigen-specific IgG of each subclass in 31 patients with different clinical manifestations of Bancroftian filariasis. Subclass-specific, affinity-purified polyclonal antibodies were prepared from antisera raised in sheep immunized with purified myeloma IgG subclass proteins. These were radiolabeled (125I) and used to detect IgG1, IgG2, IgG3, and IgG4 in solid phase radioimmunoassays (SPRIA). The antigen-specific SPRIA was used with Brugia malayi adult antigen (BmA) bound to Sepharose 4B, whereas measurement of total IgG subclass levels in each serum was with goat anti-human IgG bound to the solid matrix. Quantification of total subclass levels was by reference to the WHO 67/97 standard, and of specific subclass antibody by development of standards from high titered sera. Although there were modest increases of total IgG1 and IgG2 in patients with filariasis compared with normals, the most striking finding was the extreme elevation of both total, and particularly, filaria antigen-specific IgG4. These elevations were seen for essentially all patients, but the relative proportion of the total IgG antibody response accounted for by IgG4 antibody was particularly marked (up to 95%) in patients with either microfilaremia or the tropical pulmonary eosinophilia syndrome. The meaning of this special prominence of the IgG4 antibody response to filarial infection is not yet clear, but the question of whether these antibodies play a role in immediate hypersensitivity reactions as either reagins or blocking antibodies is being investigated for its potential pathogenetic significance.

Prominence of IgG4 in the IgG antibody response to human filariasis

The four subclasses of IgG are distinct in structure, function, and degree of participation in the response to complex antigens. Because these differences could have important pathogenetic significance, we analyzed total and filaria antigen-specific IgG of each subclass in 31 patients with different clinical manifestations of Bancroftian filariasis. Subclass-specific, affinity-purified polyclonal antibodies were prepared from antisera raised in sheep immunized with purified myeloma IgG subclass proteins. These were radiolabeled (125I) and used to detect IgG1, IgG2, IgG3, and IgG4 in solid phase radioimmunoassays (SPRIA). The antigen-specific SPRIA was used with Brugia malayi adult antigen (BmA) bound to Sepharose 4B, whereas measurement of total IgG subclass levels in each serum was with goat anti-human IgG bound to the solid matrix. Quantification of total subclass levels was by reference to the WHO 67/97 standard, and of specific subclass antibody by development of standards from high titered sera. Although there were modest increases of total IgG1 and IgG2 in patients with filariasis compared with normals, the most striking finding was the extreme elevation of both total, and particularly, filaria antigen-specific IgG4. These elevations were seen for essentially all patients, but the relative proportion of the total IgG antibody response accounted for by IgG4 antibody was particularly marked (up to 95%) in patients with either microfilaremia or the tropical pulmonary eosinophilia syndrome. The meaning of this special prominence of the IgG4 antibody response to filarial infection is not yet clear, but the question of whether these antibodies play a role in immediate hypersensitivity reactions as either reagins or blocking antibodies is being investigated for its potential pathogenetic significance.

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.

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.

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.

IgE production in vitro by peripheral blood mononuclear cells of patients with parasitic helminth infections

Helminth parasites induce production of high levels of IgE antibodies but the immunoregulatory mechanisms determining this IgE biosynthesis are poorly understood. To investigate these mechanisms, peripheral blood mononuclear cells were obtained from six normal controls, six atopic patients and eight patients with parasitic helminth infections (three with schistosomiasis, two with loiasis, three with onchocerciasis). Cells were cultured at 1 X 10(6) cells/ml for 8 days in the presence of media alone or media supplemented with pokeweed mitogen (PWM) or cycloheximide; the supernatant fluids from these cultures were then assayed quantitatively for total and parasite specific IgE and IgG using an avidin-biotin amplified (for IgE) or standard (for IgG) microelisa assay. The geometric mean spontaneous IgE production was markedly elevated in peripheral blood mononuclear cells from parasitized individuals (2,487 pg/ml) when compared to those from atopics (358 pg/ml) or normals (152 pg/ml). Spontaneous IgG synthesis was equivalent in all three groups (range 140-420 ng/ml). PWM did not induce IgE production in any group and in the parasitized group even caused significant suppression of total IgE synthesis. Antigen specific antibody production (both IgE and IgG) paralleled total immunoglobulin synthesis. These findings demonstrate for the first time spontaneously enhanced IgE production in vitro in patients with helminth infections and provide a model system for studying the suppressive and regulatory mechanisms controlling IgE secretion.

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.

Brugia malayi: Stage-specific expression of carbohydrates containing N-acetyl-d-glucosamine on the sheathed surfaces of microfilariae

Microfilariae, infective larvae, and adult worms of Brugia malayi were incubated with a panel of seven lectins in order to study the expression of surface carbohydrates. Infective larvae and adult worms did not bind any of the lectins utilized. Microfilariae, on the other hand, bound wheat germ agglutinin. The binding of this lectin was saturable and specific, and attributed to the presence of N-acetyl-D-glucosamine. In addition, microfilariae derived in vitro bound concanavalin A, indicating the presence of glucose and/or mannose on this stage of the parasite. The fact that similar concanavalin A binding was not seen on microfilariae recovered directly from the infected host implies that there is masking or loss of parasite surface antigens as microfilariae mature in vivo.

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.

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.

Pancytopenia and hepatosplenomegaly in oxalosis

A 25-year-old woman with oxalosis and end-stage renal disease had pancytopenia and massive hepatosplenomegaly associated with extensive bone marrow deposition of calcium oxalate. A ferrokinetic study suggested profound reduction in erythrocyte production, and peripheral blood smears were compatible with myelophthisis and extramedullary hematopoiesis. Mechanical obliteration of bone marrow by calcium oxalate crystals may lead to pancytopenia and hepatosplenomegaly as late extrarenal complications of oxalosis.

IgE responses in human schistosomiasis. I. Quantitation of specific IgE by radioimmunoassay and correlation of results with skin test and basophil histamine release

We have developed a non-competitive solid-phase radioimmunoassay (SPRIA) to quantitate human IgE antibodies to Schistosoma mansoni antigens that was capable of accurately measuring IgE antibodies in both high and low titer sera. Ninety sera from "early" or "chronic" schistosomiasis patients were studied. Both levels of parasite-specific IgE antibodies and the proportion of the total IgE response that was parasite-specific were significantly lower in "early infection" sera than in sera of patients with chronic infections. The SPRIA to adult worm antigen was compared with basophil histamine release and direct intradermal skin testing also performed with the adult antigen. Both tests showed significant correlations with the SPRIA in detecting specific anti-parasite antibody.

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. IV. Analysis of the role of IgE antibodies and mast cells

Mice resistant to challenge infection with Schistosoma mansoni by vaccination with highly irradiated cercariae were examined for the presence of circulating IgE antibodies and peritoneal mast cells sensitized against schistosome antigens. Significant levels of SWAP- or CAP-specific IgE antibodies could not be detected by solid phase radioimmunoassay in the sera of C57BL/6 mice during the first 6 wk after vaccination. Similarly, heatlabile antibodies capable of passively sensitizing normal mast cells for degranulation in response to SWAP could not be identified in the same sera. In contrast, peritoneal mast cells harvested from C57BL/6 mice 2 wk or later after vaccination gave strong degranulation responses when challenged with SWAP or CAP. Thus, vaccination with irradiated cercariae induces an unusual form of immediate-type hypersensitivity in which mast cells become sensitized in the absence of detectable circulating IgE antibodies. Mice deficient in mast cells (W/Wv mutant strain) were observed to develop the same resistance to challenge infection after vaccination with irradiated cercariae as nondeficient littermates. Similarly, vaccinated SJL/J mice were found to mount an extremely weak IgE response as measured by mast cell degranulation yet displayed the same level of resistance to challenge infection as other inbred mice developing potent mast cell responses. These findings argue that IgE antibodies and mast cells are not essential components in the effector mechanism of irradiated vaccine-induced immunity against schistosome infection.

The structuring of an allergy index based on IgE-mediated skin sensitivity to common environmental allergens

We computed skin-test sensitivity levels in 485 adults puncture-tested with eight standardized, high-quality inhalant allergens tested at single concentrations. In order to quantitate the "average" IgE-mediated skin sensitivity of each subject, we used both nonparametric and parametric statistical methods to generate two "allergy indices" (Allergy Index I and Allergy Index II) based on sensitivity end-point data from the subpopulations of individuals positive to six of the eight allergens. For the 192 skin test-positive subjects, Allergy Index I and Allergy Index II were significantly correlated with each other (rs = 0.98, p less than 0.001) and with the number of positive skin-test reactions (rs congruent to 0.9, p less than 0.001) as well as with log[total serum IgE] (r congruent to 0.4, p less than 0.01). In 102 ragweed-positive subjects, log[specific IgE to ragweed] was significantly correlated with ragweed-specific "ragweed indices I and II" (r congruent to 0.6, p less than 0.01). Furthermore, the average daily symptom scores reported by 14 ragweed-positive subjects during the ragweed pollination season were significantly correlated with ragweed indices I and II (p less than 0.05). We propose the use of Allergy Index II in epidemiologic and genetic studies of allergic phenotypes as well as in clinical decisions for diagnosis and immunotherapeutic intervention.

IgE responses in human filariasis. II. Qualitative characterization of filaria-specific IgE

Crossed radioimmunoelectrophoresis (CRIE) was used to characterize human IgE antibody responses to filarial parasites by using antigens derived from Brugia malayi (Bm) adult worms. A reference pool of patient sera was initially used to determine the sensitivity and specificity of CRIE. Because IgG-blocking antibodies interfered with IgE binding in certain sera, all sera were preabsorbed with protein A-Sepharose. As little as 50 ng of specific IgE antibody (determined by quantitative radioallergosorbent test [RAST]) in the reference pool bound to 20 of the 35 antigen precipitates in crossed immunoelectrophoresis. Increasing IgE antibody concentration did not increase the number of IgE-binding precipitates. Six patients from each of the three major clinical groups in lymphatic filariasis (i.e., tropical pulmonary eosinophilia [TE], chronic lymphatic pathology [CP], or circulating microfilaremia [MF]) were studied by CRIE with the use of a constant amount of IgE antibody (50 ng IgE anti-BmA). Distinct patterns of allergen recognition were observed among the groups. Individuals with TE recognized both anodic and cathodic antigens as allergens, whereas the other two groups recognized predominantly anodic antigens. The greatest number of allergens was recognized by patients with TE; this number ranged from nine to 18, whereas patients with CP or circulating MF recognized from six to 11 allergens. Although potentiated IgE responses at a quantitative level in parasitic helminth infections is a well-established phenomenon, our studies showing the diversity of antigens recognized as allergens indicate for the first time potentiated IgE responses at a qualitative level as well.

Mechanisms of protective immunity against Schistosoma mansoni infection in mice vaccinated with irradiated cercariae. IV. Analysis of the role of IgE antibodies and mast cells

Mice resistant to challenge infection with Schistosoma mansoni by vaccination with highly irradiated cercariae were examined for the presence of circulating IgE antibodies and peritoneal mast cells sensitized against schistosome antigens. Significant levels of SWAP- or CAP-specific IgE antibodies could not be detected by solid phase radioimmunoassay in the sera of C57BL/6 mice during the first 6 wk after vaccination. Similarly, heatlabile antibodies capable of passively sensitizing normal mast cells for degranulation in response to SWAP could not be identified in the same sera. In contrast, peritoneal mast cells harvested from C57BL/6 mice 2 wk or later after vaccination gave strong degranulation responses when challenged with SWAP or CAP. Thus, vaccination with irradiated cercariae induces an unusual form of immediate-type hypersensitivity in which mast cells become sensitized in the absence of detectable circulating IgE antibodies. Mice deficient in mast cells (W/Wv mutant strain) were observed to develop the same resistance to challenge infection after vaccination with irradiated cercariae as nondeficient littermates. Similarly, vaccinated SJL/J mice were found to mount an extremely weak IgE response as measured by mast cell degranulation yet displayed the same level of resistance to challenge infection as other inbred mice developing potent mast cell responses. These findings argue that IgE antibodies and mast cells are not essential components in the effector mechanism of irradiated vaccine-induced immunity against schistosome infection.

IgE responses in human filariasis. II. Qualitative characterization of filaria-specific IgE

Crossed radioimmunoelectrophoresis (CRIE) was used to characterize human IgE antibody responses to filarial parasites by using antigens derived from Brugia malayi (Bm) adult worms. A reference pool of patient sera was initially used to determine the sensitivity and specificity of CRIE. Because IgG-blocking antibodies interfered with IgE binding in certain sera, all sera were preabsorbed with protein A-Sepharose. As little as 50 ng of specific IgE antibody (determined by quantitative radioallergosorbent test [RAST]) in the reference pool bound to 20 of the 35 antigen precipitates in crossed immunoelectrophoresis. Increasing IgE antibody concentration did not increase the number of IgE-binding precipitates. Six patients from each of the three major clinical groups in lymphatic filariasis (i.e., tropical pulmonary eosinophilia [TE], chronic lymphatic pathology [CP], or circulating microfilaremia [MF]) were studied by CRIE with the use of a constant amount of IgE antibody (50 ng IgE anti-BmA). Distinct patterns of allergen recognition were observed among the groups. Individuals with TE recognized both anodic and cathodic antigens as allergens, whereas the other two groups recognized predominantly anodic antigens. The greatest number of allergens was recognized by patients with TE; this number ranged from nine to 18, whereas patients with CP or circulating MF recognized from six to 11 allergens. Although potentiated IgE responses at a quantitative level in parasitic helminth infections is a well-established phenomenon, our studies showing the diversity of antigens recognized as allergens indicate for the first time potentiated IgE responses at a qualitative level as well.

Isolation and properties of a new short ragweed pollen allergen, Ra6

Two chromatographic forms (A and B) of the rapidly released short ragweed (Ambrosia elatior) pollen allergen Ra6 were isolated to antigenic ultrapurity by a combination of membrane filtration and ion exchange and gel filtration chromatography. Both Ra6 forms had a m.w. of 11,500 by gel filtration chromatography and 8000 by SDS-PAGE, and each consisted of two cathodically migrating bands on agarose electrophoresis at pH 8.5. Amino-terminal amino acid sequencing analysis detected two similar sequences (sequence 1 and sequence 2), which were present in different proportions in each of the chromatographic forms of Ra6. Among a ragweed-positive population sample (n = 101), 21% had specific IgE antibody (ab) and 42% specific IgG ab toward Ra6A; among ragweed-negative subjects (n = 260), 10.8% had IgG ab. We were unable to discriminate between Ra6A and Ra6B immunologically with the use of hyperimmune animal antisera or IgE and IgG ab from five Ra6-allergic humans. It appears that Ra6 is composed of at least four closely related isoallergens of similar size but slightly different charges and amino acid sequences, which appeared to be antigenically and allergenically indistinguishable according to present evidence.

Isolation and properties of a new short ragweed pollen allergen, Ra6

Two chromatographic forms (A and B) of the rapidly released short ragweed (Ambrosia elatior) pollen allergen Ra6 were isolated to antigenic ultrapurity by a combination of membrane filtration and ion exchange and gel filtration chromatography. Both Ra6 forms had a m.w. of 11,500 by gel filtration chromatography and 8000 by SDS-PAGE, and each consisted of two cathodically migrating bands on agarose electrophoresis at pH 8.5. Amino-terminal amino acid sequencing analysis detected two similar sequences (sequence 1 and sequence 2), which were present in different proportions in each of the chromatographic forms of Ra6. Among a ragweed-positive population sample (n = 101), 21% had specific IgE antibody (ab) and 42% specific IgG ab toward Ra6A; among ragweed-negative subjects (n = 260), 10.8% had IgG ab. We were unable to discriminate between Ra6A and Ra6B immunologically with the use of hyperimmune animal antisera or IgE and IgG ab from five Ra6-allergic humans. It appears that Ra6 is composed of at least four closely related isoallergens of similar size but slightly different charges and amino acid sequences, which appeared to be antigenically and allergenically indistinguishable according to present evidence.

Prenatal allergic sensitization to helminth antigens in offspring of parasite-infected mothers

Total and filaria-specific immunoglobulin E (IgE) levels were studied in cord blood from infants born in Madras, India, where filariasis and intestinal helminth infections are highly endemic. Increased total IgE levels were observed in 82% of 57 cord sera tested (geometric mean 12.6 ng/ml; range 1-1,900 ng/ml). 33 of these sera also contained IgE antibodies specific for filarial antigens as determined by solid-phase radioimmunoassay. Comparison of ratios of filaria-specific IgE to total IgE in paired maternal and cord sera suggested that cord blood IgE was derived from the fetus in most cases and not from transplacental antibody transfer. Our results suggest that prenatal allergic sensitization to helminth parasites occurs in the tropics. Such sensitization may contribute to the heterogeneity in host immune response and disease expression noted in filariasis and other helminth infections.

Endemic filariasis on a Pacific Island. II. Immunologic aspects: immunoglobulin, complement, and specific antifilarial IgG, IgM, and IgE antibodies

Sixty-eight individuals from a Pacific island hyperendemic for subperiodic bancroftian filariasis were selected from a larger study population to include the entire clinical spectrum of filarial infection in that region and also an "endemic control" group without clinical or parasitologic evidence of filarial infection. Analysis of their blood leukocyte and humoral immune responses yielded the following major findings: 1) levels of specific antifilarial antibodies of three different immunoglobulin class (IgG and IgM measured by ELISA and IgE determined by radioimmunoassay) were significantly greater in the "endemic control" population than in the patients with filariasis, an observation true for both children and adults; 2) the endemic controls also had significantly higher levels of serum IgM and C3 than did the filariasis patients 3) while individuals with "filarial fevers" and "chronic (lymphatic) pathology" did have significantly lower IgG antibody responses to filarial antigen than the controls, the lowest antibody levels were found in the patients with microfilaremia; 4) symptomatic patients (i.e., those with filarial fevers or lymphatic obstruction) regularly showed higher specific antibody responses to filarial antigens than asymptomatic, infected individuals, although the difference did not reach statistical significance. These findings are in concert with our previously reported, intriguing observation that lymphocyte proliferative responsiveness to filarial antigens was much greater in individuals of the "non-infected" endemic control population than in patients with filariasis; furthermore, they indicate the important issues that must be approached and resolved to define the immunologic determinants leading both to the various filarial clinical syndromes and to protective immunity.

Identification and characterization of excretory-secretory products of Brugia malayi, adult filarial parasites

Although E-S antigens may be particularly important for both the pathogenesis and immunodiagnosis of helminth infections, little is known about the immunochemistry or functional roles in human filarial infections. In the present paper, we have done some initial identification and characterization of E-S products of adult Brugia malayi by employing a combination of sensitive biochemical and immunochemical techniques. E-S products, collected by incubating B. malayi adults in vitro in a defined protein-free medium, were radiolabeled with 125I. SDS-polyacrylamide gel electrophoresis (PAGE) and autoradiography of labeled E-S products revealed 11 protein bands in the m.w. range of 10,000 to 70,000. Comparison of radiolabeled E-S products and adult somatic antigen (B.m.A) in SDS-PAGE indicated many common bands, and crossed immunoelectrophoresis and competitive Staph-A RIA confirmed the presence of most E-S antigens in B.m.A. Of the 11 E-S bands, two appeared to be derived from the surface of the adult worms and microfilariae as shown by SDS-PAGE and autoradiography of lodogen surface-labeled parasites; the presence of two host proteins in E-S was detected by crossed-line immunoelectrophoresis. The E-S antigens were highly immunogenic when tested both with rabbit antiserum raised against B.m.A and with a serum pool of patients with natural filarial infection.