Eosinophils and human disease

The likely roles of the eosinophil leukocyte in human disease are reviewed. The eosinophil is richly endowed with toxic cationic proteins and is able to mount a respiratory burst. Thus, eosinophils have the capability to damage various targets, and evidence exists that they do so during helminth infections and during the course of many hypersensitivity diseases. Here we discuss the role of the eosinophil in human onchocerciasis with particular attention to the Mazzotti reaction. We also discuss other diseases where eosinophil degranulation is seen, especially cutaneous diseases. Finally, the possible role(s) of the granule major basic protein in human pregnancy is noted.

Antibodies to phosphocholine-bearing antigens in lymphatic filariasis and changes following treatment with diethylcarbamazine

Sera from a total of 78 patients infected with Wuchereria bancrofti or appropriate controls were assayed for anti-phosphocholine antibodies in an enzyme-linked immunosorbent-assay (ELISA), using phosphocholine as an antigen. Anti-PC antibodies (both IgM and IgG) were observed in patients with all clinical forms of filariasis but, unexpectedly, were not significantly different from those of normal controls. Among the filariasis patients, however, individuals with patent microfilaraemia had significantly lower IgM-anti-PC titres (P less than 0.05) than did those of the other clinical groups. Competitive studies showed that 'naturally occurring' anti-PC antibodies interfere with PC antigen detection. Transient increases in the levels of circulating PC antigen were found by 3 days after treatment of microfilaraemic individuals with the filaricidal drug diethylcarbamazine. The subsequent decreases in antigen levels were generally associated with increased IgM- and IgG-anti-PC antibody levels. Such changes likely affect not only the ability to monitor the parasitological status of such individuals, but also the patient's subsequent immune interactions with filarial parasites.

Protective immunity in bancroftian filariasis. Selective recognition of a 43-kD larval stage antigen by infection-free individuals in an endemic area

There is little information about naturally occurring protective immunity in individuals living in areas endemic for lymphatic filariasis, though an immunologically hyperresponsive, uninfected group of "endemic normal" individuals that may be immune has been previously recognized. To analyze the nature of the hyperresponsiveness and its potential relation to a state of protective immunity in such individuals, strict clinical, parasitological, and serological criteria were applied to select seven "infection-free" endemic normal individuals (ENs) from a population of 459 persons resident in an area heavily endemic for bancroftian filariasis. Immunoblot analysis was used to compare the qualitative antigen recognition patterns of these endemic normal individuals to those of a group of 12 clearly infected microfilaremic individuals (MFs) from the same endemic area. Though immunoblot analysis using microfilarial and adult stage filarial antigens revealed no distinct differences in antigen recognition patterns between the two groups, when responses to infective larval stage antigens were assessed, 7/7 (100%) of the ENs were found to recognize a 43-kD antigen that was recognized by only 1/12 (8%) of the MFs. These findings are consistent with the concept that recognition of unique larval antigens may induce protective immunity to human filarial parasites and they identify a candidate immunogen for further functional assessment.

Enhanced diagnostic specificity in human filariasis by IgG4 antibody assessment

Phosphocholine (PC), an immunodominant molecule present on a wide range of organisms, including filariae, evokes antibody responses that lead to false-positive reactions in routine serological assays. Humans essentially do not respond to PC in the IgG4 subclass; therefore, by configuring an enzyme immunoassay to assess antibodies of the IgG4 subclass only, we were able to eliminate serological false-positive results in 32 of 34 cross-reactive sera from patients with non-filarial parasitic infections. Specificity was thus greatly enhanced with minimal loss of sensitivity. Because preadsorption of these cross-reactive sera to remove antibodies to PC eliminated only approximately 50% of the original cross-reactivity, other shared epitopes (perhaps similar to PC) are also likely to be restricted by IgG subclass.

Diethylcarbamazine prophylaxis for human loiasis. Results of a double-blind study

To determine whether infection with Loa loa could be prevented in temporary residents of endemic areas, we conducted a randomized, double-blind, placebo-controlled trial of diethylcarbamazine as a chemoprophylactic agent. Diethylcarbamazine (300 mg) or placebo was taken orally once a week by Peace Corps volunteers serving in Gabon, Cameroon, and the Central African Republic. The participants were assessed clinically and with serologic and parasitologic testing before and yearly during their two years of service. One hundred one persons satisfactorily completed the study. In Gabon (where exposure to the parasite was heaviest), 6 of 20 volunteers (30 percent) in the placebo group had clinical disease, as compared with none of 16 (0 percent) in the diethylcarbamazine-treated group (P less than 0.02). Of those taking placebo, 10 of 20 (50 percent) became seropositive for antifilarial IgG antibody, as compared with 2 of 16 (12 percent) in the drug-treated group (P less than 0.02). Exposure to the parasite appeared to be much lower among the 65 Peace Corps volunteers in Cameroon and the Central African Republic. No volunteer in either group in these countries had overt loiasis; 2 of 40 (5 percent) in the placebo groups in Cameroon and the Central African Republic seroconverted, as compared with none of 25 (0 percent) of those receiving diethylcarbamazine. Occasional nausea was the only symptom significantly associated with the prophylactic drug regimen. We conclude that diethylcarbamazine given orally once weekly can be an effective, acceptable chemoprophylactic agent to prevent loiasis in temporary residents of regions of Africa where Loa loa is endemic.

Eggs of Schistosoma mansoni stimulate endothelial cell proliferation in vitro

In humans chronically infected with Schistosoma mansoni, total hepatic blood flow and normal hepatic function appear to be maintained by neovascularization of the periportal fibrotic tissue. To identify possible stimuli for this neovascularization, we evaluated parasite-derived products for their ability to activate endothelial cells in vitro. Soluble egg antigen (SEA) of S. mansoni at concentrations as low as 30 ng/mL induced a marked proliferation of human umbilical vein endothelial cells (HUVE) that increased in a dose-dependent fashion; equivalent effects were seen with bovine adrenal and murine lung endothelial cells. Live, intact S. mansoni eggs secreted a soluble factor that stimulated HUVE in a manner similar to crude SEA. In contrast, adult worm extracts of S. mansoni had no significant effect on endothelial cell proliferation in any of the three cell lines tested. Preliminary biochemical characterization showed the activity to be protease sensitive and heat stable. S. mansoni SEA, in the absence of inflammatory cells, can stimulate endothelial cell proliferation in vitro.

Ivermectin for the treatment of Wuchereria bancrofti filariasis. Efficacy and adverse reactions

Ivermectin treatment was evaluated for efficacy and side effects in 40 patients in South India who had microfilaremia and bancroftian filariasis. Ivermectin was administered once orally at four dose levels (range, 25 to 200 micrograms/kg), and at each it was found to be completely effective in clearing blood microfilariae within five to 12 days. In most patients, microfilariae reappeared by three months; by six months the levels averaged 14% to 32% of pretreatment values in the four study groups, and all groups showed equivalent efficacy. Detailed monitoring identified some side effects in almost all patients: usually fever, headache, light-headedness, myalgia, sore throat, or cough that occurred most prominently 18 to 36 hours after treatment. These were most frequent and severe in patients with the greatest microfilaremia, but only when treated with the two higher doses of ivermectin (100 and 200 micrograms/kg). The low-dose (25 micrograms/kg) ivermectin group, despite equivalent efficacy in parasite killing, had clinical reaction scores that were minimal and that were not correlated with parasitemia. Since efficacy and side effects of ivermectin therapy compare favorably with those reported for treatment with the standard antifilarial drug diethylcarbamazine citrate, the major advantage of single-oral-dose administration makes ivermectin the best candidate to replace diethylcarbamazine as the treatment of choice for bancroftian filariasis.

Enhanced solubilization of immunoreactive proteins from Brugia malayi adult parasites using cetyltrimethylammonium bromide

To determine an optimal method for extracting immunoreactive proteins from filarial parasites, we have subjected Brugia malayi adult worms to a variety of solubilization regimens and compared the results. The parasites were extracted in one of seven detergents (including anionic, cationic, nonionic, and zwitterionic compounds) under varying conditions of pH, detergent concentrations, and incubation time. The individual antigen preparations were then compared both by one-dimensional SDS-PAGE and by immunoblotting analysis using a serum pool from individuals resident in an area endemic for lymphatic filariasis. The cationic detergent cetyltrimethylammonium bromide (CTAB) at 1.0% concentration, pH 7.2, consistently solubilized more proteins immunoreactive with the sera tested. Additionally, CTAB never failed to solubilize immunoreactive proteins solubilized by those other detergents or combinations of detergents studied.

Characterization of stage-specific antigens of infective larvae of the filarial parasite Brugia malayi

Three stages of the filarial parasite Brugia malayi (infective third stage larvae, adult worms, and microfilariae) were analyzed for differences in their protein composition by two-dimensional gel electrophoresis. Comparison of protein profiles of the different stages showed both identical polypeptides (reflecting common proteins) and polypeptides specific for each stage. Three polypeptides present only in infective stage larvae were seen at 72 kDa at an isoelectric point (pI) of 4.98 (p72), 30 kDa at pI 5.5 (p30), and 22 kDa at pI 4.75 (p22). p72 could be labeled chemically with 125I by either chloramine T or IODO-GEN and biosynthetically with [3H]leucine and [35S]methionine during in vitro culture of live larvae; thus, p72 is most likely a surface protein of parasite origin. The antigenic composition of these polypeptides was elucidated by immunoblot analysis. Both p72 and p22 were recognized by hyperimmune rabbit sera to infective larvae; sera from rabbits immunized with adult worms, however, did not recognize any of these Ag. Sera from humans infected with the related Wuchereria bancrofti filaria recognized only p72 and not the other two polypeptides. It therefore appears that p72 is a stage-specific but not genus-specific Ag that is immunogenic in the infected host. p22 also appears to be stage specific and, because it is not recognized by W. bancrofti-infected sera, it may be either a species-specific Ag or a poorly immunogenic molecule of the parasite. With mAb raised to p72, p30, and p22, these proteins were shown to share several antigenic determinants when analyzed by immunoblotting. The shared epitopes were present on numerous molecules with a wide range of apparent m.w. in each of the different parasite stages. Thus, despite the apparent larval stage specificity of these molecules themselves, they must contain certain epitopes shared by molecules from other stages as well. The identification of the p72 polypeptide as a molecule with epitopes exposed on the surface of infective larvae provides a candidate Ag for testing as a protective immunogen.

Characterization of stage-specific antigens of infective larvae of the filarial parasite Brugia malayi

Three stages of the filarial parasite Brugia malayi (infective third stage larvae, adult worms, and microfilariae) were analyzed for differences in their protein composition by two-dimensional gel electrophoresis. Comparison of protein profiles of the different stages showed both identical polypeptides (reflecting common proteins) and polypeptides specific for each stage. Three polypeptides present only in infective stage larvae were seen at 72 kDa at an isoelectric point (pI) of 4.98 (p72), 30 kDa at pI 5.5 (p30), and 22 kDa at pI 4.75 (p22). p72 could be labeled chemically with 125I by either chloramine T or IODO-GEN and biosynthetically with [3H]leucine and [35S]methionine during in vitro culture of live larvae; thus, p72 is most likely a surface protein of parasite origin. The antigenic composition of these polypeptides was elucidated by immunoblot analysis. Both p72 and p22 were recognized by hyperimmune rabbit sera to infective larvae; sera from rabbits immunized with adult worms, however, did not recognize any of these Ag. Sera from humans infected with the related Wuchereria bancrofti filaria recognized only p72 and not the other two polypeptides. It therefore appears that p72 is a stage-specific but not genus-specific Ag that is immunogenic in the infected host. p22 also appears to be stage specific and, because it is not recognized by W. bancrofti-infected sera, it may be either a species-specific Ag or a poorly immunogenic molecule of the parasite. With mAb raised to p72, p30, and p22, these proteins were shown to share several antigenic determinants when analyzed by immunoblotting. The shared epitopes were present on numerous molecules with a wide range of apparent m.w. in each of the different parasite stages. Thus, despite the apparent larval stage specificity of these molecules themselves, they must contain certain epitopes shared by molecules from other stages as well. The identification of the p72 polypeptide as a molecule with epitopes exposed on the surface of infective larvae provides a candidate Ag for testing as a protective immunogen.

Onchocerciasis and immunity in humans: enhanced T cell responsiveness to parasite antigen in putatively immune individuals

To identify possible immune mechanisms in human onchocerciasis, we compared a group of 12 individuals who had no clinical or parasitological evidence of infection, despite ongoing exposure to the parasite, with a group of 16 individuals from the same area who had active Onchocerca volvulus infection. Despite having less parasite-specific serum antibody, the infection-free ("putatively immune") individuals showed greater lymphocyte responsiveness, especially interleukin-2 (IL-2) production, to O. volvulus antigen (OVA) than did the infected subjects; lymphocyte responses (including IL-2 production) to mitogens and nonparasite antigen in both study groups were equivalent and normal. Our findings define differences in parasite-specific T cell subpopulations between infected and putatively immune subjects that could be a central element in developing or maintaining protective immunity to O. volvulus infection.

Immunologic correlates of the hyperresponsive syndrome of loiasis

The usual clinical picture of loiasis in long-term visitors to endemic areas differs from that in residents of these areas, with allergic symptoms, hypergammaglobulinemia, profound hypereosinophilia, and increased serum levels of IgE being more prominent. In further analyzing the immunologic correlates of this apparent hyperreactivity in 20 patients, we have found the following: (1) parasite-specific IgG (in all) and IgE (in some) were extremely elevated in the patients; (2) qualitative analysis by immunoblotting indicated multiple antigens recognized by both IgG and IgE antibodies in these patients; (3) filaria antigen-specific, lymphocyte proliferative immune responses were vigorous in all patients and, in each individual, exceed the response to other soluble antigens; (4) spontaneous and antigen-driven, parasite-specific antibody production in vitro was elevated in all six patients studied; (5) there was a significant increase in the ratio of CD4/CD8+ T cells. These observations suggest that both specific dysregulation of the immune response to the parasite antigen, as well as nonspecific immune activation, accounts for the clinically apparent hyperresponsive state seen in expatriates acquiring loiasis.

Filarial antigen in circulating immune complexes from patients with Wuchereria bancrofti filariasis

Detection of filarial antigen in circulating immune complexes from patient sera was performed by an enzyme immunoassay in which the immune complexes were precipitated in the cold with polyethylene glycol and then dissociated in an acid pH buffer before being added to an ELISA plate. The dissociated antigen bound to the plate where it could be detected by peroxidase-labeled polyclonal rabbit antifilarial antiserum. Control sera used for defining the specificity of the assay included sera with immune complexes not related to parasite infection with and without free parasite antigen added prior to polyethylene glycol precipitation as well as sera from normal individuals. Filarial antigen was detected in the circulating immune complexes from 10 of 28 patients with bancroftian filariasis residing in either the Cook Islands (subperiodic Wuchereria bancrofti) or India (periodic W. bancrofti). By immunoblotting, the most frequently identified filarial antigen in these complexes was an approximately equal to 200 kDa circulating antigen.

Parallel recognition of filarial antigens by IgE and IgG4 antibodies

IgE responses are highly modulated in human filariasis and allergic symptoms usually associated with IgE antibodies are seldom observed in individuals with Elephantiasis and Microfilaremia. Only a minor group with tropical pulmonary eosinophilia (TPE) suffer from nocturnal asthma. One possible mechanism may be the presence of IgG blocking antibodies which can block IgE mediated histamine release in vitro. Using immunoblot analysis we have further shown that remarkably similar pattern of antigen recognition were obtained with IgE and IgG antibodies which would be a major prerequisite for the blocking activity. In the present study, we have tried to determine if a particular IgG subclass is responsible for the parallelism seen with IgE antibodies. Immunoblotting with autoradiographic analysis was used to study IgE and IgG subclasses using highly characterized radiolabeled antibodies in 24 sera representing all three groups mentioned above. The most striking observation was that in 23/24 sera, the only antibody that showed consistent and parallel binding was IgG4. No consistent pattern of response was seen with any of the other three subclasses. IgG1 and 2 when present were usually directed predominantly to the high molecular weight antigens and were detected with greater frequency in Elephantiasis group. These results suggest that IgG4 may be an ideal candidate for the blocking activity seen in these sera. Such modulation of IgE responses may have important survival value for the host in filarial infection which tend to evoke rigorous IgE responses.

IgG antibody subclasses in human filariasis. Differential subclass recognition of parasite antigens correlates with different clinical manifestations of infection

The four subclasses of IgG are distinct in structure, function, and degree of participation in the antibody response to complex antigens. Looking for differential responsiveness of potential pathogenetic significance, we have analyzed both quantitatively and qualitatively the filaria-specific IgG subclass responses of 20 patients with lymphatic filariasis presenting either with chronic lymphatic obstructive pathology and elephantiasis (CP) or with asymptomatic microfilaremia (MF). Subclass-specific monoclonal antibodies were used in an enzyme-linked immunosorbent assay to study IgG filarial antibodies quantitatively and in immunoblot analyses to determine qualitatively the subclass antibody specificities. Quantitatively, the most significant differences among patient groups were in levels of IgG4, which were more than 17 times higher in MF patients (geometric mean, 64.7 micrograms/ml) than in those with CP (mean, 3.7 micrograms/ml). When qualitative analyses were done on the same sera, major differences were noted, particularly in the recognition profiles of the IgG1, IgG3, and IgG4 responses. IgG1 and IgG3 responses to antigens were seen especially to antigens with m.w. greater than 68,000 in all patients with elephantiasis, whereas MF patients showed most of their reactivity to antigens less than 68,000. For IgG4, the MF patients showed prominent recognition of antigens throughout the entire range of m.w., whereas those with CP had very little IgG4 recognition of antigens of any m.w. Interestingly, this relationship was essentially reversed in the IgG3 antibody responses (especially to antigens greater than 68,000) and, to a lesser extent, the IgG1 responses. These findings demonstrate correlations of potential cause/effect significance between IgG4 antibody responsiveness and the immunomodulated asymptomatic MF form of clinical filariasis and between IgG3/IgG1 antibody responsiveness and the clinical presentation of CP.

IgG antibody subclasses in human filariasis. Differential subclass recognition of parasite antigens correlates with different clinical manifestations of infection

The four subclasses of IgG are distinct in structure, function, and degree of participation in the antibody response to complex antigens. Looking for differential responsiveness of potential pathogenetic significance, we have analyzed both quantitatively and qualitatively the filaria-specific IgG subclass responses of 20 patients with lymphatic filariasis presenting either with chronic lymphatic obstructive pathology and elephantiasis (CP) or with asymptomatic microfilaremia (MF). Subclass-specific monoclonal antibodies were used in an enzyme-linked immunosorbent assay to study IgG filarial antibodies quantitatively and in immunoblot analyses to determine qualitatively the subclass antibody specificities. Quantitatively, the most significant differences among patient groups were in levels of IgG4, which were more than 17 times higher in MF patients (geometric mean, 64.7 micrograms/ml) than in those with CP (mean, 3.7 micrograms/ml). When qualitative analyses were done on the same sera, major differences were noted, particularly in the recognition profiles of the IgG1, IgG3, and IgG4 responses. IgG1 and IgG3 responses to antigens were seen especially to antigens with m.w. greater than 68,000 in all patients with elephantiasis, whereas MF patients showed most of their reactivity to antigens less than 68,000. For IgG4, the MF patients showed prominent recognition of antigens throughout the entire range of m.w., whereas those with CP had very little IgG4 recognition of antigens of any m.w. Interestingly, this relationship was essentially reversed in the IgG3 antibody responses (especially to antigens greater than 68,000) and, to a lesser extent, the IgG1 responses. These findings demonstrate correlations of potential cause/effect significance between IgG4 antibody responsiveness and the immunomodulated asymptomatic MF form of clinical filariasis and between IgG3/IgG1 antibody responsiveness and the clinical presentation of CP.

The clinical and immunologic responses of normal human volunteers to low dose hookworm (Necator americanus) infection

Five normal human volunteers were exposed to approximately 50 infective larvae of Necator americanus and were observed for the development of clinical signs or symptoms and for changes in blood eosinophil levels, IgG antibody titers, total and parasite-specific IgE, and lymphocyte blastogenic responses for 6-10 weeks. Bronchoalveolar lavage was performed on four subjects prior to infection and at times when larval migration through the pulmonary tree was likely. Eggs were demonstrated in the stools of four volunteers who remained untreated for more than 6 weeks; one volunteer had to be treated at day 40 because of severe gastrointestinal symptoms. All others also complained of abdominal pain and flatulence between days 35-40. All volunteers developed marked blood eosinophilia which peaked between days 38-64 and ranged from 1,350-3,828 eosinophils/mm3. Small increases in total and parasite-specific IgE and IgG were noted in some volunteers. One volunteer showed a significant lymphocyte blastogenic response. With the exception of mucosal erythema, bronchoalveolar lavage results were unremarkable. Our data indicate that a single small inoculum of hookworm larvae is capable of producing significant transient gastrointestinal morbidity and marked blood eosinophilia but does not induce other prominent T cell- and B cell-dependent immune responses.

An analysis of in vitro B cell immune responsiveness in human lymphatic filariasis

The immunoregulatory mechanisms involved in B cell function in patients with varying clinical manifestations of bancroftian filariasis were examined by studying the ability of peripheral blood mononuclear cells (PBMC) or PBMC subpopulations from patients with elephantiasis, asymptomatic microfilaremia (MF), and acute tropical pulmonary eosinophilia (TPE) to produce polyclonal and parasite-specific antibody in vitro, both spontaneously and in response to a mitogen (PWM) and to parasite antigen. When the spontaneous or mitogen-driven polyclonal responses were examined, all groups produced significant amounts of IgM and IgG; those with TPE produced extremely high levels. However, when in vitro parasite antigen-specific responses were examined, those with MF were unable to produce filaria-specific antibody either spontaneously or in response to PWM or parasite antigen; in contrast, patients with chronic lymphatic obstruction or TPE produced large quantities. Removal of neither adherent cells nor T8+ T cells affected the parasite-specific B cell anergy seen in those with MF. This absent or severely diminished capacity to produce antibody on parasite antigenic stimulation in patients with MF is likely responsible for the low levels of parasite-specific antibody seen in this most common clinical manifestation of bancroftian filariasis. Its inability to be reversed by the removal of "suppressor elements" suggests a state of B cell unresponsiveness to the parasite.

An analysis of in vitro B cell immune responsiveness in human lymphatic filariasis

The immunoregulatory mechanisms involved in B cell function in patients with varying clinical manifestations of bancroftian filariasis were examined by studying the ability of peripheral blood mononuclear cells (PBMC) or PBMC subpopulations from patients with elephantiasis, asymptomatic microfilaremia (MF), and acute tropical pulmonary eosinophilia (TPE) to produce polyclonal and parasite-specific antibody in vitro, both spontaneously and in response to a mitogen (PWM) and to parasite antigen. When the spontaneous or mitogen-driven polyclonal responses were examined, all groups produced significant amounts of IgM and IgG; those with TPE produced extremely high levels. However, when in vitro parasite antigen-specific responses were examined, those with MF were unable to produce filaria-specific antibody either spontaneously or in response to PWM or parasite antigen; in contrast, patients with chronic lymphatic obstruction or TPE produced large quantities. Removal of neither adherent cells nor T8+ T cells affected the parasite-specific B cell anergy seen in those with MF. This absent or severely diminished capacity to produce antibody on parasite antigenic stimulation in patients with MF is likely responsible for the low levels of parasite-specific antibody seen in this most common clinical manifestation of bancroftian filariasis. Its inability to be reversed by the removal of "suppressor elements" suggests a state of B cell unresponsiveness to the parasite.