Dirofilaria immitis. VI. Antimicrofilarial immunity in experimental filariasis

Antimicrofilarial immunity was studied in Dirofilaria immitis-infected dogs in order to better understand amicrofilaremic filariasis in man. Sera from dogs with amicrofilaremic infections contained IgG antibodies specific for microfilarial surface antigens detectable by immunofluorescence and in vitro leukocyte adherence. In vivo immune mechanisms were studied by injecting 51Cr-labeled microfilariae (MF) into infected and uninfected dogs. Injected MF were concentrated in lung, liver, spleen, and kidneys of normal and microfilaremic dogs, but circulated throughout the 5-hour study period. In contrast, injected MF were rapidly cleared (15-30 min) from the blood of amicrofilaremic-infected dogs. Tissue radioactivity and histopathology indicated that injected MF were trapped and destroyed in the lungs of these dogs. Antibody-dependent clearance and destruction of MF is a potent anti-helminth effector mechanism in canine dirofilariasis. Similar events are likely to occur in amicrofilameric filariasis in humans.

Effects of infused histamine: correlation of plasma histamine levels and symptoms

Plasma and urine histamine levels were measured during sequential infusions of histamine (0.05, 0.1, 0.25, 0.5, and 1.0 microgram/kg/min histamine base for 30 min each) to determine the plasma level required to elicit flushing, headaches, tachycardia, and diastolic hypotension. Each study was performed with subjects on no medications or after pretreatment with hydroxyzine and/or cimetidine in order to confirm the receptor subtype involved in each of the responses. Resting plasma histamine levels were 0.62 +/- 0.12 ng/ml, and levels rose progressively indirect proportion to the concentration of infused histamine. Plasma levels of histamine required to elicit symptoms were as follows: 1.61 +/- 0.30 ng/ml = 30% increase in heart rate, 2.39 +/- 0.52 ng/ml = significant flush and headache, and 2.45 +/- 0.13 ng/ml = 30% increase in pulse pressure. Cimetidine pretreatment failed to influence the histamine level required to elicit symptoms, hydroxyzine pretreatment significantly raised the level required to increase heart rat by 30%, and the combination of antihistamines significantly raised the threshold for histamine to elicit all the response. Urine histamine was increased in direct proportion to the histamine infusions, and because of stability, accessibility, and the capacity for retrospective diagnosis, urine is the suggested fluid to employ to measure histamine release in humans.

IgE antibodies are more species-specific than IgG antibodies in human onchocerciasis and lymphatic filariasis

To explore the relative species specificities of the IgE and IgG antibody responses to helminth infections in man, we studied four pools of sera from patients infected with Wuchereria bancrofti, Brugia malayi, Onchocerca volvulus or Ascaris lumbricoides and ten individual sera from patients with onchocerciasis. IgE antibodies were detected by radioallergosorbent test (RAST) analysis and IgG antibodies by a Staphylococcus protein A radioimmunoassay (Staph A-RIA). Analysis of the binding curves with four different immunosorbents (prepared from antigens of B. malayi, O. volvulus, Dipetalonema viteae and A. lumbricoides) in the RAST and the binding curves with these same four antigens in the Staph A-RIA confirmed the relative species specificities for both the IgE and IgG antibody responses. Then determination of these antibody levels after specific absorption of the sera with both homologous and heterologous antigens showed that in all instances there was significantly less cross-reactivity with heterologous parasite antigens (i.e. higher species specificity) in the IgE antibody response to filarial infection than in the corresponding IgG antibody response. Such findings imply that efforts toward developing techniques for specific immunodiagnosis of filarial infections are likely to be particularly successful if focused on the IgE antibody response of exposed individuals.

Schistosoma mekongi infection in man: cellular immune responses and modulating mechanisms

Cell-mediated immune responses (CMI), as assessed by lymphocyte proliferation in vitro, were evaluated in 11 Laotian patients harbouring asymptomatic chronic infections by Schistosoma mekongi, a schistosome closely related to S. japonicum. When the mononuclear cells of these patients were cultured in autologous plasma, lymphocyte responses to schistosome antigens were essentially nil, not differing from those of unexposed North American controls. Specific lymphocyte proliferation, however, was seen both after the removal of mononuclear cells that were nylon-wool-adherent and after substitution of the autologous serum in the culture with normal AB serum. Our data suggest that the CMI responses of humans with chronic S. mekongi infections are 'modulated' by adherent suppressor cells and serum-suppressive factors, and that modulation of CMI supports the stable host-parasite relationship in a similar fashion to that described for chronic human Schistosoma mansoni infection.

Detection, quantitation, and specificity of antiparasite IgE antibodies in human schistosomiasis mansoni

Sera from 15 patients with acute or chronic Schistosoma mansoni infection were evaluated for IgE antibodies directed against soluble cercarial, adult worm, and egg antigens. Both the antigen-induced release of histamine from passively sensitized human basophils and specific radioimmunoassays were used to detect these IgE antibodies, and determination of serum IgE levels before and after specific immunosorption permitted their quantification. While chronically infected patients made IgE antibodies to all three stages of the parasite, only egg antigens induced an appreciable IgE antibody response in acutely infected individuals. Despite the fact that patients with chronic infection had significantly greater levels of total serum IgE than patients with acute disease, the percentage of this IgE that was parasite specific was similar for both groups, ranging between 4% and 28%. An ancillary observation was the fact that soluble egg antigen can trigger basophil histamine release through IgE-dependent reactions and through "nonimmunologic" mechanisms that require further characterization.

Infection with Schistosoma mekongi in Southeast Asian refugees

Schistosoma mekongi is a newly recognized species of Schistosoma that is closely related to Schistosoma japonicum and is pathogenic to humans. Like the other forms of schistosomiasis in which the parasites reside in the mesenteric vasculature, S. mekongi infection has hepatosplenomegaly and portal venous hypertension as its most common serious sequelae. Schistosomiasis, although endemic in certain areas of Southeast Asia, has not been recognized as a health problem in Asian refugees who are currently entering the United States. In the present study 12 Laotian immigrants with S. mekongi infection were examined. The clinical, laboratory, and parasitologic findings in these patients are discussed. The diagnosis was made by examination of stool specimens in 11 patients and rectal biopsy specimens in one patient. All patients were asymptomatic, although the six youngest children had hepatomegaly. It is suggested that specific serologic tests may be useful in screening Asian refugees for infection with Schistosoma.

IgE responses in human filariasis. I. Quantitation of filaria-specific IgE

We have developed a noncompetitive solid phase radioimmunoassay to quantitate human IgE antibodies against soluble adult antigens of Brugia malayi (B.m.), a filarial parasite, in sera of patients with various forms of clinical filariasis in Madras, India. A single reference serum was shown to contain 23 micrograms/ml of B.m.-specific IgE by depletion analysis and was used as a standard serum throughout the study. The levels of specific IgE ranged in the patients sera from 2 to 23,000 ng/ml. When these individuals were divided into clinical groups, the individuals with tropical pulmonary eosinophilia had the highest levels (mean = 8630 ng/ml) and were significantly higher than all the other groups (p less than 0.001). The lowest levels were seen in patients with circulating microfilariae (mean = 30.5 ng/ml). Patients exhibiting lymphatic obstruction (i.e., chronic pathology group) had levels slightly higher than microfilaremics (mean = 68 ng/ml) but were not significantly different (p less than 0.1). Surprisingly, individuals living in endemic areas but who had no clinical signs of filariasis also showed appreciable levels of B.m.-specific IgE (mean = 55 ng/ml). The B.m.-specific IgE represented 0.1 to 48% of the total IgE. High percentages of specific IgE may be responsible for evoking allergic symptomatology in patients with tropical pulmonary eosinophilia.

IgE responses in human filariasis. I. Quantitation of filaria-specific IgE

We have developed a noncompetitive solid phase radioimmunoassay to quantitate human IgE antibodies against soluble adult antigens of Brugia malayi (B.m.), a filarial parasite, in sera of patients with various forms of clinical filariasis in Madras, India. A single reference serum was shown to contain 23 micrograms/ml of B.m.-specific IgE by depletion analysis and was used as a standard serum throughout the study. The levels of specific IgE ranged in the patients sera from 2 to 23,000 ng/ml. When these individuals were divided into clinical groups, the individuals with tropical pulmonary eosinophilia had the highest levels (mean = 8630 ng/ml) and were significantly higher than all the other groups (p less than 0.001). The lowest levels were seen in patients with circulating microfilariae (mean = 30.5 ng/ml). Patients exhibiting lymphatic obstruction (i.e., chronic pathology group) had levels slightly higher than microfilaremics (mean = 68 ng/ml) but were not significantly different (p less than 0.1). Surprisingly, individuals living in endemic areas but who had no clinical signs of filariasis also showed appreciable levels of B.m.-specific IgE (mean = 55 ng/ml). The B.m.-specific IgE represented 0.1 to 48% of the total IgE. High percentages of specific IgE may be responsible for evoking allergic symptomatology in patients with tropical pulmonary eosinophilia.

Familial predisposition to filarial infection--not linked to HLA-A or-B locus specificities

Two hundred and twenty-five Polynesians were selected from a larger study population for the evaluation of potential genetic influences on the susceptibility to bancroftian filariasis. Analysis showed that there was significantly familial clustering of patients with filariasis and that this clustering was most compatible with genetic transmission of disease susceptibility. The data best fit a model in which the hypothetical gene for filariasis was recessive with a frequency of 0.82 +/- 0.15 in the population and a penetrance of 0.62 +/- 0.14. The alternative hypothesis that susceptibility was environmentally (i.e., not genetically) determined was also compatible with the data but was estimated to be 1.9 times less likely to account for the observed findings than the genetic hypothesis. Extensive evaluation of HLA-A and -B locus specificities failed to detect significant linkage either between particular antigen specificities and the clinical manifestations of filariasis or between individual haplotypes (indicated by HLA markers in studies of large families) and the predisposition to filarial infection or disease.

The quantitation of parasite-specific human IgG and IgE in sera: evaluation of solid-phase RIA and ELISA methodology

We have developed a non-competitive solid-phase radioimmunoassay (SPRIA) to quantitate both human IgE and IgG antibodies against soluble adult antigens of Brugia malayi (B.m.), a filarial parasite causing extensive infection throughout the tropics. Previously enzyme-linked immunosorbent assays (ELISA) had been used to detect microgram/ml levels of IgG anti-B.m., but IgE antibodies were difficult to detect in this system. Since the SPRIA successfully quantitates both IgG and IgE anti-B.m., we sought to examine the reasons for the SPRIA's apparent superiority in detecting IgE anti-B.m. by extracting specific IgG from sera with high levels of IgE and IgG anti-B.m. antibodies. IgE anti-B.m. was then quantitated in these sera using both the SPRIA and ELISA methods. Results indicate that IgG anti-B.m. does not interfere with detection of specific IgE antibody in the SPRIA but does interfere in the ELISA. While ELISA permits detection of IgE anti-B.m. in the absence of competing IgG anti-B.m., as levels of specific IgG increase, the IgE is no longer detectable. These differences between SPRIA and ELISA can be explained by the SPRIA's antigen excess conditions which assure that there are sufficient antigens both to detect all anti-B.m. antibodies present in the serum and to adequately represent all antigen specificities in the crude B.m. extract. Our findings commend the use of SPRIA methods over ELISA in assessment of B.m.-specific IgE antibody in filariasis and indicate a potential role for SPRIA methods in absolute quantitation of specific serum antibodies.

Serial observations of circulating immune complexes in patients with acute schistosomiasis

To define further the role of circulating immune complexes in acute schistosomiasis, serial determinations of [125I]Clq binding activity (ClqBA) in 15 patients with this disease were made before and after treatment with niridazole. Levels of ClqBA were elevated in 13 of these patients and in general rose early in the course of disease, reaching maximal levels by 10 weeks after exposure; the levels were correlated with disease severity (r = 0.70, P less than 0.01) and with the concentration of Schistosoma mansoni eggs in the stool (r = 0.59, P less than 0.05). The rise and fall in levels of ClqBA was associated in most instances with the temporal course of other laboratory values reflecting disease activity. The close association of circulating immune complexes with measures of disease activity suggests that these complexes are important in the pathogenesis of acute schistosomiasis.

Cercaria-induced histamine release: a factor in the pathogenesis of schistosome dermatitis?

Cercariae, but not schistosomules, of Schistosoma mansoni are capable of activating the release of histamine from rat peritoneal mast cells in vitro. This activation occurs in the absence of serum and does not require adherence to mast cells. The amount of histamine released is proportional to the number of cercariae present. This mast-cell triggering factor from cercariae remains to be characterized biochemically, but may well play a causal role in the "swimmer's itch" associated with primary schistosome exposure.

Immediate and delayed hypersensitivity skin test responses to the Dirofilaria immitis filarial skin test (Sawada) antigen in Wuchereria bancrofti filariasis

In order to assess the immunodiagnostic utility of FST skin test antigen purified from Dirofilaria immitis, skin test responses were analyzed in 177 inhabitants of a South Pacific island hyperendemic for Wuchereria bancrofti filariasis. Although the distribution of immediate hypersensitivity skin test responses was similar to those found in other filarial endemic populations, individual immediate skin test reactions lacked the sensitivity and specificity to identify those with microfilaremia or those with any clinical or parasitologic evidence of filarial disease. Delayed hypersensitivity type skin test reactions were elicited by the antigen in 60% of people but again these delayed cutaneous reactions did not correlate with the presence or absence of stigmata of filariasis. These findings document the limitation of this antigen preparation in the immunodiagnosis of filariasis in residents of an endemic area.

Modulation of the host response in human schistosomiasis. II. Humoral factors which inhibit lymphocyte proliferative responses to parasite antigens

Humoral suppressive factors were identified in the plasma of 13 of 14 patients with schistosomiasis mansoni. These factors suppressed lymphocyte proliferative responses to parasite antigens but did not affect lymphocyte responses to either nonparasite antigens or mitogens. Furthermore, they had no inhibitory effect on proliferative responses of lymphocytes of normal, noninfected individuals. Three patients studied sequentially before and after therapy with niridazole developed positive lymphocyte responses to parasite antigens within the first month of treatment, but this enhanced responsiveness was not accompanied by clearance of these humoral supressive elements, which persisted in the patients' plasmas. Such suppressive factors which are specific for responses to parasite antigens probably form one of the mechanisms which determine the state of partial immunosuppression found in patients with chronic schistosome infection.

Enzyme-linked immunosorbent assay (ELISA) for detecting IgM and IgE antibodies in human schistosomiasis

Sera from patients with acute or early and chronic schistosomiasis were examined for IgG, IgM, and IgE antibody by an enzyme-linked immunosorbent assay technique, using soluble egg antigen from Schistosoma mansoni. Cercarial/adult IgG antibody ratios were determined, using soluble cercarial and adult worm antigens. Sera with cercarial/adult ratios indicative of acute or early schistosomiasis also contained specific IgM antibodies. Schistosome IgE antibody was found in sera from patients with acute schistosomiasis, but in only 1 of 10 sera from patients with chronic schistosomiasis. The inability of ELISA to detect IgE antibodies in chronic sera indicates that it may be a relatively insensitive measure of IgE antibodies in those patients with chronic schistosomiasis.

Circulating immune complexes in acute schistosomiasis

The sera of patients with acute and chronic schistosomasis were tested for the presence of circulating immune complexes with the 125I-Clq binding assay. Fourteen out of fifteen (93%) patients with acute schistosomiasis had elevated 125I-Clq binding activity, while only two out of eleven (18%) patients with chronic disease had C1q binding complexes. This difference was significant (P less than 0.001) and paralleled the degree of clinical didsease activity between the two groups of patients. IgG and IgM were readily detected in all of these circulating complexes but the specific parasite antigens initiating their formation could not be defined. The level of circulating immune complexes was inversely correlated with the absolute eosinophil counts for individuals in the acutely infected group, an observation compatible wiht the hypothesis that a functional role for the eosinophil is the destruction and elimination of immune complexes.