Evidence for IgE-dependent cytotoxicity by rat eosinophils

Human and rodent eosinophils have been shown previously to act as effector cells against Schistosoma mansoni schistosomula by ADCC mechanisms involving IgG antibodies. The present work brings novel evidence for the existence in rat schistosomiasis of an IgE-eosinophil dependent cytotoxicity mechanism. The role of IgE antibodies present in the rat serum after 6 weeks of infection was clearly established by immunoadsorption and inhibition experiments, whereas the participation of IgG and complement in this system could be ruled out. Mast cell products, including ECF-A tetrapeptides, appear to play an essential role in significantly increasing eosinophil cytotoxicity. A kinetic study of the IgG-dependent cytotoxicity mechanism previously described and of this IgE-mediated mechanism according to rat schistosomiasis revealed the preeminent role played by IgG antibodies in early infection, whereas IgE predominated after 6 wk of infection. The possible significance of IgE-eosinophil cooperation in ADCC mechanisms in parasite and nonparasite models is discussed.

Tetrapeptides of the eosinophil chemotactic factor of anaphylaxis (ECF-A) enhance eosinophil Fc receptor

Certain mast cell products, including the tetrapeptides Ala-Gly-Ser-Glu (Ala4) and Val-Gly-Ser-Glu (Val4) of the eosinophil chemotactic factor of anaphylaxis (ECF-A) and histamine, are preferentially chemotactic for eosinophils in vitro. Amino acid substitutions or modifications of the ECF-A tetrapeptides may substantially alter the chemotactic activity of human eosinophils. The cellular mechanism whereby ECF-A tetrapeptides enhance IgG-dependent killing of schistosomula by rat eosinophils is, however, unclear. We now report that the parent tetrapeptides and the substituted analogue Val-Pro-Ser-Glu (Pro3), but not histamine, increase the number of rat and human eosinophils that form rosettes with erythrocytes bearing IgG antibodies. Moreover, we find a correlation between the effect of these substances on the expression of rat eosinophil IgG Fc receptors and their capacity to increase the IgG-dependent cytotoxicity of rat eosinophils for Schistosoma mansoni schistosomula.

Dipetalonema viteae infective larvae reach reproductive maturity in rats immunodepressed by prior exposure to Schistosoma mansoni or its products and in congenitally athymic rats

Infective larvae of Dipetalonema viteae did not reach maturity in inbred Fischer rats. However, female adults of D. viteae when transplanted surgically into Fischer rats established and the resulting microfilaraemia from the transplanted worms persisted for about 120 days after infection. Sequential dissections showed that some of the female worms transplanted remained viable in rats for about 35 days after infection. After inoculation of infective larvae into rats a varying number transformed into stage-4 larvae but they did not develop into adult worms and were killed. However, when the rats were immunodepressed non-specifically by a pre-existing Schistosoma mansoni infection or by treatment with S. mansoni-derived substance(s), a number of stage-4 larvae renewed their development and reached sexual maturity. These worms produced microfilariae which were observed in the peripheral blood for about 40 days. The effect of previous infection with S. mansoni on the survival and growth of D. viteae in Fischer rats depends greatly on the relative timing of infection because infective larvae of D. viteae reached maturity only when rats were inoculated with infective larvae after 15 days of S. mansoni infection but not after 21 or 28 days of S. mansoni infection. D. viteae will also develop to maturity in congenitally athymic rats. In congenitally athymic rats (Nu/Nu) each given 75 infective larvae, both the microfilaraemia and adult worm recovery at post-mortem were higher than those which resulted in Nu/Nu rats given an infection of 200 larvae. These experiments show that in rats innate immunity to this filarial nematode reflects a very rapidly induced acquired immunity which kills the parasite before it reaches maturity.

Role of anaphylactic antibodies in immunity to schistosomes

Antibody-dependent cell-mediated cytotoxicity in reinfection immunity to schistosomes in the rat involves either IgG2a anaphylactic antibody and eosinophils or IgE antibody and macrophages. The first system requires two signals, one by the antibody through the eosinophil Fc receptor, another by mast cells through the release of mediators among which is ECF-A. IgE antibody complexed with schistosome antigen binds to an IgE-specific receptor on the macrophage and triggers the cell to release enzymes and superoxide. Immunity in rat schistosomiasis is antibody-dependent, abolished in anti-mu treated neonate rats or by passive serum transfer after selective depletion of either IgG2a or IgE. The two anaphylactic antibody-dependent cell cytotoxicity systems are in a permanent balance in immune rats, eosinophils being blocked by IgG2a immune complexes when this cell is inefficient. Anaphylactic antibodies thus play a key role in triggering and modulating effector cell function.

In vitro study of immunological events in human and experimental schistosomiasis: relationships between cytotoxic antibodies and circulating Schistosoma antigens

Complement-dependent cytotoxic antibodies were found in 54% of Schistosoma mansoni infected patients from Burundi and in 69 to 78% of Schistosoma mansoni ninfected Brazilian patients. The levels of cytotoxic Ab were not statistically different in sera from infected mothers and from their newborn children, suggesting a transfer through the placenta. A sandwich radioimmunoassay (SRIA) and the Radioimmunoprecipitaion-PEG assay (RIPEGA) technique were used in order to detect respectively total schistosome circulating soluble antigens (CSA) and schistosome antigen '4' in sera from infected patients. An inverse relationship was found between the presence of cytotoxic Ab and both total CSA and antigen '4'. The cytotoxic Ab and total CSA levels were followed in five Erythrocebus patas monkeys for 30 weeks after Schistosoma mansoni infection. As in human schistosomiasis the presence of cytotoxic Ab was found to be inversely correlated with the presence of total CAS. The blocking role of Schistosoma mansoni antigens in a complexed form was suggested by the inhibitory effect of the ultracentrifugation pellet of infected human serum on the cytotoxic activity. Moreover, the CSA absorption of infected monkey serum by passage through an anti-CSA immunosorbent significantly increased the cytotoxic activity. Possible mechanisms for the inhibitory role of circulating immune complexes on complement-dependent cytotoxic activity are discussed.

Complement studies in BN rats with mercuric chloride-induced immune glomerulonephritis

Whole complement haemolytic activity (CH50) changes were examined in 71 rats, developing and HgCl2-induced biphasic immune glomerulonephritis. In some rats, serum C4 level was also studied. Whole CH50 level was compared with proteinuria and C3 glomerular deposits. In control rats or in rats injected with low doses of HgCl2, there was no complement decrease. In rats injected with a high dose, after an initial increase (also observed in controls), CH50 level decreased between day 12 and day 20, sometimes dramatically. This decrease, observed during the first phase, was transient, CH50 levels returning to normal before day 30. Serum C4 level varied in accordance with CH50, indicating a classical pathway activation of complement. Fall in CH 50 and proteinuria was correlated: the heavier the proteinuria, the greater the fall in complement (p < 0.01). Whether proteinuria is or is not the consequence of the complement activation, remains to be demonstrated.

IgE antibody-mediated cytotoxicity of rat macrophages against microfilaria of Dipetalonema citeae in vitro

The Fischer rat develops an acquired resistance against circulating microfilariae. Macrophages from the peritoneal washings of normal rats preincubated at 37 degrees C with the sera obtained from rats immune to circulating microfilariae adhered to and kill the microfilaria of Dipetalonema viteae in vitro within 16 to 24 hr. No significant adherence and cytotoxicity was mediated by sera collected from animals with microfilaraemia or from normal rats. Adherence of macrophages to microfilaria was associated with damage to the surface of the larva as revealed by ultrastructural studies. Neither adherence nor cytotoxicity was induced by preincubation of microfilariae, instead of macrophages with immune serum. The serum factor which mediated adherence and cytotoxicity was heat-labile, but was not a complement component. Immune absorption experiments showed that the relevant serum factor resided in the IgE class of antibody. The immune adherence to D. viteae by macrophages is stage-specific because adherence to infective larvae was not observed whether rate macrophages were preincubated in sera obtained from rats immune to microfilariae or in sera collected from animals after exposure to infective larvae.

Effect of neonatal injection of anti-mu antibodies on immunity to schistosomes (S. mansoni) in the rat

The effect of neonatally initiated injections of anti-mu serum on immunity to reinfection with Schistosoma mansoni in the rat was investigated in vitro and in vivo. Anti-mu treatment resulting in a profound depression of immunoglobulin synthesis dramatically decreased immunity to reinfection assessed by worm recovery technique. Complement-dependent antibody, IgG2a antibody-eosinophil-mediated and IgE-macrophage cytotoxicity reactions were in parallel markedly reduced. These results show the prominent role played by antibody-dependent mechanisms in immunity to schistosomes in the rat.

Effect of neonatal injection of anti-mu antibodies on immunity to schistosomes (S. mansoni) in the rat

The effect of neonatally initiated injections of anti-mu serum on immunity to reinfection with Schistosoma mansoni in the rat was investigated in vitro and in vivo. Anti-mu treatment resulting in a profound depression of immunoglobulin synthesis dramatically decreased immunity to reinfection assessed by worm recovery technique. Complement-dependent antibody, IgG2a antibody-eosinophil-mediated and IgE-macrophage cytotoxicity reactions were in parallel markedly reduced. These results show the prominent role played by antibody-dependent mechanisms in immunity to schistosomes in the rat.

Identification and measurement of rat eosinophil phospholipase D. Its activity on schistosomula phospholipids

A sensitive assay, using [14C]lecithin as a substrate, has been developed for the measurement of phospholipase activity in rat peritoneal polymorphonuclear leukocytes. Cell extracts were found to contain a phospholipase D activity and indirect evidence suggested that eosinophils are responsible for the cleavage of lecithin. Intact peritoneal cells were also able to hydrolyze exogenous [14C]lecithin in vitro. When [3H]choline-labeled schistosomula were used as targets in antibody-dependent cytotoxicity experiments, the radioactivity of lecithin decreased more rapidly in a complete cytotoxicity system than in controls, suggesting that hydrolysis of schistosomula phospholipids occurred during the killing process.

[The immunological diagnosis of hydatidosis. 139 cases (author's transl)]

Hydatidosis is not rare in France and often poses diagnostic problems to practitioners. In addition to classical clinical and radiological data, immunological methods provide at the present time reliable means of confirming the diagnosis and conducting post-therapeutic surveillance. After a brief epidemiological and clinical review, the authors review the different laboratory techniques available and report their experience involving 139 cases collected over a period of 2 years. Emphasis is placed upon the relatively high prevalence of the disease amongst immigrant workers, as oppossed to the rare cases seen in the native population, as well as the value of immunoelectrophoresis and conditioned haemagglutination reactions. New therapeutic possibilities offered by mebendazole and its derivatives are indicated.

In vitro and in vivo inhibition of mast cell degranulation by a factor from Schistosoma mansoni

Schistosome incubation product (SIP) obtained from <i>Schistosoma mansoni</i> was tested on mast cell degranulation <i>in vitro</i> or <i>in vivo</i> elicited by chemical compounds or anaphylactic reactions. Normal mast cells from Wistar rats were labeled with ³H-serotonin and incubated with the SIP. Serotonin release normally induced by the chemical compounds 48/80, polymyxin B or an anaphylactic system (ovalbumin-antiovalbumin) was inhibited when mast cells were preincubated with the SIP. Cutaneous reactions elicited by the compound 48/80 or polymyxin B and passive or active cutaneous anaphylactic reactions, were inhibited by the intradermal injection of the SIP before the challenge. The anaphylactic shock by ovalbumin was also inhibited in guinea pigs by a previous intraperitoneal injection of the SIP. This inhibitor appeared dialysable, heat resistant and soluble in trichloroacetic acid (TCA). The inhibitory activity was found in the fraction eluted from an antischistosome immunosorbent. However, no inhibition of cutaneous reactions was observed with the circulating (TCA-soluble, thermostable) M antigen previously described and purified from schistosomes. No effect of the SIP was observed on the growth of HeLa cells or the J 111 human monocytic cell line. The increase of intracellular cAMP levels in mast cells incubated with the SIP suggests that modulation of cAMP is involved in the mechanism of inhibition. The SIP inhibited also the mast cell-dependent eosinophil cytotoxicity for schistosomula sensitized with IgG2a antibody. The SIP appeared to act selectively on mast cell degranulation without effect on eosinophils or the mast cell mediators. This inhibitor, denominated schistosome-derived inhibitory factor, released by the parasite, which acts on mast cells could partly explain the low incidence of clinical allergic manifestations observed in parasitic diseases and might represent an escape mechanism of the parasite to the antibody-dependent eosinophil cytotoxicity mechanism.

In vitro killing of S. mansoni schistosomula by eosinophils from infected rats: role of cytophilic antibodies

The cytotoxic effect of peritoneal cells from Schistosoma mansoni-infected rats against antibody-opsonized or nonopsonized schistosomula in vitro has been studied during the course of infection. Eosinophil-enriched cell preparations were shown to have a high cytotoxic effect on schistosomula in the absence of antibody. The killer cells were identified as eosinophils. As in the ADCC mechanism previously described, mast cell-eosinophil interaction was required for eosinophil cytotoxicity. Rosette formation using S. mansoni antigen-coated erythrocytes was used to demonstrate the presence of anti-S. mansoni IgG2a antibody at the surface of infected eosinophils. Passive sensitization of normal eosinophils with ultracentrifugation pellets of immune rat serum resulted in a significant cytotoxicity of sensitized eosinophils. A close relationship was found between the cytotoxic activity of infected cells and the ability of the corresponding infected serum to arm normal eosinophils. At certain periods after infection, eosinophils from infected rats were less effective than normal eosinophils on antibody-coated schistosomula. EA- (rat) rosetting assay and blockade experiments with homologous immune complexes have revealed in a kinetic study that the blocking of cytotoxic activity of infected eosinophils was related to heat-stable circulating immune complexes. The possible role of immune complexes either in arming or inhibiting effector cells is suggested.

[Production of monoclonal anti-Schistosoma mansoni antibodies. Preliminary study of their biological activities]

Monoclonal antibodies against Schistosoma mansoni have been produced by fusion of splenic lymphocytes from S. mansoni infected Rats and P3-X63-Ag8 BALB/c cells. In vitro and in vivo studies of the biological activities of these antibodies have led to the identification of IgE antibodies with a high reaginic activity and antibodies which in a complement dependent or eosinophil dependent system were shown to have a marked cytotoxicity for schistosomula in vitro. This methodology seems to open new perspectives for the study of antibody function in immunity against parasites as well as for the isolation of the corresponding target antigens.

Activation of complement by Schistosoma mansoni schistosomula: killing of parasites by the alternative pathway and requirement of IgG for classical pathway activation

Living Schistosoma mansoni schistosomula incubated with normal chicken, guinea pig, human, and monkey sera were killed after 4 hr contact at 37 degrees C. The following data indicate that this action is dependent on the activation of the alternative complement pathway (AP): a) the inactivity of RB, RD, and zymosan-treated serum against schistosomula; b) the partial activity of RD restored in FD; c) the full effect of the C4-deficient guinea pig, C2-deficient human, and the agammaglobulinemic human sera; d) the consumption of both the AP and FB after the incubation of NHS with schistosomula; e) the detection of C3d breakdown product during the contact of the C2-deficient human serum with these young parasites. Killing by serum was decreased as the immature schistosomes developed and was completely absent against 4-day-old lung schistosomula (LS). In other experiments, it was demonstrated that schistosomula, in the presence of IgG, were able to initiate complement activation also through the classical pathway (CP). However, the CP does not appear to play a role in the schistosomulicidal activity of complement. The in vivo relevance of these observations is considered.

Rat mast cell-eosinophil interaction in antibody-dependent eosinophil cytotoxicity to Schistosoma mansoni schistosomula

The involvement of IgG2a antibodies and mast cells in antibody-dependent eosinophil cytotoxicity suggested a possible interaction between mast cells and eosinophils for in vitro killing of Schistosoma mansoni schistosomula. Cell purification procedures showed that a minimum ratio of mast cells was required to obtain eosinophil cytotoxicity. The incubation of mast cells with heat-aggregated IgG2a immunoglobulins before addition to a mast cell-depleted eosinophil population induced a significant degree of inhibition of cytotoxicity, Similarly, the heat-aggregated IgG2a Fc fragment had a strong inhibitory effect whereas incubation of mast cells with Fab fragment failed to inhibit the cytotoxic effect. The Fc portion of IgG2a immunoglobulins therefore seemed to be involved in binding to the mast cell surface. Furthermore, it was demonstrated that soluble mediators released after mast cell activation either by compound 48/80, or by IgE, or IgG2a-dependent reaction had the same effect as intact mast cells. These observations suggest that the eosinophil-dependent cytotoxicity mechanism requires a signal provided by soluble mast cell mediators in addition to antibody.

IgE in experimental schistosomiasis. II. Quantitative determination of specific IgE antibodies against S. mansoni: a follow-up study of two strains of infected rats. Correlation with protective immunity

Parasite specific IgE antibodies in rats infected with Schistosoma manoni were measured by passive cutaneous anaphylaxis (PCA) reactions and by the technique of immuno-adsorption. Two strains, one a low IgE producer (Fischer rats) and the other a high IgE producer (Hooded-Lister rats) were studied. In Fischer rats, a time course study of the occurrence of IgE antibodies and resistance to reinfection was made. Parasite specific IgE levels measured by immuno-adsorpiton were much lower than total IgE levels and a similar percentage of specific IgE (about 8%) was in the two strains.IgE antibodies were maximum at day 30 and day 60 after infection; however, a third peak at day 90 was observed only in Fischer rats. Some discrepancies between results obtained by PCA and immunosorbent techniques have been observed, which could be explained by differences in the affinity of IgE antibodies during infection or by the presence of total IgE in the PCA assay. There was a close parallelism between specific IgE antibodies levels and the course of immunity in Fischer rats. This parallelism supports the view that IgE could play a pre-eminent role in protective immunity in rat schistosomiasis.

Circulating antigens and immune complexes in Schistosoma mansoni-infected rats. Characterization by radioimmunoprecipitation-PEG assay (RIPEGA)

Circulating schistosome antigens (CSA) and circulating immune complexes (CLC) were investigated in rats infected with Schistosoma mansoni. The radioimmunoprecipitation-polyethylene glycol (PEG) assay (RIPEGA), with 125I-labelled anti-S. mansoni anti-serum, detected CSA during two distinct periods of the infection; the first between the 11th and the 14th week of infection and the second between the 11th and 14th week after infection. The CH50 deviation test revealed the presence of CIC in sera from infected rats, approximately at the two periods when CSA were detected. At 6 weeks of infection, the levels of CIC in infected rats were not different from those in control rats. However, a more sensitive method characterized IgG2a in C1q-binding C1C from infected rats. At weeks 5 and 6, IgE immune complexes were also detected in the serum from infected rats. In fact, the use of RIPEGA on the material eluted from infected rat serum after passage through an anti-IgE immunosorbent showed the presence of schistosome antigen at week 4, and at higher levels at week 6. Levels of 50% haemolytic complement in infected rat serum were lowered between the 2nd and the 4th week, the 5th and the 8th week and after the 12th week of infection. The possible role played by CIC in the protective mechanisms to a S. mansoni challenge infection in rats is discussed.