Previous studies have shown that the human eosinophil is a major effector cell in the complement-independent, antibody-dependent killing of the invasive larval stage (schistosomulum) of Schistosoma mansoni in vitro (1, 2). Early studies were carried out with eosinophils from normal, noneosinophilic individuals. However, helminth infections, including schistosomiasis, are consistently associated with increased levels of eosinophils in the blood. Consequently, a formal comparison of the killing capacity of eosinophils from noneosinophilic and from moderately eosinophilic, helminth-infected patients was made, which showed that eosinophils from moderately eosinophilic individuals were markedly more active in killing schistosomula than were cells from noneosinophilic individuals (3). This suggested that eosinophilia may involve not only an increased number of eosinophils in the blood, but also an increased functional activity of the individual ceils.Since previous work had suggested that eosinophila is a thymus-dependent phenomenon (4, 5), possibly attributable to soluble mediators (6, 7), the present study was undertaken in an attempt to relate eosinophilia to enhanced eosinophil function, by testing the hypothesis that mononuclear ceils from eosinophilic individuals, whose own eosinophils show an increased killing capacity, might produce an activity that could stimulate normal eosinophils and increase their cytotoxic potential. A brief description of our preliminary findings has previously been published (8). Materials and MethodsMedia and Reagents. The following media and reagents .were used in these experiments: MEM: I Eagle's Minimal Essential Medium (Flow Laboratories), containing 20 mM Hepes, 100 U/ml penicillin, 100/tg/ml streptomycin, and 30 mg/1 DNase, pH 7.3. MEM/FCS: MEM supplemented with 10% fetal calf serum (FCS) (Seralab), heat-inactivated at 56°C for 1 h. PBS: Phosphate-buffered saline, pH 7.3. PBS azide was supplemented with 0.1% sodium azide. Con A: Concanavalin A (Type IV, Sigma Chemical Co.) prepared as a stock solution at 1 mg/ ml in MEM and used at 10/tg/ml in either MEM or MEM/FCS. Emetine dihydrochloride

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A protein (eosinophil-activating factor, EAF), which enhances the capacity of human peripheral blood eosinophils to kill antibody-coated schistosomula of Schistosoma mansoni, has been partially purified from supernatants of cultured peripheral blood mononuclear cells by sequential chromatography on Sephacryl S200 and DEAE-cellulose. This protein is acidic with a molecular mass on gel filtration of 40 +/- 7 kDa. It not only enhances the activity of eosinophils against schistosomula but also increases their ability to lyse antibody-coated, herpes simplex virus-infected Chang liver cells. It enhances the production of superoxide and hydrogen peroxide by eosinophils that occurs both spontaneously and in response to opsonized zymosan. However, increased respiratory burst activity does not appear to be responsible for the enhancement of eosinophil-mediated killing of schistosomula, since a comparable or greater increase in hydrogen peroxide production is induced by column fractions that have little or no effect on schistosomulum killing. EAF enhances eosinophil degranulation, both spontaneously and after incubation with opsonized zymosan. Enhanced degranulation is associated with release of eosinophil peroxidase and eosinophil cationic protein. These findings suggest that EAF enhances the capacity of eosinophils to kill parasites by increasing the extent of eosinophil degranulation and the amount of toxic granule proteins that are secreted.

T cell lines and T cell clones derived from inbred Fischer rats and specific for Schistosoma mansoni antigens were established. Cell-free supernatants from the T cell lines demonstrated a marked capacity to enhance IgE- and IgG2a-dependent eosinophil-mediated killing of S. mansoni larvae in vitro. In addition, supernatants from cloned T cells stimulated with concanavalin A or specific antigen, or unstimulated, enhanced IgE-dependent eosinophil-mediated helminthotoxicity. The enhancing activity in both cases was very heat-stable (100 degrees C, 10 min). We also found that clone-derived supernatants enhance eosinophil peroxidase release upon stimulation with homologous IgE and anti-IgE as well as inducing a more delayed spontaneous release of peroxidase. In view of the established thymus dependency for the development of immunity to schistosomiasis in the rat, the availability of these S. mansoni-specific cloned T cells has enabled the relationship between eosinophils, lymphocytes and anaphylactic antibodies to be examined more closely.