A modified colorimetric method for the measurement of phagocytosis and antibody-dependent cell cytotoxicity using 2,7-diaminofluorene.

A sensitive and rapid colorimetric method for the in vitro determination of phagocytic activity and antibody-dependent cell-mediated cytotoxicity (ADCC) is described. The assay uses red blood cells (RBC) as target cells and relies on the specific oxidation of 2,7-diaminofluorene (DAF) by the pseudoperoxidase activity of hemoglobin (Hb). Generation of fluorene blue (FB), the chromophore formed upon oxidation of DAF, was a linear function of erythrocyte concentration. The oxidation of DAF by peritoneal macrophages (M phi) containing myeloperoxidase was negligible, confirming that the development of color was exclusively due to the pseudoperoxidase activity of Hb. A positive correlation was observed between FB formation and increased phagocytosis of opsonized erythrocytes. Phagocytosis increased as a function of time, reaching a maximum at 90 min of incubation. The phagocytosis of IgG-opsonized erythrocytes was greater than non-opsonized erythrocytes and was inhibited by high concentrations of non-specific human or mouse IgG, showing that phagocytosis was mediated by the Fc gamma receptor of macrophages. The interaction between opsonized RBC and macrophages also evoked an antibody-dependent extracellular lysis, however this process was slower than ingestion. The DAF phagocytosis assay has shown to be very sensitive, simple, rapid and safe.

Resistance to reinfection in experimental murine schistosomiasis: role of porto-hepatic hemodynamics.

Experiments were conducted to evaluate critically, and independently of the immune system, the possible role of hemodynamic mechanisms in resistance to schistosomal reinfection. The effects of a challenge schistosomal infection were compared in groups of mice which were either previously infected with schistosomiasis, vaccinated with irradiated cercariae, or underwent partial portal vein ligation for the induction of portal hypertension and porto-systemic shunting. Following infection with 60 cercariae, the appearance of portal hypertension preceded by approximately 2 weeks the development of porto-systemic shunting, which reached maximal values 11 weeks postinfection. Such a primary infection conferred on C3H mice an estimated 90% protection to a 2nd infection, measured by the reduction of worm burden. Worm burdens were also reduced in vaccinated and ligated animals as compared to normal controls. The protection amounted to 30% and 56%, respectively, in the C3H strain and 63% and 75-85%, respectively, in the C57Bl/6 strain. Reduction in worm burden in the ligated animals is believed to be due to the extrahepatic porto-systemic vascular shunts. Hemodynamic as well as immunological factors may account for the resistance to reinfection observed in chronic murine schistosomiasis.

Schistosoma mansoni: the basis for the antischistosomal effect of cyclosporine A.

A potent antiparasitic effect against a broad range of microorganisms is now known to follow the administration of cyclosporine A (CSA) to a variety of mammalian species and birds. Even though in the case of Schistosoma mansoni a direct antischistosomal effect by CSA has been in principle ruled out, this possible mechanism of action has not been previously explored in depth. In this paper we show that (a) concentrations of CSA of as low as 1 microgram/ml are schistosomulicidal in vitro as determined by morphological criteria, (b) mice receiving antischistosomal regimens in vivo exhibit serum concentrations of CSA that are within the range of toxic doses in vitro, (c) schistosomulicidal concentrations of CSA are maintained in vivo for sufficiently long periods of time to secure parasite death, (d) the antischistosomal activity of heat-inactivated mouse sera closely correlates with their levels of CSA, and (e) independent of the site of administration, CSA offers protection against a schistosomal infection in vivo only when present in the serum. The data strongly support the contention that CSA has a direct effect on the early forms of Schistosoma mansoni, and suggest that interference with a survival mechanism, perhaps common to several parasites, represents one likely mode of action.

Interaction of iron polymers with blood mononuclear cells and its detection with the Prussian Blue reaction.

An inhibitory effect of iron salts on various immune functions in vitro has been reported in several laboratories during the last few years. This study confirms and extends those observations by showing that iron citrate inhibits the mitogen-induced (PHA, Con A and PWM) lymphocyte proliferation. Such inhibition is observed in the presence of ferric citrate with a metal-to-ligand molar ratio of 1:1 but not with ferric citrate with metal-to-ligand molar ratio 1:20 in which the formation of polynuclear iron complexes is prevented. Increasing the concentration of serum in the culture medium diminished the inhibitory effect of 1:1 ferric citrate. Using the Prussian Blue reaction the presence of ferric iron was observed on the cell surface. It is proposed that the deposition of polynuclear iron complexes on the lymphocytes membrane is one of the possible factors determining the iron inhibitory effect.