Toxoplasmacidal activity of obioactin derived from hydrolyzed toxoplasma immune bovine serum in heterologous cell cultures

Serum samples were collected from Toxoplasma-infected cattle after challenge and 24 h after Toxoplasma lysate injection. They were hydrolyzed with proteinase, HCl and NaOH. Then substances 3,000 to 5,000 in molecular weight were obtained from fractionation by chromatography. Native serum was collected from cattle immune only to Toxoplasma was affected in homologous bovine monocytes. Of the hydrolyzed fractions, one termed Obioactin inhibited the growth of Toxoplasma in heterologous cells, such as mouse macrophages and kidney cells, canine monocytes, and human heart and brain cells. Its toxoplasmacidal activity was presumed to be derived from its non-specific cell potentiating effects. In mice immunized to Toxoplasma peritoneal macrophages released about 10 times as much superoxide (O₂⁻) and hydrogen peroxide (H₂O₂) as glycogen-elicited macrophages in normal mice. The release of O₂⁻ and H₂O₂ from glycogen-elicited and resident macrophages in normal mice showed a tendency to increase up to 72 h of incubation with 0.5% Obioactin. No changes in the O₂⁻ and H₂O₂ release were found in kidney cells during the period of incubation with Obioactin. In those immunized mice activated macrophages and kidney cells inhibited the intracellular multiplication of Toxoplasma parasites remarkably. It was suggested that the increase in O₂⁻ and H₂O₂ generating activity in the macrophages might be associated with the enhancement of antitoxoplasmatic activity. The mechanism of inhibition of Obioactin, however, might be different from that of mouse macrophages on the multiplication of Toxoplasma in mouse kidney cells.