Augmentation of NK cell activity by soluble and particulate fractions of Toxoplasma gondii

The ability of sonicates of Toxoplasma gondii and of subcellular fractions of the organism to enhance natural killer (NK) cell activity in mice was examined. Treatment of BALB/c mice with the sonicate preparations enhanced peritoneal and splenic NK activity to the level obtained with intact tachyzoites. Similar augmentation of NK activity in A/J, C57BL/6, and C3H/HeJ mice was also observed. Administration of Toxoplasma sonicate intraperitoneally, intravenously, or subcutaneously enhanced both peritoneal and splenic NK activity. Treatment of mice with a sonicate of L929 fibroblast failed to enhance their NK activity. Concentrations of sonicates ranging from 400 to 4 micrograms of protein enhanced both peritoneal and splenic NK activity. Both the soluble and particulate fractions of the sonicate obtained by differential centrifugation were capable of enhancing peritoneal NK activity, whereas splenic NK activity was enhanced only by the particulate fraction. Heat, protease, and sodium periodate treatment of the Toxoplasma sonicate completely abolished its capacity to augment NK activity. Gel filtration studies revealed that the NK augmenting activity of the Toxoplasma sonicate is distributed over a wide molecular weight range.