Inhibition of mitogen- and antigen-induced lymphocyte activation by human leukemia cell gangliosides.

Human leukemia cell gangliosides were found to inhibit in vitro activation of human lymphocytes by lectins and the soluble antigen Candida albicans at concentrations as low as 2 micrograms/2 X 10(5) lymphocytes/0.2-ml cultures. The inhibition was not due to a reduction in the number of viable cells, but to an inhibition of blast formation. Three gangliosides were purified from the original mixture and tested for their ability to inhibit in vitro activation of lymphocytes. All 3 gangliosides inhibited lymphocyte activation to a similar degree when tested over a concentration range of 5 to 100 micrograms per ml of culture. Removal of sialic acid from the gangliosides by neuraminidase treatment significantly reduced or abolished their inhibitory effect. The gangliosides used in our analyses are not unique to leukemia cells. However, their concentration is increased in patients with cancers. Therefore, our results demonstrate that gangliosides isolated from human leukemia cells can inhibit lymphocyte activation when added in concentrations equivalent to those found in sera of patients with leukemia and other cancers.