Suppression of splenic natural killer cell activity in rats with brain tumors.

After inoculating 9L glioma cells into the brains or into subcutaneous regions of the back of rats, we investigated splenic natural killer (NK) cell activity for 3 weeks using a 4-hour 51Cr release assay. Only rats with brain tumors showed decreased splenic NK cell activity. The spleens of these rats were morphologically small and atrophic. Expansive brain tumors were compressing the basal ganglia, thalamus, and hypothalamus after 2 weeks, and the rats ultimately died of cerebral herniation, usually by 3 weeks after inoculation. The decreased splenic NK cell activity in rats with brain tumors might be the result of neuroimmunomodulation secondary to hypothalamic dysfunction due to increasing tumor compression.