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Long term effects of adult-thymectomy on natural killer activity and spontaneous tumor incidence.

Long term effects of adult-thymectomy on both natural killer (NK) activity and spontaneous tumor incidence were investigated in C57BL/6 mice maintained in specific pathogen free atmosphere. As compared with the age matched sham-thymectomized mice, a substantially low incidence of spontaneous tumour (6%) and a high level of splenic NK activity were noted one and a half year later in C57BL/6 mice thymectomized at 6 weeks of age. In contrast, sham-thymectomized mice showed a high incidence of the spontaneous tumor (57%) associated with a low level of splenic NK activity. These results suggest that NK cells play a critical role to prevent the occurrence of spontaneous tumor in vivo.