Low-level exposures to ionising radiation modulate the anti-tumour activity of murine NK cells

Experimental evidence from the recent years indicates that low-level irradiations with X- or gamma rays may inhibit development of both primary and secondary tumours and stimulate the activity of natural anti-tumour immune mechanisms. Natural killer (NK) cells play an important role in anti-tumour defence of the host. In the present investigation cytotoxic activity, production of interferon-ă, and expression of the Fas ligand (FasL) were estimated in the NK splenocytes collected from BALB/c mice whose whole body was pre-exposed to irradiation with 0.1, 0.2, or 1.0 Gy X-rays. The results indicate that cytotoxic activity of the irradiated NK cells was significantly stimulated compared to that of the NK effectors obtained from the sham-exposed mice. This effect was totally abrogated by injection of the anti-asialo GM1 antibody. In addition, compared to the control mice, NK cells obtained from the irradiated animals exhibited reduced surface expression of FasL. Collectively, the obtained results suggest that the inhibitory effect of the low-level irradiations with X-rays on the development of pulmonary tumour nodules may be directly associated with stimulation by such exposures of anti-neoplastic functions mediated by NK cells.