Mice chronically exposed to low dose ionizing radiation possess splenocytes with elevated levels of HSP70 mRNA, HSC70 and HSP72 and with an increased capacity to proliferate.

The purpose of this study was to determine whether the enhanced proliferative activity of splenocytes induced by exposing mice to whole body, chronic, intermittent low doses of ionizing radiation is associated with an increase in the expression of stress protein genes. Mice were exposed to a gamma-irradiation protocol of 0, 0.04 or 0.10 Gy/day for 5 consequent days/week, for 4 weeks. Splenocytes were then assessed for their levels of heat shock protein (HSP) 70 mRNA, glyceraldehyde 3-phosphate dehydrogenase (GAPD) mRNA, HSC70 (a constitutively-expressed isoform of HSP70) and HSP72 (an inducible isoform of HSP70), before and 1 day after mitogenic stimulation. Splenocytes from mice exposed to 0.04 Gy/exposure contained elevated constitutive levels of HSP70 mRNA, HSC70 and HSP72. These splenocytes responded to T, but not B, cell mitogens by further increasing their levels of HSP70 mRNA, HSC70 and HSP72 and by mounting a heightened proliferative response. However, an exposure of 0.10 Gy was ineffective. Thus, the constitutive levels of HSP70 mRNA, HSC70 and HSP72 and the mitogen-stimulated levels of HSC70 and HSP72 of splenocytes from mice exposed to 0.10 Gy/exposure were comparable with those of sham-irradiated mice. Moreover, their proliferative activity in response to mitogenic stimulation was also comparable with that of splenocytes from sham-irradiated mice.