Radiation injury of the developing immune system in the beagle dog

Fetal lymphoid organs of the beagle dog were studied to determine if the developing immune system displays an age-dependent sensitivity to ionizing radiation. Pregnant beagle dams received abdominal 60Co gamma exposures to 200R or were sham irradiated at one of three ages in gestation; 35, 40, or 45 days postcoitus. The mean calculated dose to each fetus was 1.5 Gy. Half the fetuses in each litter were harvested by hysterotomy at five days and half at ten days postirradiation (PI). The volumes of the thymus lobules and lobular cortices were significantly reduced at five and ten days PI as compared to age matched controls. Radiation damage in the developing immune system was expressed in the lymphocyte populations of fetal lymphoid organs and in thymus epithelium. Damage was qualitatively and quantitatively more severe following irradiation earlier in gestation, confirming that the developing immune system displays an age-dependent sensitivity. Prenatal radiation injury to the developing lymphoid system could compromise postnatal immunologic function and could alter immunoregulation