Miller G K, Benjamin S A
Lab Invest. 1985 Feb;52(2):224-31.
Quantitative morphology of the canine fetal thymus was studied to evaluate the age-dependent radiosensitivity of the developing immune system. Pregnant beagle dams received abdominal 60Co gamma exposures (200 R) or were sham irradiated at one of three ages in gestation, 30, 40, or 45 days. The mean calculated dose to each fetus was 1.5 Gray. One-half of the fetuses in each litter were harvested by hysterotomy at 5 days and one-half at 10 days post-irradiation (PI). The volumes of the thymic lobules and lobular cortices were significantly reduced at 5 and 10 days PI when compared with age-matched controls. Thymic cortical volumes in irradiated fetuses were reduced between 13 and 29% from control volumes by 5 days PI and 8 and 13% by 10 day PI. Thymic medullary volumes in irradiated fetuses were reduced 18 to 23% by 5 days PI and 27 to 54% by 10 days PI. The reductions in medullary volumes in fetuses irradiated at 35, 40, and 45 days of gestation and evaluated at 10 days PI were 54, 38, and 27%, respectively. Although injury to both thymic cortices and medullas was greater following exposures earlier in gestation, damage to medullas was relatively more severe than in cortices following exposure at any one age. The degree of reduction of medullary volume reflects thymic epithelial injury and is surprising since thymic epithelium is considered to be radioresistant in the adult. Such injury may have serious consequences postnatally as normal differentiation of T cell subpopulations is dependent upon the integrity of the thymic microenvironment. Damage to the thymic microenvironment could result in defects in immunologic regulation and in immune deficiencies.
研究犬胎儿胸腺的定量形态学，以评估发育中免疫系统的年龄依赖性放射敏感性。怀孕的比格犬母犬在妊娠的三个年龄阶段之一，即30、40或45天，接受腹部60Coγ射线照射（200伦琴）或假照射。计算得出每个胎儿的平均剂量为1.5戈瑞。每窝胎儿的一半在照射后5天通过子宫切开术取出，另一半在照射后10天取出。与年龄匹配的对照组相比，照射后5天和10天胸腺小叶和小叶皮质的体积显著减小。照射后5天，照射胎儿的胸腺皮质体积比对照体积减少了13%至29%，照射后10天减少了8%至13%。照射胎儿的胸腺髓质体积在照射后5天减少了18%至23%，在照射后10天减少了27%至54%。在妊娠35、40和45天照射并在照射后10天评估的胎儿，其髓质体积的减少分别为54%、38%和27%。尽管在妊娠早期照射后胸腺皮质和髓质的损伤都更大，但在任何一个年龄照射后，髓质的损伤相对皮质更严重。髓质体积的减少程度反映了胸腺上皮的损伤，这令人惊讶，因为胸腺上皮在成体中被认为是抗辐射的。这种损伤在出生后可能会产生严重后果，因为T细胞亚群的正常分化依赖于胸腺微环境的完整性。胸腺微环境的损伤可能导致免疫调节缺陷和免疫缺陷。
