目的　观察脐血淋巴细胞低剂量辐射后体外抗K5 6 2细胞效应。方法　脐血淋巴细胞经不同低剂量辐射 ,辐射后不同时间 ,不同的细胞浓度与3H TdR标记的K5 6 2细胞混合培养 ,收获 ,测定每分钟放射性计数。用杀伤率和NK相对活性表示脐血淋巴细胞NK活性。用流式细胞仪测定其低剂量辐射后细胞表面免疫学标志变化。结果　脐血淋巴细胞经 2、5、10、2 0cGy辐射后NK活性明显增强 ,5cGy辐射后 2 4h ,NK活性增强最为明显。杀伤率和NK相对活性分别为 38.3 %和 172 .0 %。当效靶比 10∶1不变 ,效应细胞数达 5× 10 6后 ,增加效应细胞浓度并不能增加NK活性。经 5cGy低剂量辐射后 ,CD3、CD4、CD8、CD19、CD5 6表达增强。结论　脐血淋巴细胞在低剂量辐射下 ,可增强其CD3、CD4、CD8、CD19、CD5 6的表达 Objective To observe the anti-K562 cell effect in vitro after low-dose irradiation of umbilical cord blood lymphocytes. Methods Cord blood lymphocytes were irradiated with different doses of radiation. After irradiation, different concentrations of cells were mixed with 3H TdR-labeled K562 cells, harvested, and radioactivity counts were measured every minute. The NK activity of umbilical cord blood lymphocytes was expressed as the killing rate and NK relative activity. Flow cytometry was used to measure changes in cell surface immunological markers after low dose radiation. Results The NK activity of umbilical cord blood lymphocytes was significantly increased after 2, 5, 10, and 20 cGy irradiation, and the NK activity was most evident at 24 h after 5cGy radiation. The killing rate and NK relative activity were 38.3% and 172.0%, respectively. When the effective target ratio is 10:1 and the number of effector cells reaches 5×10 6 , increasing the concentration of effector cells does not increase NK activity. After low-dose irradiation at 5 cGy, the expression of CD3, CD4, CD8, CD19, and CD5 6 increased. Conclusion Umbilical cord blood lymphocytes can increase the expression of CD3, CD4, CD8, CD19 and CD5 6 under low dose radiation.