目的　研究乳腺癌细胞表面MHCⅡ类抗原与共刺激分子CD4 0、CD80 (B7 1)和CD86 (B7 2 )的表达。方法　采用流式细胞技术检测 5株乳腺癌细胞MCF 7、SK BR 3、T4 7D、MDA MB 4 35s和ZR 75 30表面MHCⅡ类抗原与共刺激分子CD4 0、CD80 (B7 1)和CD86 (B7 2 )的表达 ,并与正常乳腺细胞HBL 10 0作比较。结果　 5株乳腺癌细胞MHCⅡ类分子表达均与正常乳腺细胞HBL 10 0差异有显著性 (P <0 .0 5 ) ,MCF 7细胞表达水平最低 ,约为HBL 10 0的 1/ 5。MDA MB 4 35s与ZR 75 30细胞表达水平为HBL 10 0的 2倍 ,MDA MB 4 35s荧光强度也比HBL 10 0及其他乳腺癌细胞高 ,但MDA MB 4 35s细胞表面CD4 0分子表达水平最低 ,约为MCF 7与HBL 10 0CD4 0分子表达水平的 10 %。MDA MB 4 35s细胞的CD80和CD86分子表达水平与HBL 10 0相当 (P >0 .0 5 ) ,另 4株乳腺癌细胞的CD80和CD86分子表达均比HBL 10 0低 (P <0 .0 5 )。结论　乳腺癌细胞表面MHCⅡ与共刺激分子表达异常 ,不同细胞表面分子的表达有所差异。乳腺癌细胞可通过这些分子表达异常而发生免疫逃逸 Objective To study the expression of MHC class II antigens and costimulatory molecules CD4 0, CD80 (B7 1) and CD86 (B7 2) on the surface of breast cancer cells. Methods Flow cytometry was used to detect the expression of MHC class Ⅱ antigens on costimulatory molecules CD4 0, CD80 (B7 1) and CD86 (B7 2) on 5 breast cancer cell lines MCF 7, SK BR 3, T4 7D, MDA MB 4 35s and ZR 75 30 ), And compared with normal breast cell HBL10. Results The expression of MHC class II molecules in 5 breast cancer cells was significantly different from that in normal breast cells (P <0.05). The expression level of MCF 7 cells was the lowest, about 1/5 of HBL 10 0. The MDA MB 4 35s and ZR 75 30 cells expressed twice as much as HBL 10 0, and the fluorescence intensity of MDA MB 4 35s was also higher than those of HBL 10 0 and other breast cancer cells, but the lowest expression level of CD4 0 on MDA MB 4 35s cells , About 10% of the expression level of MCF7 and HBL10 0CD40 molecules. The expression of CD80 and CD86 in MDA MB4 35s cells was comparable to that in HBL10 (P> 0.05), while the expression of CD80 and CD86 in the other 4 breast cancer cells was lower than that in HBL10 (P <0. 0) 5). Conclusion The expression of MHC Ⅱ and costimulatory molecules on breast cancer cells is abnormal, and the expression of different cell surface molecules is different. Breast cancer cells can escape immune escape through aberrant expression of these molecules