Raji细胞逃逸NK细胞免疫杀伤机制的初步探讨

Aberrant expression of NKG2D ligands and high expression HLA-Ⅰmolecules may contribute to immune escape of Raji cells from NK cell-mediated immune surveillance of malignant lymphoma

目的探讨人B细胞淋巴瘤Raji细胞逃逸NK细胞免疫杀伤的机制。方法以K562细胞作为对照，应用LDH释放法检测不同效靶比时同种异体NK细胞杀伤Rail细胞的活性。并分别用PCR方法和流式细胞仪检测K562和Raji细胞MICA／B、ULBP1～3、HLA基因型和分子的表达情况。效靶比20：1时用单抗分别阻断K562和Raji细胞表面MICA、MICB、ULBP1、ULBP2、ULBP3和HLA-Ⅰ类分子，观察NK细胞对其杀伤活性的变化。结果不同效靶比时NK细胞杀伤Raji细胞的活性明显低于杀伤K562细胞的活性，二者之间差异有统计学意义（P〈0．05）。K562细胞表达MICA／B和ULBP1～3基因和分子，不表达HLA—Ⅰ类分子，Raji细胞表达ULBP1～3基因和HLA-Ⅰ类分子，不表达MICA／B和ULBP1～3分子。Rail细胞HLA基因型为A＊3、3，B＊71、71，Cw3、4。用单抗封闭MICA／B和ULBP1-3分子后，NK细胞对K562细胞的杀伤活性明显降低，对Raji细胞的杀伤活性无明显改变。结论Raji细胞逃逸NK细胞免疫杀伤机制和Raji细胞高表达HLA-Ⅰ类分子，不表达NKG2D的配体MICA／B和ULBP1～3有关。

Objective To explore the mechanism of immune escape of Raji cells from natural killer （NK） cell-mediated immune surveillance of B cell malignant lymphoma. Methods Taking K562-cell as positive control, cytotoxicities of NK cells isolated from 5 healthy vol- unteers against Raji cells were analyzed by LDH releasing assay at different effector-to-target cell （E：T） ratios. The genes and proteins expression of NKG2D ligands on K562 and Raji cell were measured by RT-PCR and flow cytometry, respectively. The genes of HLA- Ⅰ molecules in Raji cell and KIR of NK cell were assayed by PCR-SSCP. In blocking experiments, monoclonal antibodies of HLA- Ⅰ molecule and different NKG2D ligands were added to the target cell at E： T of 20： 1. Results Comparing with K562 cells, the Raji cells resisted NK cell cytolysis. The mRNA genes of ULBP1 - 3 were positive in two tumor cell lines. The mRNA genes of MICA/B was found in K562 cells, not in Raji cells. The HLA- class Ⅰ genotypes of Raji cells were A ＊ 3, 3; B ＊ 71, 71; Cw3, 4. The protein of MICA/B and ULBP1 - 3 were expressed on K562 cell line, but not on Raji cell line; HLA- Ⅰ molecule was found on the surface of Raji cell, but not on K562 cell. In blocking experim- ents, the cytotoxicity of NK cells against K562 cell was partially inhibited but that against Raji cell was not influenced when mAbs of different NKG2D ligands were added; the cytotoxicity of NK cells against Raji cell was obviously improved but that against K562 cell was not influenced when mAb of HLA- Ⅰ molecules was added. Conclusion Aberrant expression of NKG2D ligands and high expression HLA- Ⅰ molecules may contribute to immune escape of Raji cells from natural killer cell-mediated immune surveillance of B cell malignant lymphoma.