Analysis of Thymidine phosphorylase- Uridine phosphorylase double knockout mice

胸腺嘧啶磷酸化酶（TP）是一种参与胸腺嘧啶可逆转化为胸腺嘧啶的酶。在癌症患者和荷瘤动物中，血浆TP水平升高，其在各种实体瘤中的表达高于邻近非肿瘤组织。TP本身和胸苷的降解产物2-脱氧-d -核糖都具有趋化和血管生成活性，其血管生成活性需要TP的酶活性。TP主要在肿瘤浸润边缘表达，TP的表达与胃癌和结直肠癌的浸润程度有关。慢性炎症组织中TP表达也升高。据报道，TNF α和IFN γ可诱导TP的表达。为了证实TP的生理作用，我们培育了TP基因缺失小鼠（TPKO）。TPKO小鼠对单核增生李斯特菌感染的抵抗力增强。接种后3 d， TPKO组脾脏和肝脏细菌负荷降低约1 log。TPKO小鼠血浆中干扰素γ水平升高，IL-10水平降低。取感染小鼠的肝细胞和脾细胞进行培养。TPKO小鼠细胞条件培养基中IL-10水平明显低于野生型小鼠。IL-10是一种有效的抗炎细胞因子，可以降低肿瘤浸润淋巴细胞的功能，促进肿瘤生长。因此，我们试图测试TP在肿瘤逃离免疫系统中的作用。将年龄和性别匹配的小鼠（野生型和TP-/-型）腹腔注射1 × 10^6的EL-4细胞。EL-4细胞攻毒2周后，TPKO小鼠腹水体积的增加和EL-4细胞的生长明显低于野生型小鼠。因此，TP可能使肿瘤逃避免疫破坏，促进肿瘤生长。

Thymidine phosphorylase (TP) is an enzyme involved in the reversible conversion of thymidine to thymine. In cancer patients and tumor-bearing animals, plasma TP level is elevated, and its expression in various solid tumors is higher than in the adjacent non-neoplastic tissues. Both TP itself and the degradation product of thymidine, 2-deoxy-D-ribose, had chemotactic and angiogenic activities, and the enzymatic activity of TP was required for its angiogenic activity. TP was expressed mainly at the invasive edges of tumors and TP expression was associated with the extent of invasion of gastric and colorectal carcinoma.TP expression was also elevated in chronically inflamed tissues. TNF alpha and IFN gamma are reported to induce TP expression. To confirm the physiological role of TP, we generated mice deficient in TP gene (TPKO). TPKO mice showed an increased resistance to infection by Listeria monocytogenes. Splenic and hepatic bacterial loads 3 days after inoculation were decreased about 1 logs in TPKO. TPKO mice displays increase Interferon gamma level in plasma whereas less level of IL-10. The liver cells and spleen cells were obtained from infected mice, and cultured. The IL-10 levels in the conditioned media of the cells from TPKO mice were significantly less than those from wild-type mice. IL-10 is known to be a potent anti-inflammatory cytokine, and is suggested to reduce the function of tumor infiltrating lymphocytes and contributes the tumor growth. Therefore, we tried to test the role of TP in the escape of tumors from immune systems. Age and sex matched mice (wild-type and TP-/-) were injected i.p. with 1x10^6 of EL-4 cells. Two week after the challenge with EL-4 cells, the increase in volumes of ascites and the growth of EL-4 cells are significantly less in TPKO mice than in wild-type mice. Thus, TP may allow the escape of tumors from immune destruction and contribute the tumor growth.