增强型金黄色葡萄球菌肠毒素C2突变体及其超抗原活性

Enhanced SEC2 mutants and their superantigen activities

摘要:

金黄色葡萄球菌肠毒素C2 (Staphylococcal enterotoxin C2，SEC2) 作为一种超级抗原蛋白，极微量即可有效激活机体免疫系统，这一特性可应用于对肿瘤和感染性疾病的辅助治疗。为了增强SEC2的超抗原活性，应用over-lap PCR方法将SEC2中的102~106位GKVTG氨基酸残基分别突变为WWH、WWT和WWP，获得3种突变体ST-1、ST-2和ST-3。三种突变体刺激小鼠淋巴细胞增殖活性和肿瘤细胞生长抑制活性与野生型SEC2相比均有显著提高。ST-1和ST-3的致热活性与野生型SEC2相当，而ST-2的致热活性明显高于野生型SEC2。此外，三种突变体体外刺激淋巴细胞分泌IL-2、IFN-γ和TNF-α的水平也显著提高，这可能是导致突变体具有较高肿瘤细胞生长抑制活性的原因。进一步实验发现，三种突变体刺激下，小鼠脾淋巴细胞mVβ8.2基因的转录水平较野生型SEC2显著增加，暗示突变体对TCR mVβ8.2分子亲和力的提高，可能是其超抗原活性增强的主要原因。

Abstract:

As a superantigen protein, Staphylococcal enterotoxin C2 (SEC2) activates the immune system effectively even in extremely low concentrations, and this property could be applied in adjuvant therapy against tumors and infectious diseases. In order to enhance the superantigen activity of SEC2, the residues at position 102?106 of native SEC2 were substituted for WWH, WWT and WWP by over-lap PCR, and three mutants named ST-1, ST-2 and ST-3 were obtained. Stimulating activity to murine lymphocytes proliferation and inhibiting activity to tumor cell growth of the three mutants were significantly improved compared with the native SEC2. Febrile activities of ST-1 and ST-3 were comparable with the native SEC2, but ST-2 showed markedly increased febrile activity than native SEC2. Moreover, the levels of IL-2, IFN-γ and TNF-α secreted by T cells stimulated with the three mutants were significantly improved, which might be the possible reason for enhanced tumor cell growth inhibition activities. Furthermore, mVβ8.2 gene transcription levels of murine splenocytes stimulated by the three mutants were dramatically increased compared with native SEC2, suggesting their increased affinities to TCR mVβ8.2 molecular, which might be the main reason for their enhanced superantigen activities.