CD_4^+T细胞在约氏疟原虫抵抗型小鼠模型中的作用与地位

Function of CD_4^+T cells in the resistant type of mouse model infected with Plasmodium yoelii

目的探讨抵抗型小鼠CD4+T细胞在疟原虫感染过程中的作用与地位。方法以约氏疟原虫感染DBA/2小鼠,于自愈后30 d、60 d和90 d,分别用同种疟原虫进行再次感染。以吉姆萨薄血膜染色法观察小鼠虫体血症水平,采用ELISA法和Griess反应分别检测初次及再感染后第3 d和第10 d脾细胞培养上清中IFN-γ、NO水平和血清中特异性IgG水平,并以流式细胞仪检测小鼠脾细胞中CD4+T细胞百分率。结果初次感染后第3 d,疟原虫感染的红细胞出现于小鼠的外周血中,且其脾细胞可产生高水平的IFN-γ和NO;感染后10 d,IFN-γ和NO回落至感染前水平,CD4+T细胞百分率有所下降,但特异性IgG出现了有意义的升高。与初次感染相比,再感染过程中仅出现一过性低水平的虫体血症,再感染后第3 d和第10d的CD4+T细胞百分率和IFN-γ及NO水平均未出现有意义的变化,而高水平IgG一直持续存在。结论与再次感染相比,约氏疟原虫感染的抵抗型小鼠在初次感染早期可建立更为显著的CD4+Th1型细胞反应。

DBA12 mice infected with Plasmodium yoelii were re-infected intraperitoneally with the same parasite 17XL strain after recovery from the primary infection. The level of parasitemia in the infected mice was examined with Giemsa staining of the thin blood smears, and the levels of IFN-γ, and NO in the culture supernatants of spleen cells and the serum level of specific IgG on the 3 rd and 10 th day after primary and re-infection were determined by ELISA and Griess reaction respectively. Meanwhile, flow cytometry was used to analyze the percentage of CD4^＋ T cells in splenic cells of mice. Red blood corpuscle parastized with Plasmodia could be found in the peripheral blood of mice on the 3 rd day after primary infection, and high levels of IFN-γ and NO were detected in splenic cells , but they were dropped to the original levels on the 10 th day of infection. The percentage of CD4^＋ T cells was significantly reduced, but the level of specific IgG rose up obviously. All the mice from re-infected group showed lower level and shorter lasting parasitemia in comparison with those from primarily infected group. On the 3 rd or 10 th day after reinfection, the levels of IFN-γ, NO and percentage of CD4^＋ T cells were all just the same as those of the un-infected mice, but high level of IgG still persisted. These results indicate that mice resistant to infection with P. yoelii 17XL strain initiate stronger CD4^＋ Th1 type cell responses in the early stage of primary infection than those in re-infection.