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

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 CD_4~+T 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 CD_4~+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 CD_4~+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 CD_4~+T h1 type cell responses in the early stage of primary infection than those in re-infection.