Influence of CD4~+CD25~+ regulatory T cells on the course and outcome of infection with rodent plasmodium

To investigate the dynamic changes of CD4+CD25+ regulatory T cells in a mixed infection of mouse with Plasmodium yoelii and Plasmodium chabaudi,DBA/2 and BALB/c mice were injected intra-peritoneally with the parasitized erythrocytes using the lethal type of P.yoelii(P.y17XL) and P.chabaudi(P.cAS) as well as the mixed infection of P.y17XL plus P.cAS(1∶1).Then,the radio of the infected RBC was countered and the numbers of CD4+CD25+ regulatory T cells in spenocytes were detected dynamically by flow cytometry.It was found that DBA mice with mixed infection spontaneously cured 18 days after infection,while in BALB/c mice,although death occurred at 8 days after infection,moreover,in comparison with mice infected with P.y17XL(death occurred at 5 says after infection),the time of death was obviously delayed.The numbers of CD4+CD25+ regulatory T cells of DBA mice infected with P.y17XL and P.y17XL plus P.cAS approached their peaks at 5 days after infection and then declined gradually,meanwhile,those of mice infected with P.cAS reached its peak on 10 days post-infection,exhibited 3 times and 2 times higher in numbers in comparison with those of the other infected mice at the same day and all the mice died.Howover,the numbers of CD4+CD25+ regulatory T cells in BALB/c infected with P.y17XL and P.y17XL plus P.cAS appeared significant increase,approaching up to 30% of the total CD4+ T cells on 5 and 8 days post-infection(P0.01).Those of BALB/c mice infected with P.cAS increased slowly approaching to 14% of the total CD4+ T cells on 5 days post-infection.From these observations,it is evident that the abonormal rise in the number of CD4+CD25+ regulatory T cells in infection with plasmodium may be related to the outcome of infection.