Abstract：To investigate activation characteristics and correlation with disease progression of nature regulatory T cells (nTregs) during Plasmodium berghei (P. berghei) ANKA infection, C57BL/6, BALB/c and DBA/2 mice were infected by intraperitoneal injection of 1×106 P. berghei ANKA parasitized erythrocytes. Parasitemia of individual mice was monitored by microscopic examination of blood smear stained with Giemsa. Spleen cell suspension was prepared from the mice sacrificed on day 0, 3, 5, 8 post infection (p.i.). The percentage of nTregs in spleen CD4+T cells was analyzed by flow cytometry quantitatively. Levels of IFN-γ and IL-10 in spleen supernatants were measured by ELISA kits and the concentration of NO was detected by Griess’s method. C57BL/6 mice died from 8 to 11 days after infection when parasitemia was 15-20% with cerebral malaria (CM), while BALB/c and DBA/2 mice survived until weeks 3 to 4 after infection and died of anemia and overwhelming parasitemia (70-80%). The percentage of nTregs in total spleen CD4+ T cell population started to elevate after infection and reached the peak on day 3 p.i. in CM-susceptible C57BL/6 mice or CM-resistant BALB/c and DBA/2 mice,and gradually reduced from day 5 p.i. to day 8 p.i.. On day 8 p.i., C57BL/6 mice showed the most significant decline in the percentage of nTregs. The percentage of nTregs in C57BL/6 mice was significantly lower than that in BALB/c and DBA/2 mice. IFN-γ, NO and IL-10 in cultured splenocyte supernatants began to increase after infection and reached the peak on day 5 p.i.. The results indicated that from day 5 p.i. to day 8 p.i., there were slight decline of IFN-γ and NO but significant decline of IL-10 in C57BL/6 mice. Moreover, there were significant decline of IFN-γ and NO but slight decline of IL-10 in BALB/c and DBA/2 mice. IFN-γ and NO in C57BL/6 mice were significantly higher than that in BALB/c and DBA/2 mice, while the level of IL-10 in C57BL/6 mice was lower than that in BALB/c and DBA/2 mice. The correlation analysis indicated that the percentage of nTregs was negatively associated with IFN-γ and NO, while the level of IL-10 was positively associated with parasitemia after infection. Results suggested that the dynamic changes of nTregs were closely associated with the infection outcome of host during P. berghei ANKA infection period.
〔1〕Randall LM,Amante FH,McSweeney KA,et al.Common strategies to prevent and modulate experi mental cerebral malaria in mouse strains with different susceptibilities〔J〕.Infect I m-mun,2008,76:3312-3320.
〔2〕Amante FH,Stanley AC,Randall LM,et al.Arole for natural regulatory T cells in the pathogenesis of experi mental cerebral malaria〔J〕.AmJ Pathol,2007,171:548-559.
〔3〕Weiser S,Miu J,Ball HJ,et al.Interferon-gamma synergises with tumour necrosis factor and lymphotoxin-alpha to enhance the mRNA and protein expression of adhesion molecules in mouse brain endothelial cells〔J〕.Cytokine,2007,37:84-91.
〔4〕Couper KN,Blount DG,Riley EM.IL-10:the master regulator of i mmunity toinfection〔J〕.J I mmunol,2008,180:57715777.
〔5〕Finney OC,Nwakanma D,Conway DJ,et al.Homeostatic regu-lation of Teffector to Treg ratios in an area of seasonal malaria transmission〔J〕.Eur J I mmunol,2009,39:1288-1300.
〔6〕Walther M,Jeffries D,Finney OC,et al.Distinct roles for FoXP3+and FOXP3-CD4+T cells in regulating cellular i mmunity to uncomplicated and severePlasmodium falciparummalaria〔J〕.PLoS Pathog,2009,5(4):e1000364.
〔7〕Jennings VM,Lal AA,Hunter RL.Evidence for multiple path-ologic and protective mechanisms of murine cerebral malaria〔J〕.Infect I mmun1998,66:5972-5979.
〔8〕Torcia MG,Santarlasci V,Cosmi L,et al.Functional deficit of Tregulatory cells in Fulani,an ethnic group with lowsuscepti-bility toPlasmodium falciparummalaria〔J〕.Proc Natl Acad Sci US A,2008,105:646-651.
〔9〕von Boehmer H.Mechanisms of suppression by suppressor T cells〔J〕.Nat I mmunol,2005,6:338-344.
〔10〕Thornton AM,Shevach EM.CD4+CD25+i mmunoregulatory Tcells suppress polyclonal T cell activation in vitro by inhibi-ting interleukin2production〔J〕.J Exp Med,1998,188:287-296.
〔11〕Vigrio AM,Gorgette O,Dujardin HC,et al.Regulatory CD+4CD2+5Foxp3+Tcells expand during experi mentalPlasmo-diuminfection but do not prevent cerebral malaria〔J〕.Int J Parasitol,2007,37:963-973.
〔12〕Wang QH,Liu YJ,Liu J,et al.Plasmodium yoelii:assess-ment of production and role of nitric oxide during the early sta-ges of infectionin susceptible and resistant mice〔J〕.Exp Parasi-tol,2009,121(3):268-273.
〔13〕Tongren JE,Yang C,Collins WE,et al.Expression of proin-flammatory cytokines in four regions of the brain inMacaque mulatta(rhesus)monkeys infected withPlasmodiumcoatneyi〔J〕.AmJ Trop Med Hyg,2000,62(4):530-534.
〔14〕Niikura M,Kamiya S,Nakane A,et al.IL-10plays a crucial role for the protection of experi mental cerebral malaria by co-in-fection with non-lethal malaria parasites〔J〕.Int J Parasitol,2010,40(1):101-108.
