Abstract: Objective  To investigate the effect of L-arginine （L-Arg） during blood-stage infection by P.y17XL in DBA/2 mice. Methods  DBA/2 mice were divided into 2 groups， 20 mice in each group. Mice were respectively administered with L-Arg (1.5 g/kg, L-Arg group) and normal saline (control group) 7 days before they were infected intraperitoneally by 1×106 pRBC. Parasitemia were detected by Giemsa stained thin-smear microscopy and survival rate were monitored daily. Flow cytometry was introduced to detect the subsets of splenic CD4+CD69+T cells, F4/80+CD36+ macrophages, myeloid dendritic cells(mDCs) (CD11c+CD11b+), plasmacytoid dendritic cells (pDCs) (CD11c+B220+) on day 3, 5 post infection (p.i.). The levels of IFN-γ and NO in the supernatant of splenocytes culture were detected by ELISA and Griess reaction, respectively.  Results   Pretreatment of mice with L-Arg significantly decreased the parasitemia from 45% to 20% and shortened selfcure time from 22 d to 20 d after infection. The level of F4/80+CD36+ macrophages [(29.61±0.47)%], IFN-γ [(485.84±39.31) pg/ml], CD4+CD69+ T cells [(7.3±0.68)%],  NO [(42.51±1.32)  μmol/L], mDCs(CD11c+CD11b+) [(5.51±0.87)%] and pDCs(CD11c+B220+) [(5.60±0.85)%] in L-Arg group was higher than those in control group [(36.46±1.33)%,  (767.86±20.56) pg/ml, （11.27±0.97）%,  (78.66±2.89) μmol/L, (10.02±0.37)%] and (9.01±0.53)%, respectively].  Conclusion  L-Arg enhances Th1 immune responses during the early stage of P.y17XL infection in DBA/2 mice via the activation of DCs.

Key words:  , L-Arginine；Plasmodium yoelii 17XL；Immunoregulation；Th1 immune response；Dendritic cell