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Background Emerging data has suggested that Tregs, Th17, Th1 and Th2 are correlated with early immune mechanisms by controlling Plasmodium infection. Plasmodium infection appeared to impair the antigen presentation and maturation of DCs, leading to attenuation of specific cellular immune response ultimately. Hence, in this study, we aim to evaluate the relevance between DCs and Tregs/Th17 populations in the process and outcomes of infection with Plasmodium yoelii 17XL (P.y 17XL). Methods DCs detection/analysis dynamically was performed by Tregs depletion or Th17 neutralization in P.y 17XL infected BALB/c mice via flow cytometry. Then the levels of cytokines production were detected using enzyme-linked mmunosorbent assay (ELISA). Results Our results indicated that Tregs depletion or Th17 neutralization in BALB/c mice infected with P. y17XL significantly up-regulated the percentages of mDC and pDC, increased the expressions of major histocompatibility complex (MHC) class II, CD80, CD86 on DCs and the levels of IL-10/IL-12 secreted by DCs, indicating that abnormal amplification of Tregs or Th17 may damage the maturation and function of DCs during the early stage of malaria infection. Interestingly, we also found that the abnormal amplification of Th17, as well as Tregs, could inhibit the maturation of DCs. Conclusions Tregs skewing or Th17 amplification during the early stage of malaria infection may inhibit the maturation and function of DCs by modifying the subsets of DCs, expressions of surface molecules on DCs and secretion mode of cytokines.

Backgroud It is important to expound the opposite clinical outcomes between children and adulthood for eradicate malaria. There remains unknown about the correlation between adaptive immune response and age-related in malaria. Methods 4 and 8-week-old mice were used to mimic children and adulthood, respectively. Parasitemia and the survival rate were monitored. The proportion and function of Th1 and Th2 cells were detected by FACS. The levels of IFN-γ, IL-4, total IgG, IgG1, IgG2a and Plasmodium yoelii MSP-1-specific IgG were measured by ELISA. Results The adult group showed greater resistance to P. yoelii 17XL infection, with lower parasitemia. Compared with 4-week-old mice, the percentage of CD4 + T-bet + IFN-γ + Th1 cells as well as IFN-γ production were significantly increased on day 5 p.i. in the 8-week-old mice after P. yoelii 17XNL infection. The percentage of CD4 + GATA3 + IL-4 + Th2 cells and CD4 + CXCR5 + Tfh cells, and IL-4 production in the 8-week-old mice significantly increased on day 5 and day 10 after P. yoelii 17XNL infection. Notably, the levels of total IgG, IgG1, IgG2a and P. yoelii MSP-1-specific IgG were also significantly increased in the 8-week-old mice. PD-1, a marker of exhaustion, was up-regulated on CD4 + or activated CD4 + T cells in the 8-week-old mice as compared to the 4-week-old group. Conclusions Thus, we consider that enhanced cellular and humoral adaptive immunity might contribute to rapid clearance of malaria among adults, likely in a PD-1-dependent manner due to induction of CD4 + T cells exhaustion in P. yoelii 17XNL infected 8-week-old mice.

Background Clinical immunity to malaria in human populations is developed after repeated exposure to malaria. Regulation and balance of host immune responses may lead to optimal immunity against malaria parasite infection. Polysaccharides (ABPS) derived from the Chinese herb ox knee Achyranthes bidentata possess immuno-modulatory functions. The aim of this study is to use the rodent malaria model Plasmodium yoelii 17XL ( P. y 17XL) to examine whether pretreatment with ABPS will modulate host immunity against malaria infection and improve the outcome of the disease. Methods To determine whether ABPS could modulate immunity against malaria, mice were pretreated with ABPS prior to blood-stage infection by P. y 17XL. Host survival and parasitaemia were monitored daily. The effect of pretreatment on host immune responses was studied through the quantitation of cytokines, dendritic cell populations, and natural regulatory T cells (Treg). Results Pretreatment with ABPS prior to infection significantly extended the survival time of mice after P. y 17XL infection. At three and five days post-infection, ABPS pretreated mice developed stronger Th1 immune responses against malaria infection with the number of F4/80 + CD36 + macrophages and levels of IFN-γ, TNF-α and nitric oxide being significantly higher than in the control group. More importantly, ABPS-treated mice developed more myeloid (CD11c + CD11b + ) and plasmacytoid dendritic cells (CD11c + CD45R + /B220 + ) than control mice. ABPS pretreatment also resulted in modulated expression of MHC-II, CD86, and especially Toll-like receptor 9 by CD11c + dendritic cells. In comparison, pretreatment with ABPS did not alter the number of natural Treg or the production of the anti-inflammatory cytokine IL-10. Conclusion Pretreatment with the immuno-modulatory ABPS selectively enhanced Th1 immune responses to control the proliferation of malaria parasites, and prolonged the survival of mice during subsequent malaria infection.

The outcome of Plasmodium yoelii 17XL-infected BALB/c and DBA/2 mice, ranging from death to spontaneous cure, respectively, depends largely on the establishment of effective pro-inflammatory type 1 responses during the early stages of infection and associates with CD4+CD25+Foxp3+regulatory T cells (Tregs). Here, effects of Tregs were analysed on early P. yoelii 17XL infection in BALB/c and DBA/2 mice. In vivo depletion of Tregs significantly reversed the inhibited establishment of effective pro-inflammatory type 1 responses in BALB/c mice, indicating that this cell population contributed to the suppression of T-cell function in malaria. Moreover, the proportion and absolute numbers of IL-10-secreting Tregs in BALB/c mice were significantly higher than that found in DBA/2 mice by intracytoplasmic staining, and IL-10 production was correlated with the Tregs population. In addition, in vivo Tregs depletion decreased the production of IL-10 and the apoptosis of CD4+ T cells. Consistently, IL-10R blockade also had the same effect as that of Tregs depletion in P. yoelii 17XL-infected BALB/c mice. Our data demonstrate that Tregs perhaps have an important role in regulating pro-inflammatory type 1 responses in an IL-10-dependent manner and induce CD4+ T cell apoptosis during the early stage of P. yoelii 17XL infection.

Macrophage migration inhibitory factor (MIF) is a cytokine recognized regulator of the inflammatory immune response associated with several immune cells that produce inflammatory cytokines such as IL-1β, IL-6, IL-12, IL-18, and TNF-α. This study aimed to understand the effect of MIF on the immune response and pathogenesis during Plasmodium infection. Wild-type (Wt) and MIF knockout ( Mif -/- ) mice were intravenously infected with 1×10 3 Plasmodium yoelii ( Py ) 17XL-parasitized red blood cells. Our data showed that Py 17XL-infected Wt mice died 11 days postinfection, while Mif -/- mice showed reduced parasitemia and an increase in their survival at day 11 up to 58%, importantly they succumb up to day 21 postinfection. The increased survival rate in Mif -/- mice was associated with less severe cachexia and anemia as a result of a mixed Th1/Th2 cytokine profile, high levels of IL-12, IL-17/IL-4, and IL-10 in serum; and high levels of IL-4 and IL-10, and low levels of IFN-γ in spleen cells compared to Py 17XL infected Wt mice. Moreover, macrophages (Mφs) from Mif -/- mice exhibited higher concentrations of IL-10 and IL-12 and reduced levels of TNF-α and nitric oxide (NO) compared to Py 17XL-infected Wt mice. These results demonstrate that MIF has an important role in regulating the immune response associated with host pathogenesis and lethality, which is relevant to consider in preventing/reducing complications in Plasmodium infections.