Activation of Tregs during infection with PyL requires TLR9 signaling in DCs 10. It is quite possible that Tregs are not activated in IDA mice due to insufficient TLR9 signaling because IDA erythrocytes contain much less hemoglobin/heme (data not shown), the source of a known malaria-derived TLR9 ligand, hemozoin 11. Thus, we analyzed the immune responses in IDA mice. First, we assessed the number of cells

find more involved in protection against malaria in the spleen 6 days after infection with PyL (Fig. 3A). Infection with PyL clearly increased the population of spleen cells. Unexpectedly, the number of whole splenocytes and splenic CD4+CD25– T cells in IDA mice was less than that in control mice. There was no increase in the number of macrophages. IFN-γ production by whole spleen cells in response to ConA

was evaluated using ELISA. Infection of control mice with PyL markedly reduced the production of IFN-γ; however, infection Crizotinib of IDA mice reduced it to an even greater degree (Fig. 3B). The production of IgG antibodies specific for the malaria parasite was also assessed. Humoral immunity to the malaria parasite was induced after infection with PyL in iron-sufficient mice. However, IDA mice had much lower total IgG levels (Fig. 3C). Thus, neither humoral nor cellular responses were enhanced in IDA mice. We further evaluated the functional properties of splenic Tregs by investigating the suppression of TCR-driven T-cell proliferation. CD4+CD25+ T cells isolated from IDA mice were Pregnenolone cultured with CD4+CD25− T cells from uninfected mice in the presence of ConA. Tregs from uninfected mice suppressed proliferation in a dose-dependent manner. Infection of iron-sufficient mice with PyL markedly enhanced the suppressive function of Tregs, reflecting Treg activation

(Fig. 3D). Tregs in IDA mice had much stronger suppressive abilities (Fig. 3D), presumably resulting in reduced immune responses in these mice. Again, we saw no evidence for the enhancement of acquired immunity in IDA mice. Finally, to analyze whether acquired immunity is involved in the resistance of IDA mice to malaria, we infected T-cell and iron-deficient athymic nude mice with PyL. As shown previously, IDA euthymic mice showed lower levels of parasitemia and prolonged survival compared with euthymic mice fed with an iron-sufficient diet (Fig. 3E). IDA athymic mice clearly showed lower levels of parasitemia than mice fed with an iron-sufficient diet although they still succumbed to infection with PyL. These results suggest that acquired immunity, in which T cells play a central role, is required to survive infection by PyL, but it is not involved in IDA-associated resistance to malaria during the early phase of infection.