The role of endogenous gamma interferon (IFN-␥) in protective immunity against blood-stage Plasmodium chabaudi AS malaria was studied using IFN-␥ gene knockout (GKO) and wild-type (WT) C57BL/6 mice. Following infection with 10 6 parasitized erythrocytes, GKO mice developed significantly higher parasitemia during acute infection than WT mice and had severe mortality. In infected GKO mice, production of interleukin 12 (IL-12) p70 and tumor necrosis factor alpha in vivo and IL-12 p70 in vitro by splenic macrophages was significantly reduced compared to that in WT mice and the enhanced nitric oxide (NO) production observed in infected WT mice was completely absent. WT and GKO mice had comparable numbers of total nucleated spleen cells and B220؉ and Mac-1 ؉ spleen cells both before and after infection. Infected WT mice, however, had significantly more F4/80 ؉ , NK1.1 ؉ , and F4/80 ؉ Ia ؉ spleen cells than infected GKO mice; male WT had more CD3؉ cells than male GKO mice. In comparison with those from WT mice, splenocytes from infected GKO mice had significantly higher proliferation in vitro in response to parasite antigen or concanavalin A stimulation and produced significantly higher levels of IL-10 in response to parasite antigen. Infected WT mice produced more parasite-specific immunoglobulin M (IgM), IgG2a, and IgG3 and less IgG1 than GKO mice. Significant gender differences in both GKO and WT mice in peak parasitemia levels, mortality, phenotypes of spleen cells, and proliferation of and cytokine production by splenocytes in vitro were apparent during infection. These results thus provide unequivocal evidence for the central role of endogenous IFN-␥ in the development of protective immunity against blood-stage P. chabaudi AS.Studies of experimental murine models as well as humans suggest an important role for gamma interferon (IFN-␥) in protective immune responses to blood-stage malaria (19,22). Treatment of mice with exogenous IFN-␥ delays the onset of parasitemia and decreases the number of infected erythrocytes during Plasmodium chabaudi adami infection (4). Shear and her colleagues (31) demonstrated that daily treatment with recombinant IFN-␥ resulted in a less severe course of infection and increased survival in mice infected with the lethal strain of Plasmodium yoelii 17x. Furthermore, these investigators found a correlation between the timing and level of IFN-␥ production in vitro by spleen cells and the outcome of infection with lethal versus nonlethal strains of P. yoelii 17x. These observations were confirmed in a recent study demonstrating that endogenous levels of IFN-␥ in the spleen during blood-stage malaria infection differ between nonlethal and lethal Plasmodium species at 24 h after infection (5). Studies in our laboratory of resistant C57BL/6 and susceptible A/J mice demonstrated a correlation between the level of resistance to blood-stage P. chabaudi AS infection and IFN-␥ mRNA expression and protein production by spleen cells (15,27,34). In addition, treatment of P. chabaudi AS-infected C57BL...

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To determine whether helminth-derived products modulate dendritic cell (DC) function, we investigated the effects of excretory-secretory products (ES) and adult worm homogenate (AWH) derived from the gastrointestinal nematode Heligmosomoides polygyrus (Hp) on murine bone marrow-derived DC (BMDC). Compared to the TLR9 ligand CpG, Hp-derived products alone failed to induce DC activation. ES, but not AWH, inhibited BMDC cytokine and chemokine production and co-stimulatory molecule expression (CD40, CD86 and MHC class II) induced by TLR ligation. TLR ligand-independent, PMA-induced DC activation was unaffected by ES. Recipients of ES-treated BMDC pulsed with OVA had suppressed Ab responses in vivo, irrespective of the Th1 or Th2 isotype affiliation, compared to recipients of control OVA-pulsed BMDC. Importantly, suppression occurred even in the presence of the potent type 1 adjuvant CpG. In contrast to untreated OVA-pulsed BMDC, ES-treated BMDC pulsed with OVA had reduced co-stimulatory molecule and cytokine expression. CD4 + CD25 + Foxp3 -T cells, which secreted high IL-10 levels, were generated in co-cultures of OT-II OVAspecific TCR-transgenic CD4 + T cells and ES-treated BMDC. These IL-10-secreting T cells suppressed effector CD4 + T cell proliferation and IFN-c production, the latter effect mediated by an IL-10-dependent mechanism. Together, these results demonstrate that nematode ES impaired DC function and suppressed both Th1 and Th2 adaptive immune responses possibly by inducing regulatory T cells.

In this study, we investigated the role of endogenous IL-12 in protective immunity against blood-stage P. chabaudi AS malaria using IL-12 p40 gene knockout (KO) and wild-type (WT) C57BL/6 mice. Following infection, KO mice developed significantly higher levels of primary parasitemia than WT mice and were unable to rapidly resolve primary infection and control challenge infection. Infected KO mice had severely impaired IFN-γ production in vivo and in vitro by NK cells and splenocytes compared with WT mice. Production of TNF-α and IL-4 was not compromised in infected KO mice. KO mice produced significantly lower levels of Th1-dependent IgG2a and IgG3 but a higher level of Th2-dependent IgG1 than WT mice during primary and challenge infections. Treatment of KO mice with murine rIL-12 during the early stage of primary infection corrected the altered IgG2a, IgG3, and IgG1 responses and restored the ability to rapidly resolve primary and control challenge infections. Transfer of immune serum from WT mice to P. chabaudi AS-infected susceptible A/J mice completely protected the recipients, whereas immune serum from KO mice did not, as evidenced by high levels of parasitemia and 100% mortality in recipient mice. Furthermore, depletion of IgG2a from WT immune serum significantly reduced the protective effect of the serum while IgG1 depletion had no significant effect. Taken together, these results demonstrate the protective role of a Th1-immune response during both acute and chronic phases of blood-stage malaria and extend the immunoregulatory role of IL-12 to Ab-mediated immunity against Plasmodium parasites.