Anti-lymphocyte antibodies in lethal mouse malaria. II. Induction of an autoantibody specific suppressor T cell by non-lethal P. yoelii

The anti-lymphocyte autoantibody response to irradiated lethal Plasmodium berghei malaria parasites in normal mice was significantly reduced when recipients were pre-treated with splenic T cells from mice recovered from a non-lethal Plasmodium yoelii infection. Suppression was specific for the autoantibody and did not affect the antibody response to the parasite. Experiments involving sequential P. yoelii-P. berghei infections in situ revealed that recovery from P. berghei was possible when the interval between the two infections was 14 days or more. This ability to recover from P. berghei correlated with a progressive reduction of anti-lymphocyte autoantibody suggesting a useful role for the suppressor cell. The possible link between suppressor cells and anti-lymphocyte autoantibodies in malaria is discussed.     

Role of immune complexes in cerebral malaria

To investigate the involvement of immune complexes in the pathogenesis of cerebral malaria, a comparative study between Plasmodium berghei infected Swiss albino mice and BALB/c mice was conducted. Rise in parasitemia was found to be same with differences in manifestation of disease and mortality, level of immune complexes and histopathology. Increased parasitized red cells with swelling of endothelial cells in the brain capillaries along with increased levels of circulating immune complexes were observed in the BALB/c mice.     

CD4+ CD25+ regulatory T cells suppress CD4+ T-cell function and inhibit the development of Plasmodium berghei-specific TH1 responses involved in cerebral malaria pathogenesis

The infection of mice with Plasmodium berghei ANKA constitutes the best available mouse model for human Plasmodium falciparum-mediated cerebral malaria, a devastating neurological syndrome that kills nearly 2.5 million people every year. Experimental data suggest that cerebral disease results from the sequestration of parasitized erythrocytes within brain blood vessels, which is exacerbated by host proinflammatory responses mediated by cytokines and effector cells including T lymphocytes. Here, T cell responses to P. berghei ANKA were analyzed in cerebral malaria-resistant and -susceptible mouse strains. CD4+ T-cell proliferation and interleukin-2 (IL-2) production in response to parasite-specific and polyclonal stimuli were strongly inhibited in cerebral malaria-resistant mice. In vitro and in vivo depletion of CD4+ CD25+ regulatory T (T(reg)) cells significantly reversed the inhibition of CD4+ T-cell proliferation and IL-2 production, indicating that this cell population contributes to the suppression of T-cell function during malaria. Moreover, in vivo depletion of T(reg) cells prevented the development of parasite-specific TH1 cells involved in the induction of cerebral malaria during a secondary parasitic challenge, demonstrating a regulatory role for this cell population in the control of pathogenic responses leading to fatal disease.     

CD8+-T-Cell Depletion Ameliorates Circulatory Shock in Plasmodium berghei-Infected Mice

The Plasmodium berghei-infected mouse model is a well-recognized model for human cerebral malaria. Mice infected with P. berghei exhibit (i) metabolic acidosis (pH < 7.3) associated with elevated plasma lactate concentrations, (ii) significant (P < 0.05) vascular leakage in their lungs, hearts, kidneys, and brains, (ii) significantly (P < 0.05) higher cell and serum glutamate concentrations, and (iv) significantly (P < 0.05) lower mean arterial blood pressures. Because these complications are similar to those of septic shock, the simplest interpretation of these findings is that the mice develop shock brought on by the P. berghei infection. To determine whether the immune system and specifically CD8(+) T cells mediate the key features of shock during P. berghei malaria, we depleted CD8(+) T cells by monoclonal antibody (mAb) treatment and assessed the complications of malarial shock. P. berghei-infected mice depleted of CD8(+) T cells by mAb treatment had significantly reduced vascular leakage in their hearts, brains, lungs, and kidneys compared with infected controls treated with rat immunoglobulin G. CD8-depleted mice were significantly (P < 0.05) protected from lactic acidosis, glutamate buildup, and diminished HCO(3)(-) levels. Although the blood pressure decreased in anti-CD8 mAb-treated mice infected with P. berghei, the cardiac output, as assessed by echocardiography, was similar to that of uninfected control mice. Collectively, our results indicate that (i) pathogenesis similar to septic shock occurs during experimental P. berghei malaria, (ii) respiratory distress with lactic acidosis occurs during P. berghei malaria, and (iii) most components of circulatory shock are ameliorated by depletion of CD8(+) T cells.     

Phagocyte-derived reactive oxygen species do not influence the progression of murine blood-stage malaria infections

Phagocyte-derived reactive oxygen species have been implicated in the clearance of malaria infections. We investigated the progression of five different strains of murine malaria in gp91(phox-/-) mice, which lack a functional NADPH oxidase and thus the ability to produce phagocyte-derived reactive oxygen species. We found that the absence of functional NADPH oxidase in the gene knockout mice had no effect on the parasitemia or total parasite burden in mice infected with either resolving (Plasmodium yoelii and Plasmodium chabaudi K562) or fatal (Plasmodium berghei ANKA, Plasmodium berghei K173 and Plasmodium vinckei vinckei) strains of malaria. This lack of effect was apparent in both primary and secondary infections with P. yoelii and P. chabaudi. There was also no difference in the presentation of clinical or pathological signs between the gp91(phox-/-) or wild-type strains of mice infected with malaria. Progression of P. berghei ANKA and P. berghei K173 infections was unchanged in glutathione peroxidase-1 gene knockout mice compared to their wild-type counterparts. The rates of parasitemia progression in gp91(phox-/-) mice and wild-type mice were not significantly different when they were treated with l-N(G)-methylarginine, an inhibitor of nitric oxide synthase. These results suggest that phagocyte-derived reactive oxygen species are not crucial for the clearance of malaria parasites, at least in murine models.     

Simultaneous increases in immune-competent cells and nitric oxide in the spleen during Plasmodium berghei infection in mice.

BACKGROUND AND PURPOSE: Nitric oxide and other reactive nitrogen intermediates (RNI) are thought to be important mediators of both immunological and pathological responses of the vertebrate host to malaria infection. The role of RNI has been studied most often by assay of stable RNI metabolites (nitrites, nitrates) in blood. This study evaluated the nature of the RNI response of mice to malaria by analyzing the subsets of immune-competent cells within the organ displaying increased RNI in vivo. METHODS: We measured RNI production indirectly, as stable metabolites of nitric oxide activity in tissue homogenates (brain, liver, spleen) from mice infected with Plasmodium berghei. Only spleen exhibited an RNI concentration response during rising parasitemia. Subsets of immune-competent cells (B cells, CD19+), macrophages/monocytes (MOMA2+) and T cells (CD4+, CD8+) in the spleen were assayed by fluorescence activated cell scan flow cytometry. RESULTS: The spleen was confirmed as a major source of RNI during mid-phase P. berghei infection. Significant increases in CD19+ and MOMA2+ spleen cells were evident during the mid-phase of P. berghei infection in MF1 mice when RNI are maximally elevated. CONCLUSIONS: The time courses of the cellular and RNI responses indicate that CD19+ and MOMA2+ cells may be responsible for the increase in RNI in the spleen. However, experiments in vitro are needed to make a definitive identification of the cell type(s) responsible for the increase in RNI in the mouse spleen during P. berghei infection.     

伯氏疟原虫感染早期的根治性治疗对再感染细胞免疫应答的影响

目的探讨疟疾感染早期根治性治疗对再感染细胞免疫应答的影响。方法用伯氏疟原虫感染DBA/2小鼠,感染后3d进行根治性治疗,并于初次感染后90d进行再感染。通过吉姆萨薄血膜染色法计数红细胞感染率,流式细胞术检测再感染前（0d）和再感染后（1、3、5d）不同时间点脾T细胞中活化性T细胞百分含量,ELISA检测脾细胞培养上清中IFN-γ、TNF-α、IL-4和IL-10水平。结果同源疟原虫再感染后,根治性治疗小鼠仅出现短暂的低水平虫体血症;再感染后第1～5天活化性T细胞百分率持续升高。IFN-γ于再感染后第1天即出现有意义的升高,第3天达到峰值水平,与此同时,TNF-α和IL-10水平也开始出现有意义的升高,但IL-4的升高出现在再感染后的第5天。结论疟疾感染早期的根治性治疗并不影响宿主在再感染时产生有效的细胞免疫应答,CD4＋Th1应答反应也是抵御疟疾再感染的关键因素之一。     

Splenic gammadelta T cells regulated by CD4+ T cells are required to control chronic Plasmodium chabaudi malaria in the B-cell-deficient mouse

Little is known about the function and regulation of splenic gammadelta T cells during chronic Plasmodium chabaudi malaria. The splenic gammadelta T-cell population continues to expand, reaching levels equal to 4 times the number of splenocytes in an uninfected mouse. Splenic gammadelta T cells from J(H)-/- mice with chronic malaria expressed Vgamma1+ or Vdelta4+ in the same ratio as uninfected controls with Vgamma1 cells dominating, but the Vgamma2 ratio declined about twofold. Gammadelta T cells from G8 mice specific for the TL antigen increased only 2-fold in number, compared with 10-fold in BALB/c controls, but G8 gammadelta T cells failed to express the B220 activation marker. Elimination of the parasite by drug treatment caused a slow depletion in the number of splenic gammadelta, CD4+, and CD8+ T cells. Following challenge, drug-cured J(H)-/- mice exhibited nearly identical parasitemia time courses as na?ve controls. Depletion of either CD4+ T cells or gammadelta T cells from chronically infected J(H)-/- mice by monoclonal antibody treatment resulted in an immediate and significant (P < 0.05) exacerbation of parasitemia coupled with a marked decrease in splenic gammadelta T-cell numbers. The number of CD4+ T cells, in contrast, did not decrease in mice after anti-T-cell receptor gammadelta treatment. The results indicate that cell-mediated immunity against blood-stage malarial parasites during chronic malaria (i) requires the continued presence of blood-stage parasites to remain functional, (ii) is dependent upon both gammadelta T cells and CD4+ T cells, and (iii) lacks immunological memory.     

调节性T细胞修饰前炎症应答对小鼠脑型疟疾发生的影响

为探讨调节性T细胞（Tregs）对伯氏疟原虫感染所致鼠脑型疟发生和感染结局的影响机制,用伯氏疟原虫ANKA株分别感染对照组和抗CD25单克隆抗体注射组C57BL／6小鼠,计数红细胞感染率;感染前和感染后3、5、8天制备脾细胞悬液,流式细胞术检测脾Tregs百分含量;ELISA和Griess方法检测脾细胞培养上清IFN-γ、IL-10和NO水平。结果表明大多数C57BL／6鼠于感染后8—11天死于脑疟,抗CD25单克隆抗体注射组小鼠感染后3～4周死于贫血和过度原虫血症。对照组小鼠脾细胞培养上清IFN-γ、NO、IL—10水平于感染后开始升高,感染后5天达到峰值,感染后8天与感染后5天相比,IFN-γ、NO轻微下降,IL-10显著下降。感染后3、5天,实验组IFN-γ、NO水平显著高于对照组,IL—10水平显著低于对照组。感染后8天,实验组和对照组IFN-γ、NO、IL-10水平得到逆转。这表明Tregs通过修饰前炎症应答影响伯氏疟原虫感染鼠脑型疟发生和感染结局。     

B cells are required for the switch from Th1- to Th2-regulated immune responses to Plasmodium chabaudi chabaudi infection.

The induction of T-helper cell subsets during the course of blood stage Plasmodium chabaudi chabaudi infection was compared in immunologically intact NIH mice and mice that were depleted of B cells from birth by treatment with anti-mu antibodies. For intact mice, in which the acute primary parasitemia peaked 10 days following infection, purified splenic CD4+ T cells recovered during the ascending parasitemia produced high levels in vitro of interleukin 2 (IL-2) (peak levels on day 10) and gamma interferon (IFN-gamma) (peak levels on day 7). Sera collected from these mice at around this time contained relatively high levels of P. c. chabaudi-specific immunoglobulin 2a (peak levels on day 12), and serum nitric oxide activity was significantly elevated at peak parasitemia. During the descending primary parasitemia, production of IFN-gamma and IL-2 decreased, while levels of IL-4 and IL-10 produced by splenic CD4+ T cells were significantly raised from the time at which subpatency was recorded (day 17) and persisted for at least 50 days. This was concomitant with a significant increase in levels of parasite-specific immunoglobulin G1, which peaked at around the time of recrudescence. Thus, in normal mice, sequential appearance of Th1 and Th2 responses was observed. In contrast, in B-cell-depleted mice, recovery from acute primary parasitemia was followed by a persistent patent infection which did not drop below 0.1% for at least 75 days after initiation of infection. These mice were unable to mount a significant Th2 response, manifest as an enduring inability of splenic CD4+ T cells to produce significant levels of IL-4 and IL-10. IL-2 and IFN-gamma levels remained significantly elevated throughout the 50-day observation period, and there was sustained production of nitric oxide. These data show that immune responses mediated by CD4+ T cells of the Th1 subset are capable of limiting infection beyond the initial acute phase, but that they do not eliminate parasitemia. Furthermore, as the progression from a Th1-regulated to a Th2-regulated immune response fails to occur in B-cell-depleted mice, the data suggest that B cells are required for the downregulation of Th1-mediated and/or the generation of Th2-mediated protective immunity to P. c. chabaudi.     

Production of IFN-γ by CD4(+) T cells in response to malaria antigens is IL-2 dependent

T-cell immune responses are critical for protection of the host and for disease pathogenesis during infection with Plasmodium species. We examined the regulation of CD4(+) T-cell cytokine responses during infection with Plasmodium berghei ANKA (PbA). CD4(+) T cells from PbA-infected mice produced IFN-γ, IL-4 and IL-10 in response to TCR stimulation at levels higher than those from uninfected mice. This altered cytokine response was dependent on parasitemia. To examine the specificity of the response, mice were adoptively transferred with CD4(+) T cells from OT-II TCR transgenic mice and were infected with PbA expressing OVA. Unexpectedly, CD4(+) T cells from the OT-II-transferred wild-type PbA-infected mice showed high levels of IFN-γ production after stimulation with OVA and the cells producing IFN-γ were not OT-II but were host CD4(+) T cells. Further investigation revealed that host CD4(+) T cells produced IFN-γ in response to IL-2 produced by activated OT-II cells. This IFN-γ response was completely inhibited by anti-CD25 mAbs, and this effect was not due to the block of the survival signals provided by IL-2. Furthermore, IFN-γ production by CD4(+) T cells in response to PbA antigens was dependent on IL-2. These findings suggest the importance of IL-2 levels during infection with malaria parasites and indicate that CD4(+) T cells can produce IFN-γ without TCR engagement via a bystander mechanism in response to IL-2 produced by other activated CD4(+) T cells.     

Cell-mediated immunity to the asexual blood stages of malarial parasites: animal models

Studies using experimental models of malaria in immunodeficient mice and chickens have shown that resistance to blood-stage infection is mediated by protective antibodies and T cell-dependent cell-mediated mechanisms of immunity. Depending on the infecting species of Plasmodium and prior experience of the host, either humoral or cell-mediated immune mechanisms predominate. Cell-mediated immunity has been adoptively transferred with CD4+ splenic T cells, and with antigen-specific T cell lines and clones. Since ascending parasitemia occurs in all instances, the transferred cells do not kill plasmodia directly but appear to activate effector mechanisms capable of destroying the invading parasites. Both CD4+ and CD8+ T cells were found to increase in the spleens of malarious mice. Depletion of CD4+ T cells prevented nude mice adoptively transferred with immune splenic T cells from clearing parasitemia. In contrast, late treatment with anti-CD4 antibody had little if any effect. The converse was true when anti-CD8 antibody was utilized, i.e., a significant number of mice treated with anti-CD8 antibody after parasitemia became patent and had difficulty clearing blood parasites. These data suggest that during infection CD8+ T cells may become activated by CD4+ T cells responding to malarial antigens. These CD8+ T cells may be directly cytotoxic or secrete additional cytokines thereby amplifying the role of CD4+ T cells in the activation of anti-parasite effector mechanisms. Finally, a hypothesis is presented to explain how the parasite in natural infections may activate T cell-dependent effector mechanisms in order to control its numbers in host tissues thereby ensuring the survival of both parasite and host.     

Prevention of experimental cerebral malaria by Flt3 ligand during infection with Plasmodium berghei ANKA

Dendritic cells are the most potent antigen-presenting cells, but their roles in blood-stage malaria infection are not fully understood. We examined the effects of Flt3 ligand, a cytokine that induces dendritic cell production, in vivo on the course of infection with Plasmodium berghei ANKA. Mice treated with Flt3 ligand showed preferential expansion of CD8(+) dendritic cells and granulocytes, as well as lower levels of parasitemia, and were protected from the development of lethal experimental cerebral malaria (ECM). Rag2 knockout mice treated with Flt3 ligand also showed inhibition of parasitemia, suggesting that this protection was due, at least in part, to the stimulation of innate immunity. However, it was unlikely that the inhibition of ECM was due simply to the reduction in the level of parasitemia. In the peripheral T cell compartment, CD8(+) T cell levels were markedly increased in Flt3 ligand-treated mice after infection. These CD8(+) T cells expressed CD11c and upregulated CXCR3, while the expression of CD137, CD25, and granzyme B was reduced. In the brain, the number of sequestered CD8(+) T cells was not significantly different for treated versus untreated mice, while the proportion of CD8(+) T cells that produce gamma interferon (IFN-γ) and granzyme B was significantly reduced in treated mice. In addition, sequestration of parasitized red blood cells (RBCs) in the brain was reduced, suggesting that altered CD8(+) T cell activation and reduced sequestration of parasitized RBCs culminated in inhibition of ECM development. These results suggest that the quantitative and qualitative changes in the dendritic cell compartment are important for the pathogenesis of ECM.     

Differential sensitivity in vivo of lethal and nonlethal malarial parasites to endotoxin-induced serum factor.

Sera from mice infected with Plasmodium yoelii or Plasmodium berghei and given endotoxin contained nonspecific mediators which killed both species of parasite and tumor cells in vitro. The sera resembled tumor necrosis sera obtained from mice given macrophage-activating agents such as Propionibacterium acnes (formerly designated Corynebacterium acnes) or Mycobacterium bovis BCG and then endotoxin. Cytotoxicity developed parallel to parasite killing activity and indicated that macrophages were activated. Activation occurred sooner with P. berghei, which is lethal, and serum activity remained on a plateau until the mice died. In nonlethal P. yoelii infections, activation was related to the course of parasitemia. Endotoxin given to mice infected with P. yoelii caused an immediate decrease in parasitemia, presumably through the release of parasite killing factors. The extent of the decrease depended upon the time of administration. No immediate drop in the parasitemia caused by P. berghei was observed at any time. Early administration of endotoxin prolonged survival; late administration accelerated death. Passive transfer of rabbit tumor necrosis serum to infected mice decreased the parasitemia caused by P. yoelii but not that caused by P. berghei. Other components of the immune response appeared to act together with these soluble mediators to eliminate P. yoelii; they may be absent or suppressed in infections with P. berghei.     

Gamma interferon production is critical for protective immunity to infection with blood-stage Plasmodium berghei XAT but neither NO production nor NK cell activation is critical

We have examined the roles of gamma interferon (IFN-gamma), nitric oxide (NO), and natural killer (NK) cells in the host resistance to infection with the blood-stage malarial parasite Plasmodium berghei XAT, an irradiation-induced attenuated variant of the lethal strain P. berghei NK65. Although the infection with P. berghei XAT enhanced NK cell lytic activity of splenocytes, depletion of NK1.1(+) cells caused by the treatment of mice with anti-NK1.1 antibody affected neither parasitemia nor IFN-gamma production by their splenocytes. The P. berghei XAT infection induced a large amount of NO production by splenocytes during the first peak of parasitemia, while P. berghei NK65 infection induced a small amount. Unexpectedly, however, mice deficient in inducible nitric oxide synthase (iNOS-/-) cleared P. berghei XAT after two peaks of parasitemia were observed, as occurred for wild-type control mice. Although the infected iNOS-/- mouse splenocytes did not produce a detectable level of NO, they produced an amount of IFN-gamma comparable to that produced by wild-type control mouse splenocytes, and treatment of these mice with neutralizing anti-IFN-gamma antibody led to the progression of parasitemia and fatal outcome. CD4(-/-) mice infected with P. berghei XAT could not clear the parasite, and all these mice died with apparently reduced IFN-gamma production. Furthermore, treatment with carrageenan increased the susceptibility of mice to P. berghei XAT infection. These results suggest that neither NO production nor NK cell activation is critical for the resistance to P. berghei XAT infection and that IFN-gamma plays an important role in the elimination of malarial parasites, possibly by the enhancement of phagocytic activity of macrophages.     

P-selectin contributes to severe experimental malaria but is not required for leukocyte adhesion to brain microvasculature

Plasmodium berghei-infected mice, a well-recognized model of experimental cerebral malaria (ECM), exhibit many of the hallmarks of a systemic inflammatory response, with organ damage in brain, lung, and kidneys. Identification of the molecules mediating pathogenesis of the inflammatory response, such as leukocyte adhesion, may lead to new therapies. Indeed, mice lacking the cell adhesion molecule P-selectin were significantly (P = 0.005) protected from death due to P. berghei malaria compared with C57BL/6 controls despite similar parasitemia (P = 0.6) being found in both groups of mice. P-selectin levels assessed by the quantitative dual radiolabeled monoclonal antibody technique increased significantly (P < 0.05) in several organs in C57BL/6 mice infected with P. berghei, supporting the concept of a systemic inflammatory response mediating malarial pathogenesis. Intravital microscopic analysis of the brain microvasculature demonstrated significant (P < 0.001) leukocyte rolling and adhesion in brain venules of P. berghei-infected mice compared with those found in uninfected controls. The maximum leukocyte adhesion occurred on day 6 of P. berghei infection, when the mice become moribund and exhibit marked vascular leakage into the brain, lung, and heart. However, P-selectin levels were significantly (P < 0.005) increased in brain, lung, and kidneys during P. berghei malaria in ECM-resistant BALB/c mice compared with those found in uninfected BALB/c controls, indicating that increased P-selectin alone is not sufficient to mediate malarial pathogenesis. Leukocyte adhesion to brain microvessels of P-selectin-deficient mice with P. berghei malaria was similar to that observed in control mice. Collectively, these results indicate that P-selectin is important for the development of malarial pathogenesis but is not required for leukocyte adhesion in brain.     

Spleen cell changes during fatal and self-limiting malarial infections of mice.

Changes in the proportions and total numbers of splenic Thy-1.2+ cells, Ig+ cells and normoblasts were analysed during fatal Plasmodium berghei and non-fatal P. yoelii infections in mice. Thy-1.2+ and Ig+ cells were identified by rosetting techniques, and normoblasts by morphological criteria. The splenomegaly observed during these infections was found to be caused mainly by proliferation of normoblasts. An early increase in the numbers of Thy-1.2+ and Ig+ cells was detected in both infections, but in P. berghei infections these responses were subsequently suppressed. In P. yoelii infections Thy-1.2+ and Ig+ cell numbers were maintained at four to five-fold above normal levels until the mice had completely recovered. During the acute phase of P. yoelii infection it appeared that most splenic T-cells expressed surface immunoglobulin.     

Class II-restricted protective immunity induced by malaria sporozoites

The irradiated-sporozoite vaccine elicits sterile immunity against Plasmodium parasites in experimental rodent hosts and human volunteers. Based on rodent malaria models, it has been proposed that CD8+ T cells are the key protective effector mechanism required in sporozoite-induced immunity. To investigate the role of class II-restricted immunity in protective immunity, we immunized beta2-microglobulin knockout (beta2M-/-) mice with irradiated Plasmodium yoelii or P. berghei sporozoites. Sterile immunity was obtained in the CD8+-T-cell-deficient mice immunized with either P. berghei or P. yoelii sporozoites. beta2M-/- mice with the BALB/c (H-2d) genetic background as well as those with the C57BL (H-2b) genetic background were protected. Effector mechanisms included CD4+ T cells, mediated in part through the production of gamma interferon, and neutralizing antibodies that targeted the extracellular sporozoites. We conclude that in the absence of class I-restricted CD8+ T cells, sporozoite-induced protective immunity can be effectively mediated by class II-restricted immune effector mechanisms. These results support efforts to develop subunit vaccines that effectively elicit high levels of antibody and CD4+ T cells to target Plasmodium pre-erythrocytic stages.     

Stromal cell-derived factor-1 production by spleen cells is affected by nitric oxide in protective immunity against blood-stage Plasmodium chabaudi CR in C57BL/6j mice

Malaria, a major endemic tropical disease, is caused by the infection of blood cells by Plasmodium protozoa. Most patients control their parasitemia by a not fully understood spleen-dependent mechanism. SDF-1alpha is a chemokine produced by stromal cells such as reticular spleen cells. Nitric oxide (NO) has several immune functions, including killing of intracellular pathogens and its function in malaria is debated. We have previously shown that SDF-1alpha production peaks during the ascending parasitemia in Plasmodium chabaudi infection and its supplementation in lethal models could reduce the parasitemia. In the present study, we analyzed SDF-1 production by spleen cells as related to NO metabolism in the P. chabaudi rodent malaria model using IFN-gamma; TNFR and iNOS-knockout mice or iNOS-blocked, L-NAME- or aminoguanidine-treated mice. Parasitemia and production of SDF-1alpha and SDF-1beta were determined by RT-PCR. In vitro NO production by spleen adherent cells was also tested. The data showed that parasitemia was less intense in both iNOS(-/-) or NO-inhibited mice than in controls, with increased and long-lasting production of SDF-1alpha mRNA. In the absence of cytokines involved in the final regulation of NO production by effector cells, as is the case for TNFR(-/-) and GKO mice, the infection progressed in an uncontrolled manner regardless of SDF-1alpha production, suggesting that these cytokines must be involved in the control of parasitemia after the SDF-1alpha dependent process. The SDF-1beta isoform was constitutive in all experiments, with elevated levels only clearly seen in TNFR(-/-) mice. We conclude that SDF-1 is involved in the promotion of parasitemia control in malaria, and excessive NO could affect its production.