ATG Ubiquitination Is Required for Circumsporozoite Protein to Subvert Host Innate Immunity Against Rodent Malaria Liver Stage.

Although exo-erythrocytic forms (EEFs) of liver stage malaria parasite in the parasitophorous vacuole (PV) are encountered with robust host innate immunity, EEFs can still survive and successfully complete the infection of hepatocytes, and the underlying mechanism is largely unknown. Here, we showed that sporozoite circumsporozoite protein (CSP) translocated from the parasitophorous vacuole into the hepatocyte cytoplasm significantly mediated the resistance to the killing of EEFs by interferon-gamma (IFN-γ). Attenuation of IFN-γ-mediated killing of EEFs by CSP was dependent on its ability to reduce the levels of autophagy-related genes (ATGs) in hepatocytes. The ATGs downregulation occurred through its enhanced ubiquitination mediated by E3 ligase NEDD4, an enzyme that was upregulated by CSP when it translocated from the cytoplasm into the nucleus of hepatocytes via its nuclear localization signal (NLS) domain. Thus, we have revealed an unrecognized role of CSP in subverting host innate immunity and shed new light for a prophylaxis strategy against liver-stage infection.

The rodent malaria liver stage survives in the rapamycin-induced autophagosome of infected Hepa1-6 cells.

It has been reported that non-selective autophagy of infected hepatocytes could facilitate the development of malaria in the liver stage, but the fate of parasites following selective autophagy of infected hepatocytes is still not very clear. Here, we confirmed that sporozoite infection can induce a selective autophagy-like process targeting EEFs (exo-erythrocytic forms) in Hepa1-6. Rapamycin treatment greatly enhanced this process in EEFs and non-selective autophagy of infected Hepa1-6 cells and enhanced the development of the malaria liver stage in vivo. Although rapamycin promoted the fusion of autophagosomes containing the malaria parasite with lysosomes, some parasites inside the autophagosome survived and replicated normally. Further study showed that the maturation of affected autolysosomes was greatly inhibited. Therefore, in addition to the previously described positive role of rapamycin-induced nonselective autophagy of hepatocytes, we provide evidence that the survival of EEFs in the autophagosome of the infected hepatocytes also contributes to rapamycin-enhanced development of the malaria liver stage, possibly due to the suppression of autolysosome maturation by EEFs. These data suggest that the inhibition of autolysosome maturation might be a novel escape strategy used by the malaria liver stage.

Establishment of a murine model of cerebral malaria in KunMing mice infected with Plasmodium berghei ANKA.

Malaria remains one of the most devastating diseases. Cerebral malaria (CM) is a severe complication of Plasmodium falciparum infection resulting in high mortality and morbidity worldwide. Analysis of precise mechanisms of CM in humans is difficult for ethical reasons and animal models of CM have been employed to study malaria pathogenesis. Here, we describe a new experimental cerebral malaria (ECM) model with Plasmodium berghei ANKA infection in KunMing (KM) mice. KM mice developed ECM after blood-stage or sporozoites infection, and the development of ECM in KM mice has a dose-dependent relationship with sporozoites inoculums. Histopathological findings revealed important features associated with ECM, including accumulation of mononuclear cells and red blood cells in brain microvascular, and brain parenchymal haemorrhages. Blood-brain barrier (BBB) examination showed that BBB disruption was present in infected KM mice when displaying clinical signs of CM. In vivo bioluminescent imaging experiment indicated that parasitized red blood cells accumulated in most vital organs including heart, lung, spleen, kidney, liver and brain. The levels of inflammatory cytokines interferon-gamma, tumour necrosis factor-alpha, interleukin (IL)-17, IL-12, IL-6 and IL-10 were all remarkably increased in KM mice infected with P. berghei ANKA. This study indicates that P. berghei ANKA infection in KM mice can be used as ECM model to extend further research on genetic, pharmacological and vaccine studies of CM.

The TLR2 is activated by sporozoites and suppresses intrahepatic rodent malaria parasite development.

TLRs (Toll-like receptors) play an important role in the initiation of innate immune responses against invading microorganisms. Although several TLRs have been reported to be involved in the innate immune response against the blood-stage of malaria parasites, the role of TLRs in the development of the pre-erythrocytic stage is still largely unknown. Here, we found that sporozoite and its lysate could significantly activate the TLR2, and induce macrophages to release proinflammatory cytokines, including IL-6, MCP-1 and TNF-α, in a TLR2-dependent manner. Further studies showed that sporozoite and its lysate could be recognized by either TLR2 homodimers or TLR2/1 and TLR2/6 heterodimers, implicating the complexity of TLR2 agonist in sporozoite. Interestingly, the TLR2 signaling can significantly suppress the development of the pre-erythrocytic stage of Plasmodium yoelii, as both liver parasite load and subsequent parasitemia were significantly elevated in both TLR2- and MyD88-deficient mice. Additionally, the observed higher level of parasite burden in TLR2(-/-) mice was found to be closely associated with a reduction in proinflammatory cytokines in the liver. Therefore, we provide the first evidence that sporozoites can activate the TLR2 signaling, which in turn significantly inhibits the intrahepatic parasites. This may provide us with novel clues to design preventive anti-malaria therapies.

Malaria DNA vaccine gp96NTD-CSP elicits both CSP-specific antibody and CD8(+) T cell response.

It is ideal for the pre-erythrocytic stage subunit vaccine to induce both CSP-specific antibody and CD8(+) T cell response. Here, we designed a novel malaria DNA vaccine gp96NTD-CSP, which was constructed by fusing the full-length of CSP with the N-terminal domain of gp96 that deleted the endoplasmic reticulum-localized motif KDEL, and investigated its protective efficacy. We found that the fusion protein gp96NTD-CSP was mainly distributed on the surface of eukaryotic cells after transfection and could be sensed as a "danger signal" by the host immune system. Interestingly, both liver parasite burden and parasitemia in mice immunized with gp96NTD-CSP were significantly lower than those in the mice immunized either with gp96NTD, CSP, or gp96NTD-SYVPSAEQI, which was constructed by fusing the CSP-specific CD8(+) T cell epitope with the N-terminal domain of gp96 deleted with KDEL. Consistently, both the level of CSP-specific antibody and the frequency of IFN-γ secreted-CSP-specific CD8(+) T cells were much higher in mice immunized with gp96NTD-CSP than those in the mice immunized either with gp96NTD, CSP, or gp96NTD-SYVPSAEQI. Our results suggest that the malaria DNA vaccine gp96NTD-CSP could induce both humoral and cellular immune responses, which is attributed to the adjuvant effect of gp96NTD and full-length CSP.

The Plasmodium circumsporozoite protein, a novel NF-κB inhibitor, suppresses the growth of SW480.

The blocking of NF-κB activation is a promising strategy for the treatment of colorectal cancer. The circumsporozoite protein (CSP), a key component of the sporozoite stage of the malaria parasite, was recently reported to block NF-κB activation in hepatocytes. Thus, we investigated the effect of the CSP on the growth of the human colon cancer cell line, SW480. We demonstrated that transfection with a recombinant plasmid expressing CSP inhibited the proliferation of SW480 in a dose-dependent manner and induced the apoptosis of SW480. A NF-κB gene reporter assay showed that both the CSP and its nuclear localization signal (NLS) motif could equally suppress the activation of NF-κB following the stimulation with human recombinant TNF-α in the SW480. Furthermore, western blot analysis indicated that NLS did not affect the phosphorylation and degradation of IκB, but could sharply inhibit the nuclear translocation of NF-κB in TNF-α stimulated SW480. Hence, our data suggest that the CSP might be explored as a new NF-κB inhibitor for the treatment of colorectal cancer.

Plasmodium yoelii blood-stage primes macrophage-mediated innate immune response through modulation of toll-like receptor signalling.

BACKGROUND: Toll-like receptors (TLRs) signalling is reported to be primed by the infection of human malaria parasite, Plasmodium falciparum. However, little is known about the regulation of macrophages TLR signalling by the infection of lethal or non-lethal strain of rodent malaria parasites. METHODS: BALB/c mice were infected with non-lethal strain Plasmodium yoelii 17XNL or lethal strain P. yoelii 17XL. Peritoneal macrophages were isolated to study its immune response to pRBC lysate, and TLRs (TLR2, TLR4, and TLR9) agonists, and the expression of TLRs and intracellular signalling molecules were also investigated by flow cytometry and semi-quantitive RT-PCR. RESULTS: The reactivity of peritoneal macrophages from the mice infected with lethal strain P. y 17XL or non-lethal strain P. y 17XNL were enhanced to pRBC lysate, and TLR2, TLR4, and TLR9 agonists at one, three and five days post-infection. Of all the tested TLRs, only TLR2 was up-regulated on peritoneal macrophages of mice infected with either strain. However, transcription of intracellular signalling molecules MyD88, IRAK-1, and TRAF-6 was significantly up-regulated in peritoneal macrophages from mice infected either with P. yoelii 17XL or P. yoelii 17XNL at one, three and five days post-infection. However, the enhanced TLRs response of macrophage from P. yoelii 17XNL-infected mice persisted for a much longer time than that from P. yoelii 17XL-infected mice. CONCLUSION: Both P. yoelii 17XL and 17XNL strains could enhance the response of peritoneal macrophages to pRBC lysate and TLR agonists, through up-regulating the expression of TLR2 and intracellular signalling molecules MyD88, IRAK-1, and TRAF-6. In addition, prolonged high response of macrophage from P. yoelii 17XNL-infected mice might be associated with the more efficiently controlling of P. yoelii 17XNL growth in mice at early stage.

Comparative histopathology of mice infected with the 17XL and 17XNL strains of Plasmodium yoelii.

Plasmodium yoelii 17XL was used to investigate the mechanism of Plasmodium falciparum-caused cerebral malaria, although its histological effect on other mouse organs is still unclear. Here, histological examination was performed on mice infected with P. yoelii 17XL; the effect of P. yoelii 17XL infection on anemia and body weight loss, as well as its lesions in the brain, liver, kidney, lung, and spleen, also was investigated. Plasmodium yoelii 17XL-infected red blood cells were sequestered in the microcirculation of the brain and in the kidney. Compared with the nonlethal P. yoelii 17XNL strain, infection by P. yoelii 17XL caused substantial pulmonary edema, severe anemia, and significant body weight loss. Although P. yoelii 17XNL and 17XL produced a similar focal necrosis in the mouse liver, infection of P. yoelii 17XL induced coalescing of red and white pulp. Mortality caused by P. yoelii 17XL may be due to cerebral malaria, as well as respiratory distress syndrome and severe anemia. Plasmodium yoelii 17XL-infected rodent malaria seems to be a useful model for investigating severe malaria caused by P. falciparum.

Bone marrow mesenchymal stem cells can be mobilized into peripheral blood by G-CSF in vivo and integrate into traumatically injured cerebral tissue.

The efficacy of granulocyte colony-stimulating factor (G-CSF) in mobilizing mesenchymal stem cells (MSCs) into peripheral blood (PB) and the ability of PB-MSCs incorporated into injured brain were tested. Colony forming, cell phenotype and differentiation potential of mouse MSCs mobilized by G-CSF (40 µg/kg) were evaluated. Mortality and pathological changes in mice with serious craniocerebral trauma plus G-CSF treatment (40 µg/kg) were investigated. Bone marrow (BM) cells derived from GFP mice were fractionated into MSCs, hematopoietic stem cells (HSCs), and non-MSC/HSCs using magnetic beads and adherent culture. The resultant cell populations were transplanted into injured mice. The in vivo integration and differentiation of the transplanted cells were detected immunocytochemically. The expression of SDF-1 in injured area of brain was tested by Western blot. G-CSF was able to mobilize MSCs into PB (fourfold increase). PB-MSCs possessed similar characteristics as BM-MSCs in terms of colony formation, the expression pattern of CD73, 44, 90, 106, 31 and 45, and multipotential of differentiation. Accumulative total mice mortality was lower in TG group (5/14) than that in T group (7/14). It was MSCs, not HSCs or non-MSC/HSC cells integrated into the damaged cerebral tissue and differentiated into cells expressing neural markers. Increased SDF-1 expression in injured area of brain was confirmed, which could facilitate the homing of MSCs to brain. G-CSF can mobilize MSCs into PB and MSCs in PB can integrate into injured cerebral tissue and transdifferentiated into neural cells and may benefit the repair of trauma.

Involvement of prophenoloxidases in the suppression of Plasmodium yoelii development by Anopheles dirus.

Anopheles dirus is refractory to a rodent malaria parasite, Plasmodium yoelii, and melanized oocysts are manifested in infected mosquitoes. Prophenoloxidase (PPO) is a zymogen whose active form mediates melanotic encapsulation of invading pathogens in mosquitoes. In this study, we cloned cDNA fragments of four An. dirus PPOs, that are orthologs of Anopheles gambiae PPO2, PPO4, PPO5 and PPO6. AdPPO4 expression in hemocytes was induced in response to P. yoelii infection. RNA interference using double stranded RNA of AdPPO4 led to depletion of its mRNA and other PPO transcripts. This depletion increased P. yoelii infection prevalence and oocyst intensity, and abolished the melanization of oocysts as well. Therefore, An. dirus PPOs may play a role in the refractoriness to P. yoelii.

[Inhibition of CpG oligodeoxynucleotide on the development of pre-erythrocytic stage of Plasmodium].

OBJECTIVE: To study the role of cytidine-phosphate-guanosine oligodeoxynucleotide (CpG ODN) on the development of Plasmodium liver stage. METHODS: Plasmodium yoelii BY265 18S rRNA was cloned, and the TaqMan real-time PCR was established on P. yoelii BY265 18S rRNA and mouse GAPDH as quantitative analysis model. The model was tested by the level of liver Plasmodium load with the liver cDNA in BALB/c mice infected by salivary gland sporozoites for 42 hours. Twelve BALB/c mice were randomly divided into CpG group, CpG control group and PBS control group which were injected respectively by ODN1826 30 microg, ODN1826 control 30 microg and 0.01 mol/L PBS 200 microl via vena caudalis. Twenty-four hours later, each mouse was inoculated with 100 sporozoites. Mice were sacrificed in 42 hours after infection, and the liver load of Plasmodium was analyzed by TaqMan real-time PCR. RESULTS: The cloned Py BY265 18S rRNA gene showed 98% similarity to Py 17XNL. The quantitative analysis model consisted by 18S rRNA and GAPDH showed positive correlation between the level of liver Plasmodium load and the sporozoite inoculation dose to mice. The Plasmodium load in CpG ODN pre-treated mice was reduced to one fifth of the control group (0.28/1.33) (P<0.05). CONCLUSION: The quantitative analysis model of TaqMan RT-PCR can detect the liver load of Plasmodium parasites, and CpG ODN can inhibit the development of its pre-erythrocytic stage.

[Inhibition of Plasmodium yoelii circumsporozoite protein on the activation of nuclear transcription factor in hepatoma cells stimulated by TNF-alpha].

OBJECTIVE: To investigate on the effect of Plasmodium yoelii (BY265 strain) circumsporozoite protein (CSP) on the activation of nuclear transcription factor KB (NF-KB) in hepatoma cells (HepG2) stimulated by TNF-alpha. METHODS: Entire coding sequence of CSP was reverse transcribed and amplified by RT-PCR with sporozoite total RNA as template, then cloned into pFLAG-CMV8 for construction of the recombinant plasmid pFLAG-CMV8-CSP. Indirect immunofluorescence staining with rabbit anti-CSP was applied to verify the expression and distribution of FLAG-CSP fusion protein in HepG2. Three groups were established for the experiment: group A with HepG2 transfected by pFLAG-CMV8 as negative control, group B with HepG2 transfected by pFLAG-CMV8 and stimulated by 100 ng/ml TNF-alpha, and group C with HepG2 transfected by pFLAG-CMV8-CSP and stimulated by 100 ng/ml TNF-alpha. Dual-luciferase assay and EMSA were performed to detect the nuclear translocation and activation of NF-kappaB, to observe if pFLAG-CMV8-CSP suppressed the activation of NF-KB in HepG2 stimulated by TNF-alpha. RESULT: The expression of pFLAG-CMV8-CSP was localized on cytoplasm of HepG2. The activity ratio of firefly luciferase to Renilla luciferase in group C (0.228 +/- 0.029) was significantly lower than both groups A (0.438 +/- 0.085) and B (0.571 +/- 0.030) (P < 0.05). EMSA showed that the band in group C was significantly weaker than group B. CONCLUSION: Plasmodium yoelii CSP localizes in the cytoplasm of HepG2 and inhibits the activation and nuclear translocation of NF-kappaB in HepG2 stimulated by TNF-alpha.

[Recombinant Plasmodium yoelii expressing green fluorescent protein in erythrocytic and mosquito stages].

OBJECTIVE: To generate recombinant Plasmodium yoelii BY265 strain which can express green fluorescent protein (GFP) in erythrocytic and mosquito stages. METHODS: Recombinant plasmid containing P. berghei ssu-rrna and GFP genes were linearized by Sac II. The linearized plasmid was introduced into the erythrocytic stage of P. yoelii by electroporation. Kunming mice were infected with the recombinant parasites. After 24-30 hours post-infection, mice were treated with 70 microg/ml of pyrimethamine intraperitoneally for 5-6 d, and tail vein blood was then collected to make smear for parasite count. The parasites were examined by PCR. Anopheles stephensi mosquitoes were used to bite mice infected with the recombinant parasite. At the 7th and 16th day after the bite, oocyst development in mosquitoes was observed by fluorescence microscopy. RESULTS: The recombinant parasites expressed GFP in erythrocytic stage, and the GFP and ssu-rrna genes were amplified by PCR in the recombinant parasites. The mosquito infection experiment showed a normal development of the recombinant parasites. CONCLUSION: Transgenic P. yoelii BY265 strain has been established with stable expression of GFP in both erythrocytic and mosquito stages.