Rapid detection and quantification of Ebola Zaire virus by one-step real-time quantitative reverse transcription-polymerase chain reaction.

Given that Ebola virus causes severe hemorrhagic fever in humans with mortality rates as high as 90%, rapid and accurate detection of this virus is essential both for controlling infection and preventing further transmission. Here, a one-step qRT-PCR assay for rapid and quantitative detection of an Ebola Zaire strain using GP, VP24 or VP40 genes as a target is introduced. Routine assay conditions for hydrolysis probe detection were established from the manufacturer's protocol used in the assays. The analytical specificity and sensitivity of each assay was evaluated using in vitro synthesized viral RNA transcripts. The assays were highly specific for the RNA transcripts, no cross-reactivity being observed among them. The limits of detection of the assays ranged from 102 to 103 copies per reaction. The assays were also evaluated using viral RNAs extracted from cell culture-propagated viruses (Ebola Zaire, Sudan and Reston strains), confirming that they are gene- and strain-specific. The RT-PCR assays detected viral RNAs in blood samples from virus-infected animal, suggesting that they can be also a useful method for identifying Ebola virus in clinical samples.

Identification of novel therapeutic target genes in acquired lapatinib-resistant breast cancer by integrative meta-analysis.

Acquired resistance to lapatinib is a highly problematic clinical barrier that has to be overcome for a successful cancer treatment. Despite efforts to determine the mechanisms underlying acquired lapatinib resistance (ALR), no definitive genetic factors have been reported to be solely responsible for the acquired resistance in breast cancer. Therefore, we performed a cross-platform meta-analysis of three publically available microarray datasets related to breast cancer with ALR, using the R-based RankProd package. From the meta-analysis, we were able to identify a total of 990 differentially expressed genes (DEGs, 406 upregulated, 584 downregulated) that are potentially associated with ALR. Gene ontology (GO) function and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis of the DEGs showed that "response to organic substance" and "p53 signaling pathway" may be largely involved in ALR process. Of these, many of the top 50 upregulated and downregulated DEGs were found in oncogenesis of various tumors and cancers. For the top 50 DEGs, we constructed the gene coexpression and protein-protein interaction networks from a huge database of well-known molecular interactions. By integrative analysis of two systemic networks, we condensed the total number of DEGs to six common genes (LGALS1, PRSS23, PTRF, FHL2, TOB1, and SOCS2). Furthermore, these genes were confirmed in functional module eigens obtained from the weighted gene correlation network analysis of total DEGs in the microarray datasets ("GSE16179" and "GSE52707"). Our integrative meta-analysis could provide a comprehensive perspective into complex mechanisms underlying ALR in breast cancer and a theoretical support for further chemotherapeutic studies.

Characterization of pncA mutations in pyrazinamide-resistant Mycobacterium tuberculosis isolates from Korea and analysis of the correlation between the mutations and pyrazinamidase activity.

To investigate the effect of natural pyrazinamidase (PncA) mutations on protein function, we analyzed expression and PncA activity of eight pncA point mutants identified in nineteen pyrazinamide-resistant Mycobacterium tuberculosis clinical isolates. Among them, two mutants (Y99D and T135P) showed high expression level and solubility comparable to those of the wild-type PncA protein, two (K48E and G97D) displayed low expression level and solubility, and four (C14R, H51P, W68S, and A146V) were insoluble. Interestingly, when possible structural effects of these mutations were predicted by the CUPSAT program based on the proposed three-dimensional structure of M. tuberculosis PncA, only two highly soluble mutant proteins (Y99D and T135P) were predicted to be stabilizing and have favorable torsion angles. However, the others exhibiting either low solubility or precipitation were foreseen to be destabilizing and/or have unfavorable torsion angles, suggesting that the alterations could interfere with proper protein folding, thereby decreasing or depleting protein solubility. A PncA activity assay demonstrated that two mutants (G97D and T135P) showed virtually no activity, but two other mutants (K48E and Y99D) exhibited wild-type activity, indicating that the PncA residues (Cys14, His51, Trp68, Gly97, Thr135, and Ala146) may be important for PncA activity and/or proper protein folding.

Transcriptional induction of TGF-ß1 and endothelial-to-mesenchymal transition cell markers in human umbilical vein endothelial cells by Ebola virus infection.

BACKGROUND: Ebola virus (EBOV) causes a serious hemorrhagic disease in humans, with a mortality rate of up to 80%. Despite significant achievements in the past decades elucidating the pathogenesis of EBOV, there is still much to be elucidated about the cell type-specific host response and their functional roles during infection. OBJECTIVE: This study aimed to gain insight into cell type-specific host responses to EBOV infection. METHODS: Real-time RT-qPCR analysis was used to identify host transcriptional changes in epithelial Caco-2 cells and endothelial HUVECs by EBOV infection. RESULTS: EBOV efficiently infected to both Caco-2 cells and HUVECs, depending on the time of infection. However, changes in the transcriptional levels of several host cellular genes following viral infection showed significant differences between Caco-2 cells and HUVECs. EBOV infection increases the transcription of TGF-ß1, a key factor in epithelium-to-mesenchyme transition (EMT), only in HUVECs, but not in Caco-2 cells. This upregulation in turn induces the transcription of other EMT signaling molecules such as snail, slug and MMP9, ultimately leading to endothelial-to-mesenchymal transition (EndMT). Furthermore, this EndMT process appears to be associated with increased transcription of stem-cell markers such as Klf4, Sox2 and Oct4. However, most of these transcriptional changes due to EBOV infection did not occur in Caco-2 cells, suggesting that EMT or EndMT by EBOV infection is cell type-specific. CONCLUSION: We propose that EBOV infection induces the expression of TGF-ß1-mediated signals in endothelial HUVECs, resulting in EndMT. This could provide broader information to elucidate the pathogenesis of Ebola virus disease.

Akt regulates the expression of MafK, synaptotagmin I, and syntenin-1, which play roles in neuronal function.

BACKGROUND: Akt regulates various cellular processes, including cell growth, survival, and metabolism. Recently, Akt's role in neurite outgrowth has also emerged. We thus aimed to identify neuronal function-related genes that are regulated by Akt. METHODS: We performed suppression subtractive hybridization on two previously established PC12 sublines, one of which overexpresses the wild-type (WT) form and the other, the dominant-negative (DN) form of Akt. These sublines respond differently to NGF's neuronal differentiation effect. RESULTS: A variety of genes was identified and could be classified into several functional groups, one of which was developmental processes. Two genes involved in neuronal differentiation and function were found in this group. v-Maf musculoaponeurotic fibrosarcoma oncogene homolog K (MafK) induces the neuronal differentiation of PC12 cells and immature telencephalon neurons, and synaptotagmin I (SytI) is essential for neurotransmitter release. Another gene, syntenin-1 (Syn-1) was also recognized in the same functional group into which MafK and SytI were classified. Syn-1 has been reported to promote the formation of membrane varicosities in neurons. Quantitative reverse transcription polymerase chain reaction analyses show that the transcript levels of these three genes were lower in PC12 (WT-Akt) cells than in parental PC12 and PC12 (DN-Akt) cells. Furthermore, treatment of PC12 (WT-Akt) cells with an Akt inhibitor resulted in the increase of the expression of these genes and the improvement of neurite outgrowth. These results indicate that dominant-negative or pharmacological inhibition of Akt increases the expression of MafK, SytI, and Syn-1 genes. Using lentiviral shRNA to knock down endogenous Syn-1 expression, we demonstrated that Syn-1 promotes an increase in the numbers of neurites and branches. CONCLUSIONS: Taken together, these results indicate that Akt negatively regulates the expression of MafK, SytI, and Syn-1 genes that all participate in regulating neuronal integrity in some way or another.

Heterogeneity in liver histopathology is associated with GSK-3ß activity and mitochondrial dysfunction in end-stage diabetic rats on differential diets.

While liver histopathology is heterogeneous in diabetes, the underlying mechanisms remain unclear. We investigated whether glycemic variation resulting from differential diets can induce heterogeneity in diabetic liver and the underlying molecular mechanisms. We generated end-stage non-obese diabetic model rats by subtotal-pancreatectomy in male Sprague- Dawley rats and ad libitum diet for 7 weeks (n = 33). The rats were then divided into three groups, and fed a standard- or a low-protein diet (18 or 6 kcal%, respectively), for another 7 weeks: to maintain hyperglycemia, 11 rats were fed ad libitum (18AL group); to achieve euglycemia, 11 were calorierestricted (18R group), and 11 were both calorie- and proteinrestricted with the low-protein diet (6R group). Overnightfasted liver samples were collected after the differential diets together with sham-control (18S group), and histology and molecular changes were compared. Hyperglycemic-18AL showed glycogenic hepatopathy (GH) without steatosis, with the highest GSK-3ß inactivation because of Akt activation during hyperglycemia; mitochondrial function was not impaired, compared to the 18S group. Euglycemic-18R showed neither GH nor steatosis, with intermediate GSK-3ß activation and mitochondrial dysfunction. However, euglycemic-6R showed both GH and steatosis despite the highest GSK-3ß activity and no molecular evidence of increased lipogenesis or decreased ApoB expression, where mitochondrial dysfunction was highest among the groups. In conclusion, heterogeneous liver histopathology developed in end-stage non-obese diabetic rats as the glycemic levels varied with differential diets, in which protein content in the diets as well as glycemic levels differentially influenced GSK-3ß activity and mitochondrial function in insulin-deficient state. [BMB Reports 2020; 53(2): 100-105].

Purification and characterization of a copper-containing amine oxidase from Mycobacterium sp. strain JC1 DSM 3803 grown on benzylamine.

A bacterial semicarbazide-sensitive amine oxidase (SSAO) was purified and characterized from Mycobacterium sp. strain JC1 DSM 3803 grown on benzylamine. During the purification procedures, the enzyme was tending to aggregate and exhibited heterogeneity in native PAGE. The heterogeneous forms having amine oxidase (AO) activity could be separated by their native molecular weights using gel-filtration chromatography. Most of the AOs behaved as dimers (M(r) 150,000) composed of a 75-kDa subunit, but some aggregated to form tetramers (M(r) 300,000). Besides their native molecular weight, subunit composition and V(max) value, both forms (dimer and tetramer) have almost identical biochemical properties (e.g. subunit size, optimum pH and temperature, activation energy, K(m) value on benzylamine, substrate and inhibitor specificities). When AO activity was observed by activity staining, the best-oxidized substrate was benzylamine, although the AO also oxidized tyramine and histamine. The AO was strongly inhibited by semicarbazide and isoniazid, but KCN did not affect its activity. The purified enzyme was shown to contain 2.39 mol of copper per mole of subunit, but there were no evidences of topaquinone co-factor involvement, when tested by absorption spectrum analysis and redox-cycling staining for quinoprotein detection.

Salmonella­induced miR­155 enhances necroptotic death in macrophage cells via targeting RIP1/3.

Salmonella enterica serovar Typhimurium (hereafter referred to as Salmonella), a virulent pathogen, is known to induce host­cell death. Using reverse transcription­quantitative polymerase chain reaction, a 28­fold increase of microRNA (miR)­155 expression in RAW 264.7 macrophages was observed following infection with Salmonella for 24 h. This miR­155 upregulation increased macrophage cell death by up to 40% in 48 h following infection. Western blot analysis revealed that receptor interacting protein 1 (RIP1) and 3 (RIP3) were increased at 18 h following miR­155 transfection to macrophages, similar to Salmonella infection. In addition, inhibition of RIP1 by pre­incubating macrophages with necrostatin­1, a RIP1 specific inhibitor, increased the viability of Salmonella­infected cells and miR­155­transfected cells by up to 20%. The cleavage of poly (adenosine diphosphate­ribose) polymerase­1 (PARP­1) was also enhanced by miR­155 induction upon Salmonella infection. Therefore, it was suggested that RIP1/3­induced necroptosis and PARP­1­mediated necrosis caused by miR­155 induction may represent distinct routes of programmed necrotic cell death of Salmonella­infected macrophages.

Presence of an inducible semicarbazide-sensitive amine oxidase in Mycobacterium sp. Strain JC1 DSM 3803 grown on benzylamine.

Mycobacterium sp. strain JC1 was capable of growth on benzylamine as a sole source of carbon and energy. The primary deamination of benzylamine was mediated by an inducible amine oxidase, which can also oxidize tyramine, histamine, and dopamine. Inhibitor study identified this enzyme as a copper-containing amine oxidase sensitive to semicarbazide.

Cloning and molecular characterization of GroESL heat-shock operon in methylotrophic bacterium Methylovorus Sp. strain SS1 DSM 11726.

The groESL bicistronic operon of a restricted facultative methylotrophic bacterium Methylovorus sp. strain SS1 DSM 11726 was cloned and characterized. It was found to consist of two ORFs encoding proteins with molecular masses of 11,395 and 57,396 daltons, which showed a high degree of homology to other bacterial GroES and GroEL proteins. The genes were clustered in the transcription order groES-groEL. Northern blot analyses suggested that the groESL operon is transcribed as a bicistronic 2.2-kb mRNA, the steady-state level of which was markedly increased by temperature elevation. Primer extension analysis demonstrated one potential transcription start site preceding the groESL operon, which is located 100 bp upstream of the groES start codon. The transcription start site was preceded by a putative promoter region highly homologous to the consensus sequences of Escherichia coli sigma 32-type heat shock promoter, which functioned under both normal and heat shock conditions in E. coli. Heat shock mRNA was maximally produced by Methylovorus sp. strain SS1 approximately 10 min after increasing the temperature from 30 to 42 degrees C. The groESL operon was also induced by hydrogen peroxide or salt shock.

Evidence that the fully assembled capsid of Leishmania RNA virus 1-4 possesses catalytically active endoribonuclease activity.

In this study, Leishmania RNA virus 1-4 (LRV1-4) particles purified from host Leishmania guyanensis promastigotes were examined for capsid endoribonuclease. Temperature optimum for the endoribonuclease activity was found to be at 37(O)C to 42(O)C and the activity was specifically inhibited by the aminoglycoside antibiotics, neomycin, kanamycin, and hygromycin and by 100 mM levels of NaCl or KCl. To determine the catalytic domain of the capsid endoribonuclease activity, three point-mutation at cysteine residues at C47S (P1), C128/ 133S (P2), and C194R (P3) were prepared and each gene was constructed into baculoviruses and expressed in Sf9 insect cells. LRV1-4 capsid N- terminus (N2 and N3) and C-terminus (C1 and C2) deletion mutants (Cadd et al., 1994) were also examined by in vitro RNA cleavage assay. The results showed that the capsid mutants; C1, C2, N3, P1, and P2 were capable of forming proper virus-like particles (VLPs) and they all possessed the specific endoribonuclease activity. However, two assembly-defective capsid mutants, N2 (N- terminus 24-amino acids deletion) and P3 mutants, did not retain the specific endoribonuclease activity. Taken together, the results suggest that at least 24 amino acids from the N-terminal region and C194 residue in LRV1-4 capsid protein are functionally important for LRV1-4 viral assembly and the capsid endoribonuclease activity may be dependent upon the properly assembled LRV1-4 virus particles.

Purification, characterization, and physiological response of a catalase-peroxidase in Mycobacterium sp. strain JC1 DSM 3803 grown on methanol.

A novel catalase-peroxidase (CP) from methanol-grown cells of Mycobacterium sp. strain JC1 was purified. The CP exhibited properties of both typical mycobacterial CPs (i.e. strict pH optimum, labile to heat treatment, capable of oxidizing NADH, and resistant to inhibition by 3-amino-1,2,4-triazole) and true catalases (i.e. stable against ethanol-chloroform treatment). The enzyme oxidized methanol and shared common antigenic groups with other mycobacteria. Isoniazid had almost no effect on the growth and expression of CP but inhibited the enzyme activity to some extent. Sodium nitroprusside arrested the growth but strongly stimulated the expression of CP with a concomitant increase in activity after the mid-exponential growth phase.

Purification and some properties of a blue copper protein from Methylobacillus sp. strain SK1 DSM 8269.

A blue protein was purified from the Methylobacillus sp. strain SK1 that is grown on methanol in the presence of copper ion. This protein was found to be a monomer with a molecular weight of 13,500. The Isoelectric point of the protein was estimated to be 8.8. The spectrum of the protein that was treated with ferricyanide showed a broad peak around 620 nm, but that of the dithionite-treated protein revealed no peaks. It contained 0.83 mol of EDTA-stable copper per mol protein. Under air, the protein accelerated the inactivation of methanol dehydrogenase (MDH). The protein was reducible by phenazine methosulfate or by active MDH that was prepared from cells that were grown in the absence of added copper, but not by methanol, dichlorophenol indophenol, or inactive MDH that was prepared from cells that were grown in the presence of added copper. It was also reducible by active MDH in the presence of methanol. The absorption peak at 340 nm of the active MDH disappeared after the enzyme was treated with ferricyanide, hydrogen peroxide, or the purified blue protein. The inactive MDH also showed no peak at 340 nm. The 340-nm peak was not recovered after incubation of the inactive MDH and blue protein-treated active MDH with dithionite or methanol. The inactive MDH and blue protein-treated active MDH co-migrated with the active MDH preparation on nondenaturing polyacrylamide gel, and contained two non-identical subunits with molecular weights that were identical to those of the active MDH. The N-terminal amino acid sequence of the protein was Ala-Gly-Cys-Ser-Val-Asp-Val-Glu-Ala-Asn-Asp-Ala-Met-Gln-Phe. An analysis of the amino acid composition revealed that the protein contained no tryptophan. It contained three cysteines per mol protein. The blue protein in Methylobacillus sp. strain SK1 was produced only in the cells that were grown in the copper-supplemented medium.

Cloning, molecular characterization, and transcriptional analysis of dnaK operon in a methylotrophic bacterium Methylovorus sp. strain SS1 DSM 11726.

Three structural genes that consist of a dnaK operon in a restricted facultative methylotrophic bacterium Methylovorus sp. strain SS1 DSM 11726 were cloned and characterized. The genes were clustered in the transcription order grpE-dnaK-dnaJ. The cloned grpE, dnaK, and dnaJ genes had open-reading frames of 474, 1,926, and 1,116 nucleotides, coding for proteins with calculated molecular masses of 17,390, 69,761, and 41,050, respectively. The overall identities in the deduced amino acid sequences of GrpE, DnaK, and DnaJ with those of the Escherichia coli homologs were 45.2, 74.5, and 61.2%, respectively. Northern blot analyses with grpE-, dnaK-, and dnaJ-specific probes revealed that the three genes are co-transcribed as a 4.0-kb mRNA. A primer extension analysis revealed that the transcription of the dnaK operon started at the nucleotide A that is located 28 bp upstream of the grpE start codon. The transcription start site was preceded by a putative promoter region 15'-CCCCGCTTGAA(13-bp)CCCCAATTT-3'], which is highly homologous to the consensus sequences of the E. coli sigma32-type heat shock promoter. The putative promoter worked under both normal and heat shock conditions in E. coli. The nature of the nucleotide sequence in the second half of the -35 region played a critical role during transcription. The heat shock mRNA was maximally produced at about 10 min after transfer of the Methylovorus sp. strain SS1 from 30 to 42 degrees C. The dnaK operon was also induced by ethanol, hydrogen peroxide, and NaCl shocks. The cloned dnaK operon complemented the E. coli dnaK mutant.

Simple and rapid discrimination of embB codon 306 mutations in Mycobacterium tuberculosis clinical isolates by a real-time PCR assay using an LNA-TaqMan probe.

Single nucleotide polymorphisms in the codon 306 of embB gene are most frequently reported in ethambutol-resistant Mycobacterium tuberculosis clinical isolates. Here, we report a simple and rapid real-time PCR assay using a locked nucleic acid (LNA)-TaqMan probe for discriminating the embB306 mutations. The use of a 15-bp chimeric LNA/DNA probe led to a relatively higher level of sensitivity and fluorescence signal in the wild-type embB306 ATG codon. Therefore, the mutant alleles were easily distinguishable from the wild-type allele by their distinctive amplification curve shapes without a melting analysis of the PCR product. This system was fast and less than 0.1 pg of genomic DNA per reaction was needed for detection. Because the results from this real-time assay were absolutely consistent with those from DNA sequencing, it can be effectively applied as a simple and rapid method for primary screening of embB306 mutations that occur frequently in ethambutol-resistant and/or multidrug-resistant M. tuberculosis isolates.

Molecular characterization of drug-resistant and -susceptible Mycobacterium tuberculosis isolated from patients with tuberculosis in Korea.

We investigated the causal relationship between genotype and phenotype of drug-resistant Mycobacterium tuberculosis isolates obtained from patients with pulmonary tuberculosis (TB) in Korea. Of 80 isolates tested, 17, 20, 1, and 7 isolates were mono-resistant to ethambutol (EMB), isoniazid (INH), pyrazinamide (PZA), and rifampicin (RFP), respectively, and 31 isolates (38.8%) were multidrug-resistant (MDR). Sequencing analysis showed that 78% (32/41) of RFP-resistant strains had mutations in the rifampicin resistance-determining region (RRDR) of rpoB, and the mutation at rpoB531 (59.4%) was most abundant. In 52 INH-resistant strains, mutations were found mostly at C-15T (n = 21, 40.4%) in the inhA promoter region as well as at katG315 (n = 12, 23.1%). Mutations at embB306 were mostly found in 26.7% (12/45) of EMB-resistant isolates. New mutations found here in MDR isolates include rpoB523 (Gly523Glu) and embB319 (Tyr319Ser). Consequently, mutations in the rpoB531, C-15T in the inhA promoter region, embB306, and katG315 would be a useful marker for rapid detection of MDR M. tuberculosis isolates in Korea.

Molecular cloning, purification, and characterization of a superoxide dismutase from a fast-growing Mycobacterium sp. Strain JC1 DSM 3803.

A cytosolic superoxide dismutase (SOD) was purified and characterized from a fast-growing Mycobacterium sp. strain JC1 DSM 3803 grown on methanol. The native molecular weight of the purified SOD was estimated to be 48 kDa. SDS-PAGE revealed a subunit of 23 kDa, indicating that the enzyme is a homodimer. The enzyme activity was inhibited by H(2)O(2) and azide. The purified SOD contained 1.12 and 0.56 g-atom of Mn and Fe per mol of enzyme, respectively, suggesting that it may be a Fe/Mn cambialistic SOD. The apo-SOD reconstitution study revealed that Mn salts were more specific than Fe salts in the SOD activity. The gene encoding the SOD was identified from the JC1 cosmid genomic library by PCR screening protocol. The cloned gene, sodA, had an open reading frame (ORF) of 624 nt, encoding a protein with a calculated molecular weight of 22,930 Da and pi of 5.33. The deduced SodA sequence exhibited 97.6% identity with that of Mycobacterium fortuitum Mn-SOD and clustered with other mycobacterial Mn-SODs. A webtool analysis on the basis of SOD sequence and structure homologies predicted the SOD as a tetrameric Mn-SOD, suggesting that the protein is a dimeric Mn-SOD having tetramer-specific sequence and structure characteristics.

Cloning, expression and characterization of the catalase-peroxidase (KatG) gene from a fast-growing Mycobacterium sp. strain JC1 DSM 3803.

The gene encoding a catalase-peroxidase (KatG) was cloned from chromosomal DNA of a fast-growing Mycobacterium sp. strain JC1 DSM 3803. The nucleotide sequence of a 5.7 kb EcoRI fragment containing the katG and its flanking regions was determined. The fragment (5,706 bps) contained two complete open reading frames (ORFs) encoding putative ferric uptake regulator A (FurA) and KatG proteins. The cloned gene, katG, had an ORF of 2241 nt, encoding a protein with calculated molecular mass of 81,748 Da. The furA was located in the upstream of the katG with the same transcriptional direction and there was a 38 bp gap space between them. The deduced KatG and FurA protein sequences showed significant homologies to KatG2 and Fur2 of Mycobacterium smegmatis and clustered with other mycobacterial KatG and Fur-like proteins in phylogenetic trees, respectively. The recombinant KatG overproduced in Escherichia coli was nearly indistinguishable from the native JC1 catalase-peroxidase in enzymatic properties and also possessed the resistance to organic solvents, indicating that the cloned katG truly encodes the Mycobacterium sp. JC1 catalase-peroxidase. Difference spectroscopy revealed Mn(II) binding near the haem of the KatG. Transcript analysis of the furA-katG using RT-PCR suggests that the katG is independently transcribed from the furA.

Protection against lethal challenge by Ebola virus-like particles produced in insect cells.

Ebola virus-like particles (VLPs) were produced in insect cells using a recombinant baculovirus expression system and their efficacy for protection against Ebola virus infection was investigated. Two immunizations with 50 microg Ebola VLPs (high dose) induced a high level of antibodies against Ebola GP that exhibited strong neutralizing activity against GP-mediated virus infection and conferred complete protection of vaccinated mice against lethal challenge by a high dose of mouse-adapted Ebola virus. In contrast, two immunizations with 10 microg Ebola VLPs (low dose) induced 5-fold lower levels of antibodies against GP and these mice were not protected against lethal Ebola virus challenge, similar to control mice that were immunized with 50 microg SIV Gag VLPs. However, the antibody responses against GP were boosted significantly after a third immunization with 10 microg Ebola VLPs to similar levels as those induced by two immunizations with 50 microg Ebola VLPs, and vaccinated mice were also effectively protected against lethal Ebola virus challenge. Furthermore, serum viremia levels in protected mice were either below the level of detection or significantly lower compared to the viremia levels in control mice. These results show that effective protection can be achieved by immunization with Ebola VLPs produced in insect cells, which give high production yields, and lend further support to their development as an effective vaccine strategy against Ebola virus.