[Show abstract][Hide abstract] ABSTRACT: Background:
The male gamete fertilization factor P48/45 in malaria parasites is a prime transmission-blocking vaccine (TBV) candidate. Efforts to develop antimalarial vaccines are often thwarted by genetic diversity of the target antigens. Here we evaluated the genetic diversity of Pvs48/45 gene in global Plasmodium vivax populations.
We determined 200 Pvs48/45 sequences collected from temperate and subtropical parasite populations in China. Population genetic and evolutionary analyses were performed to determine the levels of genetic diversity, potential signature of selection, and population differentiation.
Analysis of the Pvs48/45 sequences from 200 P. vivax parasites collected in a temperate and a tropical region revealed a low level of genetic diversity (π = 0.0012) with 14 single nucleotide polymorphisms, of which 11 were nonsynonymous. Analysis of 344 Pvs48/45 sequences from nine worldwide P. vivax populations detected a total of 38 haplotypes, of which 13 haplotypes were present only once. Multiple tests for selection confirmed a signature of positive selection on Pvs48/45 with selection skewed to the second cysteine domain. Haplotype network analysis and Wright's fixation index showed large geographical differentiation with the presence of continent-or region-specific mutations in this gene.
Pvs48/45 displays low levels of genetic diversity with the presence of region-specific mutations. Some of the mutations may be potential epitope targets based on their positions in the predicted structure, highlighting the need for future evaluation of these mutations in designing Pvs48/45-based TBV.
Preview · Article · Dec 2015 · Parasites & Vectors
[Show abstract][Hide abstract] ABSTRACT: The host immune response to parasitic infections plays an important role in controlling multiplication of the parasite and reducing clinical symptoms and life-threatening complications. Nitric oxide (NO), an important innate immune factor and classic Th1 immune effector, may play a role in inhibiting plasmodium infection. In this study, we used two different approaches (L-Arginine [precursor of NO] and NOC5 [short-time NO donor]) to prove the roles of NO in malaria infection. We used 6-8 week-old female BALB/c mice infected with the rodent malaria Plasmodium yoelii Landau, Michel et Adam, 1968 - strain 17XL (P.y17XL) as a model. For L-Arg treatment, mice were administered with an oral dose of 1.5 mg/g L-Arg daily for seven consecutive days prior to infection with Py17XL. L-Arg pretreatment resulted in the decrease of the mRNA level of the apical membrane antigen 1 (AMA1) gene, which encodes a protein involved in host invasion. For NOC5 treatment, NOC5 was injected intraperitoneally into the P.y17XL infected mice on day 5 post-infection or incubated in vitro with purified Py17XL schizonts. Both in vivo and in vitro treatments with NOC5 led to down-regulation of the transcript and protein levels of invasion-related molecules (AMA1, merozoites surface protein 1 and Py235). Our results confirmed the protective role of NO in the asexual blood stage of parasitic infection, which may be partially due to reduced expression of parasite invasion molecules.
[Show abstract][Hide abstract] ABSTRACT: Malaria infections display variation patterns of clinical course and outcome. Although CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells play an essential role in immune homeostasis, the immune regulatory roles involved in malaria infection remains to be elucidated. Herein, we compared the disparity in Treg cells response during the course of blood stage Plasmodium chabaudi chabaudi AS (P. c chabaudi AS) infection in DBA/2 and BALB/c mice. BALB/c mice initiated a Th1/Th2 profile respond to P. c chabaudi AS infection, but DBA/2 mice failed to control P. c chabaudi AS infection and almost of them died post-peak parasitemia. At the peak parasitemia, we found that higher proportion of Treg cells with elevated Foxp3 expression in DBA/2 than in BALB/c mice. We used anti-CD25 mAb to deplete Treg cells and found that the survival time and rate were prolonged in DBA/2 mice treated with anti-CD25 mAb. Treatment with anti-CD25 mAb in vivo led to enhanced pro-inflammation responses and Foxp3 expression decline on Treg cells. In contrast, after DBA/2 was treatment with anti-IL-10R mAb, IL-10R blockade in vivo caused excessive pro-inflammation responses and Foxp3 expression loss on CD4(+)CD25(+) T cells. Earlier death was found in all of DBA/2 mice with anti-IL-10R mAb. It suggested that IL-2 and IL-10 signal involved in maintaining Foxp3 expression on Treg cells. In all, the moderate suppressive activity of Treg cells may facilitate resistance to P. c chabaudi AS infection.
No preview · Article · Aug 2012 · Parasitology International
[Show abstract][Hide abstract] ABSTRACT: Transmission-blocking vaccines (TBVs) have been considered an important strategy for disrupting the malaria transmission cycle, especially for Plasmodium vivax malaria, which undergoes gametocytogenesis earlier during infection. Pvs25 and Pvs28 are transmission-blocking vaccine candidates for P. vivax malaria. Assessment of genetic diversity of the vaccine candidates will provide necessary information for predicting the performance of vaccines, which will guide us during the development of malaria vaccines.
We sequenced the coding regions of pvs25 and pvs28 from 30 P. vivax isolates from Yunnan Province, identifying five amino acid haplotypes of Pvs25 and seven amino acid haplotypes of Pvs28. Among a total of four mutant residues, the predominant haplotype of Pvs25 only had the I130T substitution. For Pvs28, a total of eight amino acid substitutions were identified. The predominant haplotype of Pvs28 had two substitution at positions 52 (M52L) and 140 (T140S) with 5-6 GSGGE/D tandem repeats at the end of fourth EGF-like domain. Most amino acid substitutions were common with previous reports from South Asian isolates. Although the nucleotide diversity of pvs28 (π = 0.0034 ± 0.0012) was significantly higher than pvs25 (π = 0.0013 ± 0.0009), it was still conserved when compared with the blood stage vaccine candidates.
Genetic analysis revealed limited genetic diversity of pvs25 and pvs28, suggesting antigenic diversity may not be a particular problem for Sal I based TBVs in most P. vivax-endemic areas of China.
Full-text · Article · Nov 2011 · Parasites & Vectors
[Show abstract][Hide abstract] ABSTRACT: The outcome of Plasmodium yoelii 17XL (P.y17XL)-infected BALB/c and DBA/2 mice, ranging from death to spontaneous cure, depends largely on the establishment of effective Th1 and Th2 responses and a successful switch between Th1 and Th2 responses, as well as appropriate functioning of CD4(+)CD25(+)Foxp3(+)regulatory T cells (Tregs). The infection with another malaria-causing parasite, Plasmodium chabaudi AS (P.cAS), leads to a different outcome in BALB/c and DBA/2 mice compared to mice infected with P.y17XL alone. To understand the consequence of co-infection with P.y17XL and P.cAS, we determined the proliferation curve of parasites, pro-inflammatory/anti-inflammatory cytokine profiles, and the dynamic changes of the number of Tregs in DBA/2 and BALB/c mice with single or mixed-species infections. The infective mode in mixed-species infections was the same as single P.y17XL infections. The multiplication of P.y17XL parasites prevailed in BALB/c and DBA/2 mice with early mixed infections, as detected by RTQ-PCR. Subsequently, the multiplication of P.cAS parasites dominated in DBA/2 mice with mixed infections, while BALB/c mice succumbed to infection. In addition, the dynamic changes in IFN-gamma and IL-4 production in mice with mixed infections, used as a measure of Th1 and Th2 responsiveness, were consistent with P.y17XL-infected mice. Treg activation and the IL-10 level were also closely related to susceptibility to infection. Our findings demonstrate that the characteristics of the immune response during infections with mixed species are dependent on the mode of proliferation of different species of Plasmodium. Indeed, different species of Plasmodium can influence each other in the same host.
No preview · Article · Sep 2010 · Parasitology International
[Show abstract][Hide abstract] ABSTRACT: Protective immunity against murine malaria infection depends largely on the establishment of effective Th1 immune response during the early stages of infection. Experimental data suggest that the death of Plasmodium yoelii 17XL (Py 17XL) susceptible BALB/c mice results from the suppression of Th1 immune response mediated by CD4+CD25+Foxp3+ regulatory T cells (Tregs). However, the mechanism by which Tregs regulate Th1 immune response is poorly understood. Since immunity is initiated by dendritic cells (DCs), we analysed DC responses to Py 17XL in control and Treg-depleted BALB/c mice. Myeloid DC proliferation, phenotypic maturation and interleukin-12 (IL-12) production were strongly inhibited in control BALB/c mice. In contrast, plasmacytoid DC proliferation and IL-10 production were strongly enhanced in control BALB/c mice. In-vivo depletion of Tregs resulted in significantly reversed inhibition of DC response, which may contribute to the establishment of Th1 immune response, indicating that Tregs contribute to the suppression of Th1 immune response during malaria. These findings suggest Tregs contribute to prevent Th1 immune response establishment during the early stage of Py 17XL infection by inhibiting DC response.
Preview · Article · Dec 2009 · Folia parasitologica
[Show abstract][Hide abstract] ABSTRACT: The outcome of Plasmodium yoelii 17XL-infected BALB/c and DBA/2 mice, ranging from death to spontaneous cure, respectively, depends largely on the establishment of effective pro-inflammatory type 1 responses during the early stages of infection and associates with CD4(+)CD25(+)Foxp3(+)regulatory T cells (Tregs). Here, effects of Tregs were analysed on early P. yoelii 17XL infection in BALB/c and DBA/2 mice. In vivo depletion of Tregs significantly reversed the inhibited establishment of effective pro-inflammatory type 1 responses in BALB/c mice, indicating that this cell population contributed to the suppression of T-cell function in malaria. Moreover, the proportion and absolute numbers of IL-10-secreting Tregs in BALB/c mice were significantly higher than that found in DBA/2 mice by intracytoplasmic staining, and IL-10 production was correlated with the Tregs population. In addition, in vivo Tregs depletion decreased the production of IL-10 and the apoptosis of CD4+ T cells. Consistently, IL-10R blockade also had the same effect as that of Tregs depletion in P. yoelii 17XL-infected BALB/c mice. Our data demonstrate that Tregs perhaps have an important role in regulating pro-inflammatory type 1 responses in an IL-10-dependent manner and induce CD4+ T cell apoptosis during the early stage of P. yoelii 17XL infection.
[Show abstract][Hide abstract] ABSTRACT: The effect of antimalarial drugs on immune responses to the malaria infection is evaluated in vivo using two experimental self-cured rodent models. BALB/c and DBA/2 mice were infected by Plasmodium yoelii 17XNL and 17XL strains, respectively, and then treated with different doses of antimalarial drugs: chloroquine (228mg/kg or 114mg/kg of the body weight) or artesunate (78mg/kg or 39mg/kg). The effect of antimalarial drugs on host immune responses was evaluated by parasitemia, splenocyte IFN-gamma production level, and parasite-specific IgG level in the serum, however, no significant differences were observed between drug-treated and untreated groups. Moreover, most of the infected mice of all groups showed the ability to resist homologous reinfection (challenged on day 60 post-infection), only a few mice experienced transient, low parasitemia. The rechallenged mice were accompanied by high level of parasite-specific IgG. Therefore, this research implicated that, for BALB/c and DBA/2 mice, chloroquine or artesunate treatment of blood-stage P. yoelii infections does not compromise acquired immunity to malaria in either primary infection or upon rechallenge.
Full-text · Article · Aug 2007 · Experimental Parasitology
[Show abstract][Hide abstract] ABSTRACT: To observe the effect of nitric oxide (NO) on exflagellation of malaria parasite.
The level of parasitemia and gametocytaemia in DBA/2 mice infected with Plasmodium yoelii 17XL was measured by scanning Giemsa-stained blood smears, and the NO level in culture supernatant of splenocytes was checked using Griess reaction. The mice were injected with different doses of NO donor (NOC5) on day 4 post-infection, and control mice were injected with NOC5 precursor. On day 6 post-infection, mice were injected with NOS inhibitor (L-NMMA), and control mice were injected with D-NMMA and PBS, respectively. Blood samples were collected from tail vein of mice before injection, 30 and 60 min after being injected with NOC5 and NOC5 precursor, 4 and 8 h after being injected with L-NMMA, D-NMMA, and PBS respectively. Exflagellation number of gametocytes in blood culture was counted under microscope. Results The NO level in culture supernatant of splenocytes from mice on day 4 and 6 post-infection was 16.5 mmol/L and 30.4 mmol/L, and exflagellation number was 11.33 and 0.66, respectively. The number of exflagellation in parasitized erythrocytes, obtained from mice on day 4 post-infection, was 5.33 and 2.66, respectively, 30 and 60 min after injection of 1 mg NO donor (NOC5), significantly lower than that of the control (P<0.01). The number of exflagellation in parasitized erythrocytes derived from mice on day 6 post-infection was 1.83, 8 h after the injection of NOS inhibitor (L-NMMA), which was significantly higher than that of the control (P<0.01).
NO is a major effector molecule resulting in natural transmission-blocking of malaria parasite by directly inhibiting exflagellation of male gametocytes.
No preview · Article · Jul 2007 · Zhongguo ji sheng chong xue yu ji sheng chong bing za zhi = Chinese journal of parasitology & parasitic diseases
[Show abstract][Hide abstract] ABSTRACT: The outcome of experimental murine infection with different strains of malaria parasites, ranging from spontaneous cure to death, depends largely on the establishment of effective Th1 responses during the early stages of infection. Here we describe the disparity in CD4(+)CD25(+) regulatory T cell (Treg) responses during the early stages of infection with the highly virulent Plasmodium yoelii 17XL strain in susceptible (BALB/c) and resistant (DBA/2) mice. An increased proportion of Tregs 3-4 days post inoculation, co-occurring with elevated IL-10 levels, is observed in BALB/c but not in DBA/2 mice. These findings suggest that Treg proliferation might be causally associated with the suppression of Th1 responses during early malaria infection, leading to increase parasitemia and mortality in BALB/c mice, possibly in an IL-10-dependent manner.