Biomedical subjects

Maria M Mota

Publications and source records attributed to Maria M Mota.

18 recordsLinked to original sources

PubMed2006

Infection by and protective immune responses against Plasmodium berghei ANKA are not affected in macrophage scavenger receptors A deficient mice.

BACKGROUND: Scavenger receptors (SRs) recognize endogenous molecules modified by pathological processes as well as components of diverse microorganisms. Mice deficient for both SR-AI and II are more susceptible to infections by a variety of bacterial and viral pathogens. RESULTS: Here we show that SR-A deficient mice and wild type mice are equally susceptible to malaria infection both during liver and blood stages. Moreover, like wild type mice, SR-A deficient mice are able to mount a protective immune response against radiation attenuated sporozoites. CONCLUSION: Our results do not reveal a function of SR-A I and II receptors in the Plasmodium berghei ANKA infection, both in the development of CM and parasitemia control. Moreover, these receptors appear not to be required for the establishment of a protective immune response against the malaria liver stages.

Animals↗

PubMed2006

Improved transfection and new selectable markers for the rodent malaria parasite Plasmodium yoelii.

The rodent malaria Plasmodium yoelii is a useful model to study protective immunity to pre-erythrocytic stages of infection, pathogenesis of erythrocytic stages, and vaccine development. However, the utility of the P. yoelii model system has not been fully realized because transfection and genetic manipulation methodologies for this rodent species are less developed than that of another rodent species Plasmodium berghei. Here we report improved transfection efficiency using the AMAXA nucleofector system compared to conventional transfection methodologies. We also show that heterologous promoters from P. berghei can be used to drive expression of a green fluorescent protein (GFP) reporter protein in P. yoelii. In an effort to develop additional selectable markers for this parasite, we also tested positive selectable markers that have been used successfully in P. falciparum and P. berghei. Human dihydrofolate reductase (hdhfr) and Toxoplasma gondii dihydrofolate reductase-thymidylate synthase (Tgdhfr-ts) conferred drug resistance to WR99210 and pyrimethamine, respectively, when introduced as episomes. These improvements should make genetic manipulation of P. yoelii more amenable and facilitate further studies of host-parasite interactions using this attractive rodent model.

Animals↗

PubMed2006

Antimalarial drugs - host targets (re)visited.

Every year, forty percent of the world population is at risk of contracting malaria. Hopes for the erradication of this disease during the 20th century were dashed by the ability of Plasmodium falciparum, its most deadly causative agent, to develop resistance to available drugs. Efforts to produce an effective vaccine have so far been unsuccessful, enhancing the need to develop novel antimalarial drugs. In this review, we summarize our knowledge concerning existing antimalarials, mechanisms of drug-resistance development, the use of drug combination strategies and the quest for novel anti-plasmodial compounds. We emphasize the potential role of host genes and molecules as novel targets for newly developed drugs. Recent results from our laboratory have shown Hepatocyte Growth Factor/MET signaling to be essential for the establishment of infection in hepatocytes. We discuss the potential use of this pathway in the prophylaxis of malaria infection.

Animals↗

PubMed2006

The silent path to thousands of merozoites: the Plasmodium liver stage.

Plasmodium sporozoites are deposited in the skin of their vertebrate hosts through the bite of an infected female Anopheles mosquito. Most of these parasites find a blood vessel and travel in the peripheral blood circulation until they reach the liver sinusoids. Once there, the sporozoites cross the sinusoidal wall and migrate through several hepatocytes before they infect a final hepatocyte, with the formation of a parasitophorous vacuole, in which the intrahepatic form of the parasite grows and multiplies. During this period, each sporozoite generates thousands of merozoites. As the development of Plasmodium sporozoites inside hepatocytes is an obligatory step before the onset of disease, understanding the parasite's requirements during this period is crucial for the development of any form of early intervention. This Review summarizes our current knowledge on this stage of the Plasmodium life cycle.

Animals↗

PubMed2006

Be in motion . . .

Most Apicomplexan are obligate intracellular parasites and at different steps of their life cycle they invade host cells. The invasive forms are generally called zoites and the majority of them largely depend on a unique form of gliding motility to invade cells. Although the parasite intracellular motor complex that drives gliding motility and/or invasion is shared across different parasite stages and species, the extracellular transmembrane adhesins required to recognize and bind host molecules are not only species- but also stage-specific (even if homologues). This is not such a surprise as different parasite stages interact with different hosts or distinct host cells. In this issue, Siden-Kiamos et al. shows that specificity extends into the parasite cell, affecting how motility is regulated. Why is specificity occurring at this level? And how important is it? These are critical issues that will be hopefully addressed in the near future.

Animals↗

PubMed2005

Genetically attenuated, P36p-deficient malarial sporozoites induce protective immunity and apoptosis of infected liver cells.

Immunization with Plasmodium sporozoites that have been attenuated by gamma-irradiation or specific genetic modification can induce protective immunity against subsequent malaria infection. The mechanism of protection is only known for radiation-attenuated sporozoites, involving cell-mediated and humoral immune responses invoked by infected hepatocytes cells that contain long-lived, partially developed parasites. Here we analyzed sporozoites of Plasmodium berghei that are deficient in P36p (p36p(-)), a member of the P48/45 family of surface proteins. P36p plays no role in the ability of sporozoites to infect and traverse hepatocytes, but p36p(-) sporozoites abort during development within the hepatocyte. Immunization with p36p(-) sporozoites results in a protective immunity against subsequent challenge with infectious wild-type sporozoites, another example of a specifically genetically attenuated sporozoite (GAS) conferring protective immunity. Comparison of biological characteristics of p36p(-) sporozoites with radiation-attenuated sporozoites demonstrates that liver cells infected with p36p(-) sporozoites disappear rapidly as a result of apoptosis of host cells that may potentiate the immune response. Such knowledge of the biological characteristics of GAS and their evoked immune responses are essential for further investigation of the utility of an optimized GAS-based malaria vaccine.

Animals↗

PubMed2005

Murine malaria parasite sequestration: CD36 is the major receptor, but cerebral pathology is unlinked to sequestration.

Sequestration of malaria-parasite-infected erythrocytes in the microvasculature of organs is thought to be a significant cause of pathology. Cerebral malaria (CM) is a major complication of Plasmodium falciparum infections, and PfEMP1-mediated sequestration of infected red blood cells has been considered to be the major feature leading to CM-related pathology. We report a system for the real-time in vivo imaging of sequestration using transgenic luciferase-expressing parasites of the rodent malaria parasite Plasmodium berghei. These studies revealed that: (i) as expected, lung tissue is a major site, but, unexpectedly, adipose tissue contributes significantly to sequestration, and (ii) the class II scavenger-receptor CD36 to which PfEMP1 can bind is also the major receptor for P. berghei sequestration, indicating a role for alternative parasite ligands, because orthologues of PfEMP1 are absent from rodent malaria parasites, and, importantly, (iii) cerebral complications still develop in the absence of CD36-mediated sequestration, dissociating parasite sequestration from CM-associated pathology. Real-time in vivo imaging of parasitic processes may be used to evaluate the molecular basis of pathology and develop strategies to prevent pathology.

Adipose Tissue↗

PubMed2005

Apoptotic Plasmodium-infected hepatocytes provide antigens to liver dendritic cells.

Malaria starts with infection of the host liver by Plasmodium sporozoites. Inoculation with radiation-attenuated Plasmodium sporozoites induces complete protection against malaria. Protection is mediated by dendritic cells (DCs) and CD8(+) T cells, but the source of parasite antigens mediating this response remains unclear. Here, we show that hepatocytes infected with irradiated Plasmodium sporozoites undergo apoptosis shortly after infection. Infection with irradiated sporozoites induces the recruitment of DCs to the liver, where they phagocytose apoptotic infected hepatocytes containing parasite antigens. We propose that apoptotic Plasmodium-infected hepatocytes provide a source of parasite antigens for the initiation of the protective immune response.

Animals↗

PubMed2005

HGF/MET signalling protects Plasmodium-infected host cells from apoptosis.

Plasmodium, the causative agent of malaria, migrates through several hepatocytes before initiating a malaria infection. We have previously shown that this process induces the secretion of hepatocyte growth factor (HGF) by traversed cells, which renders neighbour hepatocytes susceptible to infection. The signalling initiated by HGF through its receptor MET has multifunctional effects on various cell types. Our results reveal a major role for apoptosis protection of host cells by HGF/MET signalling on the host susceptibility to infection. Inhibition of HGF/MET signalling induces a specific increase in apoptosis of infected cells leading to a great reduction on infection. Since HGF/MET signalling is capable of protecting cells from apoptosis by using both PI3-kinase/Akt and, to a lesser extent, MAPK pathways, we determined the impact of these pathways on Plasmodium sporozoite infection. Although inhibition of either of these pathways leads to a reduction in infection, inhibition of PI3-kinase/Akt pathway caused a stronger effect, which correlated with a higher level of apoptosis in infected host cells. Altogether, the results show that the HGF/MET signalling requirement for infection is mediated by its anti-apoptotic signal effects. These results demonstrate for the first time that active inhibition of apoptosis in host cell during infection by Plasmodium is required for a successful infection.

Animals↗

PubMed2004

Plasmodium berghei parasite transformed with green fluorescent protein for screening blood schizontocidal agents.

High priority has been given to new assays that facilitate and accelerate the development of novel antimalarial compounds. Unlike evaluation of drugs in vitro, in which new approaches have been used to expedite identification of parasites, the conventional in vivo murine assay requires determination of parasitemia by light microscopy, an incompatible technique to test large numbers of drugs. We have investigated the possibility of using an autonomously fluorescent Plasmodium berghei strain, stably transformed with the green fluorescent protein, to rapidly quantify parasite growth by flow cytometry. The major improvement of this method is that P. berghei line transformed with green fluorescent protein parasites can be quickly and specifically detected in a drop of parasite-infected blood without any manipulation of the sample. Our results showed a clear correlation between the numbers of fluorescent cells detected by flow cytometry and conventional parasitemia, including a correspondence in the peaks of parasitemia. The validation of P. berghei line transformed with green fluorescent protein for chemotherapy studies was performed by evaluating its response to conventional antimalarial drugs such as chloroquine, quinine and sodium artesunate. The results of drug-susceptibility assays as determined by flow cytometry were comparable with those obtained by microscopic examination of Giemsa-stained slides. This PbGFP parasite should prove to be a rapid, simple and sensitive tool for the examination of the large number of compounds and conditions involved in the initial stages of drug development.

Animals↗

PubMed2004

Targeting Plasmodium host cells: survival within hepatocytes.

Upon entering their host, Plasmodium sporozoites travel directly to the liver. Once there, they migrate through several hepatocytes before they infect a final one. During migration, sporozoites breach the plasma membrane of traversed hepatocytes, but to infect they must form a parasitophorous vacuole, in which the intra-hepatic form of the parasite grows and multiplies. During this period there is a remarkable parasite multiplication, but little is known about the requirements and strategies that are developed to be successful. Hepatocyte growth factor and its receptor on hepatocytes might enhance early Plasmodium development within these cells. We anticipate that this might be the basis for further studies on host-cell requirements for Plasmodium development.

Animals↗

PubMed2004

Survival of protozoan intracellular parasites in host cells.

The most common human diseases are caused by pathogens. Several of these microorganisms have developed efficient ways in which to exploit host molecules, along with molecular pathways to ensure their survival, differentiation and replication in host cells. Although the contribution of the host cell to the development of many intracellular pathogens (particularly viruses and bacteria) has been unequivocally established, the study of host-cell requirements during the life cycle of protozoan parasites is still in its infancy. In this review, we aim to provide some insight into the manipulation of the host cell by parasites through discussing the hurdles that are faced by the latter during infection.

Animals↗

PubMed2004

Migration through host cells: the first steps of Plasmodium sporozoites in the mammalian host.

Malaria starts with the infection of the liver by Plasmodium sporozoites. This form of the parasite migrates through several host cells breaching their plasma membranes before infecting a final hepatocyte which they enter forming a parasitophorous vacuole. It is still controversial why Plasmodium sporozoites migrate through host cells. By reviewing the most recent literature, we hope to give an insight on the different steps of host invasion in which migration through cells is involved and on the possible role for this mechanism in infection.

Animals↗

PubMed2003

Hepatocyte growth factor and its receptor are required for malaria infection.

Plasmodium, the causative agent of malaria, must first infect hepatocytes to initiate a mammalian infection. Sporozoites migrate through several hepatocytes, by breaching their plasma membranes, before infection is finally established in one of them. Here we show that wounding of hepatocytes by sporozoite migration induces the secretion of hepatocyte growth factor (HGF), which renders hepatocytes susceptible to infection. Infection depends on activation of the HGF receptor, MET, by secreted HGF. The malaria parasite exploits MET not as a primary binding site, but as a mediator of signals that make the host cell susceptible to infection. HGF/MET signaling induces rearrangements of the host-cell actin cytoskeleton that are required for the early development of the parasites within hepatocytes. Our findings identify HGF and MET as potential targets for new approaches to malaria prevention.

Actins↗

PubMed2003

Malaria blood stage suppression of liver stage immunity by dendritic cells.

Malaria starts with Plasmodium sporozoites infection of the host's liver, where development into blood stage parasites occurs. It is not clear why natural infections do not induce protection against the initial liver stage and generate low CD8+ T cell responses. Using a rodent malaria model, we show that Plasmodium blood stage infection suppresses CD8+ T cell immune responses that were induced against the initial liver stage. Blood stage Plasmodium affects dendritic cell (DC) functions, inhibiting maturation and the capacity to initiate immune responses and inverting the interleukin (IL)-12/IL-10 secretion pattern. The interaction of blood stage parasites with DCs induces the secretion of soluble factors that inhibit the activation of CD8+ T cells in vitro and the suppression of protective CD8+ T cell responses against the liver stage in vivo. We propose that blood stage infection induces DCs to suppress CD8+ T cell responses in natural malaria infections. This evasion mechanism leaves the host unprotected against reinfection by inhibiting the immune response against the initial liver stage of the disease.

Animals↗

PubMed2002

Migration through host cells activates Plasmodium sporozoites for infection.

Plasmodium sporozoites, the infective stage of the malaria parasite transmitted by mosquitoes, migrate through several hepatocytes before infecting a final one. Migration through hepatocytes occurs by breaching their plasma membranes, and final infection takes place with the formation of a vacuole around the sporozoite. Once in the liver, sporozoites have already reached their target cells, making migration through hepatocytes prior to infection seem unnecessary. Here we show that this migration is required for infection of hepatocytes. Migration through host cells, but not passive contact with hepatocytes, induces the exocytosis of sporozoite apical organelles, a prerequisite for infection with formation of a vacuole. Sporozoite activation induced by migration through host cells is an essential step of Plasmodium life cycle.

Animals↗

PubMed2002

PSLAP, a protein with multiple adhesive motifs, is expressed in Plasmodium falciparum gametocytes.

A gene coding for a protein containing two Scavenger Receptor Cysteine-Rich (SRCR) motifs, four Limulus factor C, Coch-5b2 and Lgl1 (LCCL) motifs; and one Polycystin-1, Lipoxygenase and Alpha Toxin (PLAT) motif was cloned from Plasmodium chabaudi and homologues identified in the P. falciparum and P. yoelii genome data bases. At least one of these sequence motifs (SRCR) has adhesive properties in other proteins, therefore, we propose to name this protein PSLAP for Plasmodium SRCR, LCCL Adhesive-like Protein. Southern blotting and chromosome analysis showed that pslap is a single copy gene on chromosome 14 in P. falciparum 3D7. pslap mRNA is strongly expressed in P. falciparum gametocytes, but was undetectable on Northern blots of RNA from the asexual blood stages. Polyclonal antibodies raised to different parts of PSLAP detected a protein expressed in late gametocytes, but not in the early stages of gametocytogenesis or asexual blood stages of P. falciparum. We suggest that PSLAP functions in the mosquito, for example, in modulation of the invertebrate host immune response or in protection against complement factors in the blood meal.

Amino Acid Motifs↗

PubMed2002

Invasion of mammalian host cells by Plasmodium sporozoites.

Malaria is transmitted through the bite of an infected mosquito, which introduces Plasmodium sporozoites into the mammalian host. Sporozoites rapidly reach the liver of the host where they are sequestered, a process probably mediated by circumsporozoite (CS) protein. Once in the liver, sporozoites migrate through several hepatocytes by breaching their plasma membranes before infecting a final hepatocyte with formation of a vacuole around the sporozoite, where development occurs into blood stage parasites. We propose that migration through several host cells activates sporozoites for ultimate productive invasion. This migration triggers sporozoite exocytosis, which is necessary for hepatocyte invasion, probably because it provides molecules, such as thrombospondin-related anonymous protein (TRAP), likely required for sporozoite invasion with the formation of a vacuole. How sporozoites migrate from the skin to the liver and invade hepatocytes remains unclear. Understanding this initial stage of malaria is crucial for the development of new approaches against the disease.

Animals↗