112 research outputs found
Emerging Functions of Transcription Factors in Malaria Parasite
Transcription is a process by which the genetic information stored in DNA is converted into mRNA by enzymes known as RNA polymerase. Bacteria use only one RNA polymerase to transcribe all of its genes while eukaryotes contain three RNA polymerases to transcribe the variety of eukaryotic genes. RNA polymerase also requires other factors/proteins to produce the transcript. These factors generally termed as transcription factors (TFs) are either associated directly with RNA polymerase or add in building the actual transcription apparatus. TFs are the most common tools that our cells use to control gene expression. Plasmodium falciparum is responsible for causing the most lethal form of malaria in humans. It shows most of its characteristics common to eukaryotic transcription but it is assumed that mechanisms of transcriptional control in P. falciparum somehow differ from those of other eukaryotes. In this article we describe the studies on the main TFs such as myb protein, high mobility group protein and ApiA2 family proteins from malaria parasite. These studies show that these TFs are slowly emerging to have defined roles in the regulation of gene expression in the parasite
Membrane destabilization by monomeric hIAPP observed by imaging fluorescence correlation spectroscopy
Monomeric hIAPP significantly destabilizes both model and live cell membranes by increasing membrane fluidity. This interaction with membranes happens via carpet formation followed by lipid extraction in a concentration dependent manner and thus we propose that hIAPP aggregation prior to membrane interaction may not be necessary for its cytotoxicity
Characterization of protective epitopes in a highly conserved Plasmodium falciparum antigenic protein containing repeats of acidic and basic residues
The delineation of putatively protective and immunogenic epitopes in vaccine candidate proteins constitutes a major research effort towards the development of an effective malaria vaccine. By virtue of its role in the formation of the immune clusters of merozoites, its location on the surface of merozoites, and its highly conserved nature both at the nucleotide sequence level and the amino acid sequence level, the antigen which contains repeats of acidic and basic residues (ABRA) of the human malaria parasite Plasmodium falciparum represents such an antigen. Based upon the predicted amino acid sequence of ABRA, we synthesized eight peptides, with six of these (AB-1 to AB-6) ranging from 12 to 18 residues covering the most hydrophilic regions of the protein, and two more peptides (AB-7 and AB-8) representing its repetitive sequences. We found that all eight constructs bound an appreciable amount of antibody in sera from a large proportion of P. falciparum malaria patients; two of these peptides (AB-1 and AB-3) also elicited a strong proliferation response in peripheral blood mononuclear cells from all 11 human subjects recovering from malaria. When used as carrier-free immunogens, six peptides induced a strong, boostable, immunoglobulin G-type antibody response in rabbits, indicating the presence of both B-cell determinants and T-helper-cell epitopes in these six constructs. These antibodies specifically cross-reacted with the parasite protein(s) in an immunoblot and in an immunofluorescence assay. In another immunoblot, rabbit antipeptide sera also recognized recombinant fragments of ABRA expressed in bacteria. More significantly, rabbit antibodies against two constructs (AB-1 and AB-5) inhibited the merozoite reinvasion of human erythrocytes in vitro up to ~90%. These results favor further studies so as to determine possible inclusion of these two constructs in a multicomponent subunit vaccine against asexual blood stages of P. falciparum
A novel Plasmodium falciparum rhoptry associated adhesin mediates erythrocyte invasion through the sialic-acid dependent pathway
Erythrocyte invasion by Plasmodium falciparum merozoites is
central to blood-stage infection and malaria pathogenesis. This
intricate process is coordinated by multiple parasite adhesins
that bind erythrocyte receptors and mediate invasion through
several alternate pathways. P. falciparum expresses 2700 genes
during the blood-stages, of which the identity and function of
many remains unknown. Here, we have identified and characterized
a novel P. falciparum rhoptry associated adhesin (PfRA) that
mediates erythrocyte invasion through the sialic-acid dependent
pathway. PfRA appears to play a significant functional role as
it is conserved across different Plasmodium species. It is
localized in the rhoptries and further translocated to the
merozoite surface. Both native and recombinant PfRA specifically
bound erythrocytes in a sialic-acid dependent, chymotrypsin and
trypsin resistant manner, which was abrogated by PfRA antibodies
confirming a role in erythrocyte invasion. PfRA antibodies
inhibited erythrocyte invasion and in combination with
antibodies against other parasite ligands produced an additive
inhibitory effect, thus validating its important role in
erythrocyte invasion. We have thus identified a novel P.
falciparum adhesin that binds with a sialic acid containing
erythrocyte receptor. Our observations substantiate the strategy
to block P. falciparum erythrocyte invasion by simultaneously
targeting multiple conserved merozoite antigens involved in
alternate invasion pathways
Host age and expression of genes involved in red blood cell invasion in Plasmodium falciparum field isolates
Plasmodium falciparum proteins involved in erythrocyte invasion
are main targets of acquired immunity and important vaccine
candidates. We hypothesized that anti-parasite immunity acquired
upon exposure would limit invasion-related gene (IRG) expression
and affect the clinical impact of the infection. 11 IRG
transcript levels were measured in P. falciparum isolates by
RT-PCR, and IgG/IgM against invasion ligands by Luminex(R), in
50 Mozambican adults, 25 children with severe malaria (SM) and
25 with uncomplicated malaria (UM). IRG expression differences
among groups and associations between IRG expression and
clinical/immunologic parameters were assessed. IRG expression
diversity was higher in parasites infecting children than adults
(p = 0.022). eba140 and ptramp expression decreased with age (p
= 0.003 and 0.007, respectively) whereas p41 expression
increased (p = 0.022). pfrh5 reduction in expression was abrupt
early in life. Parasite density decreased with increasing pfrh5
expression (p < 0.001) and, only in children, parasite
density increased with p41 expression (p = 0.007), and decreased
with eba175 (p = 0.013). Antibody responses and IRG expression
were not associated. In conclusion, IRG expression is associated
with age and parasite density, but not with specific antibody
responses in the acute phase of infection. Our results confirm
the importance of multi-antigen vaccines development to avoid
parasite immune escape when tested in malaria-exposed
individuals
Assessment of the Combined Effect of Epstein-Barr Virus and Plasmodium falciparum Infections on Endemic Burkitt Lymphoma Using a Multiplex Serological Approach
Epstein–Barr virus (EBV) is a necessary cause of endemic Burkitt lymphoma (eBL), while the role of Plasmodium falciparum in eBL remains uncertain. This study aimed to generate new hypotheses on the interplay between both infections in the development of eBL by investigating the IgG and IgM profiles against several EBV and P. falciparum antigens. Serum samples collected in a childhood study in Malawi (2005–2006) from 442 HIV-seronegative children (271 eBL cases and 171 controls) between 1.4 and 15 years old were tested by quantitative suspension array technology against a newly developed multiplex panel combining 4 EBV antigens [Z Epstein–Barr replication activator protein (ZEBRA), early antigen-diffuse component (EA-D), EBV nuclear antigen 1, and viral capsid antigen p18 subunit (VCA-p18)] and 15 P. falciparum antigens selected for their immunogenicity, role in malaria pathogenesis, and presence in different parasite stages. Principal component analyses, multivariate logistic models, and elastic-net regressions were used. As expected, elevated levels of EBV IgG (especially against the lytic antigens ZEBRA, EA-D, and VCA-p18) were strongly associated with eBL [high vs low tertile odds ratio (OR) = 8.67, 95% confidence interval (CI) = 4.81–15.64]. Higher IgG responses to the merozoite surface protein 3 were observed in children with eBL compared with controls (OR = 1.29, 95% CI = 1.02–1.64), showing an additive interaction with EBV IgGs (OR = 10.6, 95% CI = 5.1–22.2, P = 0.05). Using elastic-net regression models, eBL serological profile was further characterized by lower IgM levels against P. falciparum preerythrocytic-stage antigen CelTOS and EBV lytic antigen VCA-p18 compared with controls. In a secondary analysis, abdominal Burkitt lymphoma had lower IgM to EBV and higher IgG to EA-D levels than cases with head involvement. Overall, this exploratory study confirmed the strong role of EBV in eBL and identified differential IgG and IgM patterns to erythrocytic vs preerythrocytic P. falciparum antigens that suggest a more persistent/chronic malaria exposure and a weaker IgM immune response in children with eBL compared with controls. Future studies should continue exploring how the malaria infection status and the immune response to P. falciparum interact with EBV infection in the development of eBL
Identifying Immune Correlates of Protection Against Plasmodium falciparum Through a Novel Approach to Account for Heterogeneity in Malaria Exposure
Background: A main criterion to identify malaria vaccine
candidates is the proof that acquired immunity against them is
associated with protection from disease. The age of the studied
individuals, heterogeneous malaria exposure, and assumption of
the maintenance of a baseline immune response can confound these
associations. Methods: Immunoglobulin G/immunoglobulin M (IgG/
IgM) levels were measured by Luminex(R) in Mozambican children
monitored for clinical malaria from birth until 3 years of age,
together with functional antibodies. Studied candidates were
pre-erythrocytic and erythrocytic antigens, including
EBAs/PfRhs, MSPs, DBLs, and novel antigens merely or not
previously studied in malaria-exposed populations. Cox
regression models were estimated at 9 and 24 months of age,
accounting for heterogeneous malaria exposure or limiting
follow-up according to the antibody's decay. Results:
Associations of antibody responses with higher clinical malaria
risk were avoided when accounting for heterogeneous malaria
exposure or when limiting the follow-up time in the analyses.
Associations with reduced risk of clinical malaria were found
only at 24 months old, but not younger children, for IgG breadth
and levels of IgG targeting EBA140III-V, CyRPA, DBL5epsilon and
DBL3x, together with C1q-fixation activity by antibodies
targeting MSP119. Conclusions: Malaria protection correlates
were identified, only in children aged 24 months old when
accounting for heterogeneous malaria exposure. These results
highlight the relevance of considering age and malaria exposure,
as well as the importance of not assuming the maintenance of a
baseline immune response throughout the follow-up. Results may
be misleading if these factors are not considered
Cross-reactivity between repeat peptides of circumsporozoite proteins (CSPs) of different malaria parasites
Information on the primary sequences of CSP repeat peptides in different malaria parasites is now available. The central third of the CSPs consists of multiple repeating sequences. These repetitive segments are immunodominant epitopes of the CSPs. It has been shown that these repeat units (antigens) cross-react with heterologous peptides (like blood-stage antigens), but so far, no work has been done to show the existence of cross-reactivity between the repeat peptides of different malaria parasites. Using solid phase methodology, we synthesized peptides consisting of repeat units corresponding to four different species of malaria circumsporozoite antigens, namely Plasmodium falciparum (NANP4), P. vivax (DRADGQPAGDRAAGOPAG), P. cynomolgi (AGNNAAGEAGNNAAAGE), P. yeolii (QGPGAP)4. The synthetic peptides were conjugated to bovine serum albumin with glutaraldehyde as the coupling reagent. Four groups of Balb/c mice were immunized with the respective peptide-bovine serum albumin conjugates, and high titer antibodeis were obtained. The antibody raised by a particular species was not found to cross-react wtih the other species of malaria parasites' CSP repeat units
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