Complement receptor 1 is the host erythrocyte receptor for Plasmodium falciparum PfRh4 invasion ligand

The Walter and Eliza Hall Institute of Medical Research, Parkville 3052, Australia.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 10/2010; 107(40):17327-32. DOI: 10.1073/pnas.1008151107
Source: PubMed


Plasmodium falciparum is responsible for the most severe form of malaria disease in humans, causing more than 1 million deaths each year. As an obligate intracellular parasite, P. falciparum's ability to invade erythrocytes is essential for its survival within the human host. P. falciparum invades erythrocytes using multiple host receptor-parasite ligand interactions known as invasion pathways. Here we show that CR1 is the host erythrocyte receptor for PfRh4, a major P. falciparum ligand essential for sialic acid-independent invasion. PfRh4 and CR1 interact directly, with a K(d) of 2.9 μM. PfRh4 binding is strongly correlated with the CR1 level on the erythrocyte surface. Parasite invasion via sialic acid-independent pathways is reduced in low-CR1 erythrocytes due to limited availability of this receptor on the surface. Furthermore, soluble CR1 can competitively block binding of PfRh4 to the erythrocyte surface and specifically inhibit sialic acid-independent parasite invasion. These results demonstrate that CR1 is an erythrocyte receptor used by the parasite ligand PfRh4 for P. falciparum invasion.

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    • "During invasion, merozoite adhesins localize to the apical tip of the merozoite and interact with specific host receptors to initiate parasite entry [29]. A number of studies show that P. falciparum uses a key functional site in C receptor type-1 (CR1) for invasion of human Es [30], [31], [32]. CR1 is also the receptor for C3b, and as shown in Figure 3, the clustering of C3b deposition bears the hallmark of CR1 clustered distribution on the E [33]. "
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    ABSTRACT: Background Complement (C) is a crucial part of the innate immune system and becomes over activated during malaria, resulting in depletion of C components, especially those for lectin pathway (LP), thereby compromising the host's innate defense. In this study, involvement of P. falciparum antigens in C activation was investigated. Methods A highly synchronous culture of the Dd2 clone of P. falciparum was established in a serum free medium. Supernatants harvested from rings, trophozoites and schizonts at various parasite densities were tested for ability to activate C by quantifying amount of C3b deposited on erythrocytes (E). Uninfected sham culture was used as control. Remnants of each C pathway were determined using Wieslab complement System Screenkit (Euro-diagnostica, Sweden). To identify MBL binding antigens of LP, culture supernatants were added to MBL sepharose columns and trapped antigens eluted with increasing concentrations of EDTA (10 mM, 50 mM and 100 mM) and then desalted before being tested for ability to activate C. The EDTA eluate with highest activity was run on a polyacrylamide gel and silver stained proteins analyzed by mass spectroscopy. Results Antigens released by P. falciparum growing in culture activated C leading to C3b deposition on E. Maximal activation at 7% parasitemia was associated with schizont stage (36.7%) compared to 22% for rings, 21% for trophozoites and 3% for sham culture. All the three pathways of C were activated, with highest activation being for the alternative pathway (only 6% of C activation potential remained), 65% for classiical and 43% for the LP. Seven MBL binding merozoite proteins were identified by mass spectrometry in the 50 mM EDTA eluate. Conclusions MBL binding merozoite adhesins with ability to activate C pathway were identified. The survival advantage for such pronounced C activation is unclear, but opsonisation could facilitate recognition and invasion of E.
    PLoS ONE 08/2014; 9(8):e105093. DOI:10.1371/journal.pone.0105093 · 3.23 Impact Factor
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    • "Antigens identified as utilizing the SA-independent pathway are mainly, but not exclusively, comprised of the reticulocyte binding protein-like homologues (RH), RH2a, RH2b, RH4 and RH5 [9, 11–13]. The RBC receptors bound by RH2a and RH2b have not yet been fully identified; RH4 binds to complement receptor (CR) 1 [14], and RH5 binds to basigin [15]. "
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    ABSTRACT: Background The Plasmodium falciparum protein RH5 is an adhesin molecule essential for parasite invasion of erythrocytes. Recent studies show that anti-PfRH5 sera have potent invasion-inhibiting activities, supporting the idea that the PfRH5 antigen could form the basis of a vaccine. Therefore, epitopes recognized by neutralizing anti-PfRH5 antibodies could themselves be effective vaccine immunogens if presented in a sufficiently immunogenic fashion. However, the exact regions within PfRH5 that are targets of this invasion-inhibitory activity have yet to be identified. Methods A battery of anti-RH5 monoclonal antibodies (mAbs) were produced and screened for their potency by inhibition of invasion assays in vitro. Using an anti-RH5 mAb that completely inhibited invasion as the selecting mAb, affinity-selection using random sequence peptide libraries displayed on virus-like particles of bacteriophage MS2 (MS2 VLPs) was performed. VLPs were sequenced to identify the specific peptide epitopes they encoded and used to raise specific antisera that was in turn tested for inhibition of invasion. Results Three anti-RH5 monoclonals (0.1 mg/mL) were able to inhibit invasion in vitro by >95%. Affinity-selection with one of these mAbs yielded a VLP which yielded a peptide whose sequence is identical to a portion of PfRH5 itself. The VLP displaying the peptide binds strongly to the antibody, and in immunized animals elicits an anti-PfRH5 antibody response. The resulting antisera against the specific VLP inhibit parasite invasion of erythrocytes more than 90% in vitro. Conclusions Here, data is presented from an anti-PfRH5 mAb that completely inhibits erythrocyte invasion by parasites in vitro, one of the few anti-malarial monoclonal antibodies reported to date that completely inhibits invasion with such potency, adding to other studies that highlight the potential of PfRH5 as a vaccine antigen. The specific neutralization sensitive epitope within RH5 has been identified, and antibodies against this epitope also elicit high anti-invasion activity, suggesting this epitope could form the basis of an effective vaccine against malaria.
    Malaria Journal 08/2014; 13(1):326. DOI:10.1186/1475-2875-13-326 · 3.11 Impact Factor
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    • "Members of this family include: PfRh1, PfRh2a, PfRh2b, PfRh4, and PfRh5. So far only the host receptor for PfRh4 (Tham et al., 2010; complement receptor 1) and PfRh5 (Crosnier et al., 2011; basigin) have been identified. Except for PfRh5 (Baum et al., 2009), all the other members of this family are large type-1 transmembrane proteins. "
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    ABSTRACT: Emerging evidence suggests that antibodies against merozoite proteins involved in Plasmodium falciparum invasion into the red blood cell (RBC) play an important role in clinical immunity to malaria. The protein family of parasite antigens known as P. falciparum reticulocyte binding protein-like homolog (PfRh) is required for RBC invasion. PfRh5 is the only member within the PfRh family that cannot be genetically deleted, suggesting it plays an essential role in parasite survival. This antigen forms a complex with the cysteine-rich P. falciparum Rh5 interacting protein (PfRipr), on the merozoite surface during RBC invasion. The PfRh5 ectodomain sequence and a C-terminal fragment of PfRipr were cloned and expressed in Escherichia coli and baculovirus-infected cells, respectively. Immunization of rabbits with these recombinant proteins induced antibodies able to inhibit growth of various P. falciparum strains. Antibody responses to these proteins were investigated in a treatment-re-infection study conducted in an endemic area of Papua New Guinea (PNG) to determine their contribution to naturally acquired immunity. Antibody titers to PfRh5 but not PfRipr showed strong association with protection against P. falciparum clinical episodes. When associations with time-to-first infection were analyzed, high antibody levels against PfRh5 were also found to be associated with protection from high-density infections but not from re-infection. Together these results indicate that PfRh5 is an important target of protective immunity and constitutes a promising vaccine candidate.
    Frontiers in Microbiology 06/2014; 5:314. DOI:10.3389/fmicb.2014.00314 · 3.99 Impact Factor
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