Date Published: November 11, 2016
Publisher: Public Library of Science
Author(s): Ariel Magallón-Tejada, Sónia Machevo, Pau Cisteró, Thomas Lavstsen, Pedro Aide, Mercedes Rubio, Alfons Jiménez, Louise Turner, Aida Valmaseda, Himanshu Gupta, Briegel De Las Salas, Inacio Mandomando, Christian W. Wang, Jens E. V. Petersen, Jose Muñoz, Joaquim Gascón, Eusebio Macete, Pedro L. Alonso, Chetan E. Chitnis, Quique Bassat, Alfredo Mayor, Michael J Blackman.
Cytoadhesion of Plasmodium falciparum infected erythrocytes to gC1qR has been associated with severe malaria, but the parasite ligand involved is currently unknown. To assess if binding to gC1qR is mediated through the P. falciparum erythrocyte membrane protein 1 (PfEMP1) family, we analyzed by static binding assays and qPCR the cytoadhesion and var gene transcriptional profile of 86 P. falciparum isolates from Mozambican children with severe and uncomplicated malaria, as well as of a P. falciparum 3D7 line selected for binding to gC1qR (Pf3D7gC1qR). Transcript levels of DC8 correlated positively with cytoadhesion to gC1qR (rho = 0.287, P = 0.007), were higher in isolates from children with severe anemia than with uncomplicated malaria, as well as in isolates from Europeans presenting a first episode of malaria (n = 21) than Mozambican adults (n = 25), and were associated with an increased IgG recognition of infected erythrocytes by flow cytometry. Pf3D7gC1qR overexpressed the DC8 type PFD0020c (5.3-fold transcript levels relative to Seryl-tRNA-synthetase gene) compared to the unselected line (0.001-fold). DBLβ12 from PFD0020c bound to gC1qR in ELISA-based binding assays and polyclonal antibodies against this domain were able to inhibit binding to gC1qR of Pf3D7gC1qR and four Mozambican P. falciparum isolates by 50%. Our results show that DC8-type PfEMP1s mediate binding to gC1qR through conserved surface epitopes in DBLβ12 domain which can be inhibited by strain-transcending functional antibodies. This study supports a key role for gC1qR in malaria-associated endovascular pathogenesis and suggests the feasibility of designing interventions against severe malaria targeting this specific interaction.
Case fatality rates for severe malaria (SM) remain unacceptably high even after administration of effective anti-malarial drugs . There is an urgent need to develop novel interventions against life-threatening malaria. However, the mechanisms underlying the clinical heterogeneity and spectrum of malaria  remain largely unknown. The general state of health and physiological condition of the host, in particular variations in host immunity, together with genetic predisposition and parasite factors involved in the virulence of the infection, might influence the progression of malaria towards a life-threatening outcome. Sequestration of infected erythrocytes (IE) in vital organs is believed to constitute a key pathogenic event in P. falciparum SM , eventually leading to hemorrhages, thrombi formation and pathological inflammation , all at the basis of microvascular obstruction [4–6]. Strategies to inhibit or prevent parasite sequestration thus have the potential to reduce the high fatality rate in SM.
The combined analysis of P. falciparum isolates from malaria infected Mozambique patients and an in vitro selected P. falciparum 3D7 line shows a relationship between cytoadhesion to gC1qR and transcription of DC8-type var genes. The clinical relevance of such a phenotype has been suggested in a field study conducted in Mozambique which showed that prevalence of parasite isolates exhibiting adhesion to gC1qR was associated with multiple seizures , although binding levels only tended to be higher compared with isolates from children with severe malaria. In the present study, the use of primer sets targeting the most clinically-relevant DCs [28,34,41] allowed us firstly to correlate the cytoadhesion to gC1qR with abundance of DC8 var transcripts in Mozambican isolates. Secondly, selection of P. falciparum 3D7 line for binding to gC1qR showed the up-regulation of the DC8-PFD0020c. Recombinant DBLβ12PFD0020c bound to gC1qR in ELISA assays and antibodies against this domain were able to inhibit binding of Pf3D7gC1qR and P. falciparum Mozambican isolates to gC1qR by 50%. Overall, these results point to the DBLβ12 domain present in DC8-PfEMP1 variants as the domain that mediates cytoadhesion to gC1qR.