Antígenos variantes de superfície de hemácias infectadas por Plasmodium falciparum na Amazônia brasileira: aderência a receptores do endotélio vascular (CD36 e ICAM-1) e reconhecimento por anticorpos.

Abstract

Malaria is one of the major parasitic endemic diseases in Brazil with 460,000 clinically notified cases in 2007. The relative rarity of severe malaria in Brazil suggests that the local Plasmodium falciparum isolates are less virulent than African and Asian parasites. P. falciparum virulence is mainly due to its ability to adhere to the vascular endothelium receptors through variant surface antigens (VSA) exported to the infected red blood cell membrane. This work investigated adherence patterns to CD36 and ICAM-1, two receptors of the vascular endothelium, in P. falciparum isolates from an area of the Brazilian Amazon, where severe malaria is rare. We also analyzed, in the same area, the antibody responses of people against eight VSAs. We found that: (a) local P. falciparum isolates express VSAs capable to adhere to both receptors, CD36 and ICAM-1, although in a few cases adherence is weak or absent; (b) we detected antibodies against VSAs in a human population exposed to malaria, expressed from local parasites and the 3D7 control; (c) we found in vitro that some sera contained naturally acquired antibodies which blocked the adherence of the parasitized RBCs to ICAM-1 and CD36; (d) we detected a low frequency of the S allele (hemoglobin S) in the study population. This supports the hypothesis that HbS do not represent a significant selection factor for high adherence capacity to endothelial receptors in these local isolates.