Ex vivo desequestration of Plasmodium falciparum-infected erythrocytes from human placenta by chondroitin sulfate A

We performed ex vivo experiments with Plasmodium falciparum-infected human placentas from primi- and multigravida women from Cameroon. All women, inde pendent of their gravida status, had anti-chondroitin sulfate A (CSA) adhes ion antibodies which cross-reacted with heterologous strains, such as FCR3 and Palo-Alto(FUP)1, which were selected for CSA binding. These antibodies, directed against the surface of infected erythrocytes obtained by flushing with CSA (IRBCCSA), were restricted to the immunoglobulin G3 isotypes. Mas sive desequestration of parasites was achieved with soluble CSA but not wit h anti-ICAM-1 and anti-CD36 monoclonal antibodies. All of the CSA-flushed p arasites were analyzed immediately by using in vitro assays of binding to S aimiri brain endothelial cells (SBEC) expressing various adhesion receptors , Parasites derived from all six placentas displayed the CSA adhesion pheno type. However, only partial inhibition of adhesion was observed in the pres ence of soluble CSA or when Sc1D SBEC were treated with chondroitinase ABC, These results suggest that an additional adhesive molecule of IRBCCSA whic h binds to an unidentified receptor is present in the placenta. This new ph enotype was lost once the parasites adapted to in vitro culture. We observe d additional differences in the CSA adhesion phenotype between placental pa rasites and in vitro-cultured parasites panned an endothelial cells carryin g CSA. The minimum size of fractionated CSA required for a significant inhi bition of placental IRBCCSA adhesion to Sc1D cells was 1 to 2 kDa, which co ntrasts with the 4-kDa size necessary to reach equivalent levels of inhibit ion with panned IRBCCSA of this phenotype. All placental IRBCCSA cytoadhere d to Sc17 SBEC, which express only the CSA receptor, Fanning of IRBCCSA on these cells resulted : In a significant quantitative increase of IRBC cytoa dhering to the CSA of Sc1D cells but did not change their capacity for adhe sion to CSA on normal placenta cryosections. Our results indicate that the CSA binding phenotype is heterogeneous and that several distinct genes may encode P. falciparum-CSA ligands with distinct binding properties.