Expression of the histidine-rich protein PfHRP1 by knob-positive Plasmodium falciparum is not sufficient for cytoadherence of infected erythrocytes.

Six culture-adapted knob-positive Plasmodium falciparum parasites, four of which were nonbinding in an in vitro cytoadherence assay, were tested for the presence of the knob-associated histidine-rich protein PfHRP1. Two knob-positive, strongly cytoadherence-positive P. falciparum strains from Aotus monkeys were also examined. All parasites expressed PfHRP1, suggesting that it plays a structural or functional role related to knobs but is not by itself sufficient for cytoadherence of P. falciparum-infected erythrocytes.