Invasion and growth of Plasmodium falciparum in different types of human erythrocyte.

The susceptibility of human red blood cells to invasion by Plasmodium falciparum was investigated in microtissue cultures with different populations of erythrocytes containing fetal haemoglobin (HbF). Preferential invasion of HbF-containing erythrocytes was observed with umbilical cord blood. The parasites showed no preference for HbF cells in blood from a subject with hereditary persistence of fetal haemoglobin (HPFH). By contrast, a significant preference for HbA-containing erythrocytes was found with blood from young infants. Further experiments demonstrated that falciparum parasites preferentially invade "young" erythrocytes. This could explain the distribution of parasites found in blood containing HbF, because HbF-containing erythrocytes are "younger" on average in cord blood, "older" in the blood of infants, and of the same average age as HbA-containing cells in HPFH. We concluded that the susceptibility of human erythrocytes to invasion by P. falciparum is not correlated with the presence of HbF, but that aging of red cells in vivo decreases their susceptibility to invasion. Semi-quantitative measurements were made of parasite growth in cells containing HbA or HbF. The growth of individual parasites in cells containing HbF was significantly retarded. This might confer a selective advantage on individuals with thalassaemia and sickle cell trait, in which HbF levels are raised in early life.