Subtelomeric chromosome deletions in field isolates of Plasmodium falciparum and their relationship to loss of cytoadherence in vitro.

Subtelomeric deletions are responsible for the loss of expression of several Plasmodium falciparum antigens, including the knob-associated histidine-rich protein (KAHRP). Such deletions are detectable by two-dimensional pulsed-field gradient electrophoresis (PFGE) in which the chromosomes separated in dimension 1 are cleaved with Apa I, and the sizes of telomeric fragments are determined in dimension 2. This sensitive technique has enabled us to examine the role of subtelomeric deletions in two aspects of the biology of Plasmodium falciparum. First, we show that similar subtelomeric deletions to those that occur in vitro also occur in field isolates. Second, we demonstrate a correlation between subtelomeric deletions and loss of the phenotype of "cytoadherence" in cultured isolates. Subclones were generated from the cytoadherent cloned isolate ItG2F6, and their phenotypes were examined with respect to cytoadherence, the expression of "knobs," and agglutination of infected erythrocytes with rabbit antiserum. The only chromosomal change detectable by two-dimensional PFGE among subclones that differ from wild type in each of these three characteristics is a deletion of approximately 100 kilobases at one end of chromosome 2. This deletion includes the gene coding for KAHRP and the subtelomeric repeat designated rep20.