Malaria Parasite Fools Immune System By Switching Antigens

The plasmodium parasites that cause malaria attack red blood cells, cutting their way in and consuming the hemoglobin they find there. Normally the body quickly removes and recycles damaged cells, but these infected red blood cells are not allowed to continue circulating -- instead, the plasmodium parasites anchor infected cells to the inner wall of the blood vessel by secreting knoblike proteins that extend through the surface of the blood cell and stick to the blood vessel. The infected person's immune system detects the plasmodium knob proteins, and begins to mount a defense (as described in BIOLOGY 4/e: How Malaria Hides Fromn the Immune System, p. 1138). But during the several days before the human immune response becomes effective, some of the plasmodium parasites change their knob proteins. The plasmodium possesses many versions of the knob gene, and in these parasites a different version is being expressed. This sort of "antigen shifting" is a very powerful way to evade the human immune defense.

Source: "Malaria's Genetic Game of Cloak and Dagger" by Natalie Angier, New York Times, August 22, 1995.

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