Waves of Malarial var-iations

Waves of Malarial variations Minireview schizont-infected erythrocytes and surface reactive an-tibodies form clusters or agglutinates when they are Staffan Svä rd, and Per Hagblom mixed (SICA assay). In the human malaria parasite P. Microbiology and Tumor Biology Center falciparum, antigenic variation and switching has been Karolinska Institutet and attributed to P. falciparum erythrocyte membrane pro-Swedish Institute for Infectious tein 1, PfEMP1, encoded by the var genes (Baruch et PfEMP1, are produced by the intracellular parasite and Sweden are transported through the erythrocyte cytoplasm to the erythrocyte surface; that they are only soluble in ionic detergents suggests their stable insertion into the Parasites that proliferate in restricted ecological niches host cytoskeleton. PfEMP1 is an important adhesin me-such as Plasmodium spp. and those that repeatedly diating binding to both the vascular endothelium and to meet the immune system afresh like Giardia lamblia vary uninfected erythrocytes evident in the sequestration of their contact surfaces with the host by necessity in order infected erythrocytes in the microvasculature of the hu-to colonize, divide, and transmit themselves. This is in man host (reviewed by Miller et al., 1994). Why P. stark contrast to the " wait and see " strategy of microbes knowlesi has chosen to exhibit the SICA antigens to its such as Toxoplasma gondii which use host immune rec-primate host is not clear as the infected erythrocytes ognition as a means to stay dormant. do not sequester to a great extent. Regardless, it is Plasmodium malaria parasites dwell in the midst of anticipated that the SICA antigens have an important the immune system, in the bloodstream, where they function, and a speculative possibility is that they are infect erythrocytes to grow and divide. For all of their homologous to other surface-located polypeptides than asexual cycle, except a very short extracellular period, PfEMP1. Or is it so that PfEMP1 possesses still another they develop inside erythrocytes where they are pro-function besides that of an adhesin? tected from most effector mechanisms of the immune The SICA assay has revealed an extensive antigenic system. Yet, the parasite exports polypeptides to the variability of the P. knowlesi-infected erythrocyte sur-surface of the infected erythrocyte where it is open to face. Two SICA polypeptides are present on the infected intense attack from the humoral immune system. The erythrocyte surface yet the size difference between infected erythrocyte surface, its Achilles' heel, stimu-them is not large, not exceeding M r 20,000. It …