Maturation of the intracellular parasite and antigenicity.

The protein antigens synthesized by the malarial parasite change as the parasite matures, with a number of proteins showing strict stage-specificity. A detailed correlation between the stage-specificity of protein synthesis and parasite structure has yet to be established, but a number of proteins synthesized in the cycle are lost selectively during merozoite escape and reinvasion. These antigens are presumably associated with structures utilized and ultimately lost during this process. Particular interest has focused on some greater than 200K proteins identified as being on the surface of infected erythrocytes and internally and on the surface of merozoites. Smaller parasite proteins have also been identified in the erythrocyte membrane. The erythrocyte itself, including its membrane, is much modified by parasite growth. Changes include the presence of new cytoplasmic structures and differences in the surface labelling and isoantigenic characteristics of the surface membrane. An appreciation of the variability and specificity of exposed parasite antigens, and their relationship to newly exposed isoantigens, is central to our understanding of protective immunity to malaria.