The mature erythrocyte surface antigen of Plasmodium falciparum is not required for knobs or cytoadherence.

Intraerythrocytic Plasmodium falciparum parasites at the trophozoite and schizont stages synthesize a greater than 200-kDa protein, the mature erythrocyte surface antigen (MESA), that is localized at the membrane of infected red blood cells and manifests size polymorphism and antigenic diversity among parasite isolates. Because MESA is localized in the host cell membrane, we examined parasites with differing knob and cytoadherence phenotypes to determine whether MESA expression correlated with knob formation and cytoadherence. A cloned line of P. falciparum that was cultured with repeated selection for the knobbed and cytoadherent phenotypes did not express MESA, due to at least partial deletion of the single-copy MESA gene. In contrast, parasites from the same clone that were cultured without this selection lost the knobbed and cytoadherent phenotypes, but continued to express MESA. These results indicate that MESA is apparently not required for differentiation and multiplication of erythrocyte stage P. falciparum parasites in vitro, or for knob formation and cytoadherence. We speculate that MESA may have a role in evasion of the host immune response by P. falciparum.