Plasmodium falciparum: comparison of in vitro growth of knobby and knobless isolates.

Variants (K-) of three strains of Plasmodium falciparum which do not produce the erythrocyte surface alterations that have been called knobs have been compared with their wildtype knobby (K+) parents. The K- variants achieve higher parasitemias, incorporate radiolabeled isoleucine more rapidly, and produce a higher percentage of multiply-infected cells than do their K+ parents. Nevertheless, immune owl monkey sera cause approximately the same percentage inhibition of growth of both K+ and K- organisms when included in the growth medium at a 1% concentration.