Both antibody dependent and cell mediated mechanisms contribute to immunity in malaria. The parasites vary in sensitivity to antibody mediated inhibition due to underlying antigenic variation. When Plasmodium falciparum isolates are tested with antibodies from the donor originally harbouring the parasites or with those from other donors, growth inhibition is usually lowest in the autologous combinations. Parasites with decreased sensitivity are also generated in vitro by culturing them for prolonged periods in the presence of certain anti-plasmodial antibodies. When the antibodies are removed, a successive return of sensitivity develops. The decrease in sensitivity to inhibition may either be due to down-regulation of synthesis of the antigen or a selection of parasites with low antigen expression from the heterogeneous original populations.