In-vitro exoerythrocytic development of Plasmodium cynomolgi bastianellii: inhibitory activity of monoclonal antibodies against sporozoites of different P. cynomolgi strains and of P. knowlesi.

The inhibitory effect of anti-sporozoite monoclonal antibodies (MoAb) on the in-vitro development of liver stages of Plasmodium cynomolgi bastianellii (NIH strain) was evaluated using primary cultures of rhesus monkey hepatocytes. MoAbs against the circumsporozoite proteins of five strains of P. cynomolgi (NIH, London, Gombak, Ceylon, Berok), and of P. knowlesi (H strain) were used. Incubation of sporozoites of P. cynomolgi bastianellii with the anti-NIH strain MoAbs entirely prevented liver-stage development; MoAbs produced against the other four strains had no apparent activity. The anti-P. knowlesi MoAbs had a partially inhibitory effect on parasite development. These functional studies complement previous immunological studies on P. cynomolgi strain specificity, and confirm the cross-reactivity observed previously between sporozoites of P. cynomolgi bastianellii and P. knowlesi (H strain).