Complement-mediated killing of Plasmodium falciparum erythrocytic schizont with antibodies to the recombinant serine repeat antigen (SERA).

Mouse antiserum against the recombinant N-terminal domain (SE47') of serine repeat antigen (SERA) of Plasmodium falciparum inhibited the in vitro proliferation of the parasite. We purified the immunoglobulin G from mice immunized with SE47' and with Freund's or aluminum hydroxide gel, or without adjuvants. Antiserum prepared with aluminum hydroxide gel contained predominantly IgG1 subclass and was the least inhibitory to parasite proliferation. Antiserum prepared with Freund's adjuvant or without adjuvants contained SE47'-specific IgG2a, IgG2b and IgG3. These mixed IgG subclasses was more potent in growth inhibition that the IgG1. Furthermore, guinea pig complement enhanced the parasite growth inhibitory effect of the mixed SE47'-specific IgG2a, IgG2b and IgG3, but not that of the IgG1 or non-specific IgG. Heat inactivated complement could not support the enhanced growth inhibitory effect. When purified schizonts were incubated with SE47'-specific IgG2a, IgG2b and IgG3 and complement, abnormal schizonts with degenerated nuclei were observed. These data suggest that complement-mediated lysis of the schizonts by the classical pathway enhances the inhibition of the parasite cell proliferation by SE47' specific IgGs.