Monoclonal Antibodies against Murine Malarial Infection

Repeated inoculation of mice, monkeys, and humans with x-irradiated sporozoites can lead to sterile immunity against malarial infection (1, 2), Vaccinated animals have serum antibodies capable of neutralizing sporozoites (3) and of reacting with their surface membranes (4, 5). Exposure of humans to infected mosquitoes in endemic areas leads to the development of relatively high serum titers o f antisporozoite antibodies (6). Upon incubation with immune serum, viable sporozoites develop at their posterior end a thread-like precipitate which increases progressively in length (circumsporozoite precipitation [CSP] 1 reaction [7]). To clarify the nature of the antibody-parasite interaction and its relation to protective immunity, we recently used the technique of KiJhler and Milstein (8) to obtain hybrid cells between a plasmacytoma line and spleen cells from mice that produced antibodies to surface antigens of Plasmodium berghei. One clone of hybrid cells produced antibodies against a protein with an apparent 44,000 mol wt (Pb44), which envelops the surface membrane of sporozoites. In vitro incubation of the parasites with these antibodies abolished their infectivity (9). In this paper, we study the effects of this antibody and of its fragments on sporozoites in vitro and their protective effects in vivo against malarial infection.