Antibody response to Plasmodium falciparum malaria. Comparisons of immunoglobulin concentrations, antibody titres and the antigenicity of different asexual forms of the parasite.

Antibody titres of children and adults living in a malaria endemic region were measured by the indirect fluorescent antibody technique, using fluorescein-conjugated monospecific immunoglobulin antisera. The antigenicity of trophozoites was compared with that of schizonts obtained by culture of infected blood. Malarial antibody was detected with antisera to IgG, IgM and, at low levels, to IgA but not with antisera to IgD or IgE. Higher titres were obtained with schizonts as the source of antigen than with trophozoites. Adults in whom IgM antibodies were detected had a mean IgM concentration significantly higher than that for individuals who were IgM antibody negative, and there was a positive correlation between IgG fluorescent antibody titres and total IgG in the children examined. Serial plasma samples from children with acute infections were examined to determine changes in immunoglobulin concentrations, antibody titres and the levels of serum antigens as a result of the infection.