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The IgG subclass levels of anti-Plasmodium falciparum antibodies in human sera were determined in ELISA with monoclonal mouse antibodies specific for the human IgG subclasses as analytical reagents. The parasite antigen was a trophozoite/schizont enriched preparation of in vitro cultivated P. falciparum. Serum samples were from Swedish malaria patients and adult Liberians. Parasite specific antibodies were found in all four subclasses. Relatively elevated levels of IgGl antibodies were found both in Swedish patients and in the Liberians. Relative to the Liberians, high IgG2 antibody levels were seen in most Swedish patients. In Liberian sera but not in those from Swedish patients elevated IgG3 levels were found. In two Swedish patients followed consecutively for a period of 15 weeks, elevated levels of IgG1 and IgG3 antibodies were seen after relapse. No differences between the groups in regard to the levels origG4 antibodies were noticed. The differences between the Swedish patients and the Liberians were also in part reflected by differences in the total amounts of the four IgG subclasses. [ABSTRACT FROM AUTHOR]

Isotypes (IgM and IgG-1 to 4) of anti-P. falciparum antibodies were investigated in sera of malarial patients or immune donors by enzyme linked immunosorbent assay (ELISA) and two indirect immunofluorescence assays (IFAs), one staining intra-erythrocytic parasites of all stages and the other a restricted number of parasite antigens deposited in the membrane of infected erythrocytes by invading merozoitcs (Perlmann & Wahlgren, 1983; Perlmann et al., 1984, Wahlgren et al., 1985 a). There was no correlation in overall antibody titre between the two IKAs. Antibodies of both IgM and all tour IgG isotypes were detected in both assays. With the IFA for intracellular parasites a brilliant fluorescence was obtained with antibodies of all isotypes. However IgG-2 antibodies often gave staining restricted to the surface of schizonts. The incidence and reactivity in individual sera of antibodies of the different isotypes did not relate to the immune status of the donors (acute infection or clinically immune) but related well to the degree of malarial exposure as reflected by the overall antibody titres. This, in all three assays, high titred sera frequently contained antibodies of all isotypes white low titred sera usually only contained antibodies of IgM, IgG-1 and IgG-3 isotype. On average, the overall expression of antibodies of different isotypes in individual sera appears to reflect a sequential downstream (5' to 3') activation of the corresponding Igh-C genes in P. falciparum specific B cell clones. [ABSTRACT FROM AUTHOR]