The direct antiglobulin test in P. falciparum malaria

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Abstract
The direct antiglobulin test (DAT) was performed on 134 Gambian children with P. falciparum malaria. A positive DAT resulted for 52 children and in 25 this was due to the adherence of [complement] C3 to their red cells while 13 showed sensitization with IgG as well as C3. Sensitization with C4 alone or in association with IgG and/or C3 was rarely found. The Hb levels and reticulocyte counts were not significantly different in patients with a positive DAT from those with a negative DAT. Children with positive IgG DAT were of a significantly older age group and had significantly higher parasitemias than children with complement components only or with a negative DAT. In vitro assay of phagocytosis showed that PBM (peripheral blood monocytes) from malarious patients were less active in phagocytosis than normal male adult Caucasian PBM. Neither PBM from malarious patients nor normal adult Caucasians PBM showed phagocytosis of cells from DAT positive malarious children. A schizont-specific opsonizing antibody was present in the sera of adult Gambians and in children with a positive DAT due to IgG but not in sera of patients with a negative IgG. Evidently, a positive IgG DAT in malaria does not necessarily lead to excess hemolysis of non-parasitized red cells. The presence of a schizont opsonizing antibody indicates a relationship between the development of the positive DAT and acquisition of protective malarial immunity.