Lipid antigens derived from erythrocytes infected with Plasmodium berghei

Lipids were extracted from red blood cells infected with Plasmodium berghei, from the membranes of infected red cells and from free parasites. A radioimmunoassay was used to detect antibodies to these lipids in sera from convalescent and immune rats. Most of the antigenic activity could be attributed to the parasite although some activity was found in lipids isolated from the membranes of infected red blood cells. Absorption studies showed that the binding was specific for malarial lipid antigens. Immune sera showed no cross-reactivity with lipids from red blood cells of non-infected rats. However, sera from non-infected control rats showed low levels of cross-reactivity with the parasitized red cell-derived lipids. Levels of anti-lipid antibodies were directly correlated with the progress of the infection. The highest antibody level occurred when the parasitaemia reached zero. The malarial lipids had no effect on lymphoblast transformation of immune splenocytes in vitro. However, liposomes prepared from either malarial or non-specific lipids caused an increased response to antigen by the blast cells.