Antiparasite adherence activity in Thai individuals living in a P-falciparum endemic area

Two types of antimalaria antibodies in the serum of 54 villagers living in a malaria endemic area of Thailand were determined by indirect immunofluore scence assay in order to define the status of malaria immunity within the g roup, Antibodies to parasite-derived antigens in the membrane of ring stage -infected erythrocytes were very high (greater than or equal to 1:1,250) in 44%, moderate to low (less than or equal to 1:250) in 37% of the sera, and the rest did not have the antibody. However, all the sera had antibodies t o antigens of the intraerythrocytic mature parasites, showing a very high l evel in 65%, and moderate to low levers in 37% of the sera, Sera with high antibody titers to either type of antigen significantly inhibited cytoadher ence of P. falciparum-infected erythrocytes. All the sera variably inhibite d rosette formation of the parasites but showed no association with the ant ibody titers, These results suggest that the antibodies to cytoadherence an d rosette formation can be elicited and sustained in the malaria experience d host while living in the endemic area. This may be a natural preventive m echanism against the severity of P. falciparum infection in the infected ho st. How long the antiparasite adherence activity will last remains to be in vestigated.