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 immunofluorescence assay in order to define the status of malaria immunity within the group. Antibodies to parasite-derived antigens in the membrane of ring stage-infected erythrocytes were very high (> or = 1:1,250) in 44%, moderate to low (< or = 1:250) in 37% of the sera, and the rest did not have the antibody. However, all the sera had antibodies to antigens of the intraerythrocytic mature parasites, showing a very high level in 65% and moderate to low levels in 37% of the sera. Sera with high antibody titers to either type of antigen significantly inhibited cytoadherence of P. falciparum-infected erythrocytes. All the sera variably inhibited rosette formation of the parasites but showed no association with the antibody titers. These results suggest that the antibodies to cytoadherence and rosette formation can be elicited and sustained in the malaria experienced host while living in the endemic area. This may be a natural preventive mechanism against the severity of P. falciparum infection in the infected host. How long the antiparasite adherence activity will last remains to be investigated.