Antibodies to the PF155 antigen of Plasmodium falciparum: measurement by cell-ELISA and correlation with expected immune protection.

Plasmodium falciparum polypeptide Pf155 is one of the main candidates for a vaccine against asexual blood stages of P. falciparum. Antibodies against Pf155 can be detected by a cell-ELISA technique with glutaraldehyde-fixed and air dried P. falciparum-infected erythrocytes as antigen. Using this assay, we measured the level of antibodies in sera from 230 subjects with various degrees of past exposure to P. falciparum. Significant levels of antibodies (OD492 greater than 0.5) were detected in 41/50 sera from Central African adults and in 34/50 sera from West African adults. All sera from 50 European adults suffering primary malarial attack and 28/30 sera from West African children (10 to 12 years old) were negative. Intermediate results were obtained with 50 sera from West African adults living in France for greater than or equal to 2 years (12 positive). Mean OD values of the sera of these five groups of subjects varied in the same direction as the positivity rates. These preliminary results suggest that the level of anti-Pf155 antibodies as detected by cell-ELISA might provide an assessment of protective immunity against P. falciparum which could complement clinical or epidemiological criteria.