Use of stable sensitized cells in an improved indirect microhemagglutination test for malaria

VIVAX AND 86% FOR P. FALCIPARUM. FURTHER EVALUATION HAS SHOWN THAT THE SENSITIVITY OF THE P. KNOWLESI ANTIGEN FOR ELUATES OF FILTER PAPER FROM INDIVIDUALS INFECTED WITH HUMAN MALARIA SPECIES WAS 82%. THE TITER RESPONSE OF AN ANTIGEN WITH A SERUM IS A MEASURE OF ITS REACTIVITY. THE REACTIVITY OF P. KNOWLESI ANTIGEN WITH P. VIVAX SERA IS ALMOST THE SAME AS THAT OF P. VIVAX ANTIGEN. WITH SOME P. FALCIPARUM SERA, HOWEVER, P. KNOWLESI ANTIGEN PRODUCES LOWER TITERS THAN THOSE OBTAINED WITH P. FALCIPARUM ANTIGEN. IN GEOGRAPHIC AREAS WHERE P. FALCIPARUM IS THE PREDOMINANT MALARIA SPECIES, WE NOTED A DECREASE IN SENSITIVITY OF THE INDIRECT MICROHEMAGGLUTINATION (IMHA) TEST, PARTICULARLY WITH SERA FROM CHILDREN. IN THE BELIEF THAT THIS MAY BE DUE TO THE DECREASED REACTIVITY OF THE P. KNOWLESI ANTIGEN WITH P. FALCIPARUM SERA, AN ATTEMPT WAS MADE TO EVALUATE A MIXTURE OF P. KNOWLESI AND P. FALCIPARUM ANTIGEN TO SEE IF THE TITERS OBTAINED WITH THE MIXTURE OF CELLS WERE HIGHER. WHEN THE CELLS SENSITIZED WITH THE TWO ANTIGENS WERE MIXED IN A 1: 1 RATIO, MOST OF THE TITERS OF P. VIVAX SERA WERE LOWER OR EQUAL TO THE TITERS OBTAINED WITH THE P. KNOWLESI ANTIGEN, BUT WERE MARKEDLY HIGHER THAN THOSE OBTAINED WITH THE P. FALCIPARUM ANTIGEN. THE SAME TREND WAS TRUE FOR THE P. FALCIPARUM SERA. THE TITERS WERE MARKEDLY HIGHER THAN THOSE OBTAINED WITH THE P. KNOWLESI ANTIGEN AND SLIGHTLY LOWER THAN THOSE OBTAINED WITH THE HOMOLOGOUS ANTIGEN.