Analysis of antibody cross-reactivity within amino sequence cluster groups of AMA1 alleles. A) Classification of the 11 AMA1 alleles into the sequence cluster groups described by Duan et al.  (based on the sequence including domains I, II and III (excluding the prodomain)). B) Antibody cross-reactivity measured by competition ELISA for AMA1 alleles within each cluster group. Alleles within each group were compared pairwise with each other. C) Level of antibody cross-reactivity between AMA1 alleles within the same cluster group, compared to cross-reactivity between AMA1 alleles in different clusters - a total of 88 pair-wise comparisons of cross-reactivity was made. The median cross-reactivity of alleles (bar) within the same sequence cluster group was only slightly higher compared to cross-reactivity of alleles from different clusters (p = 0.012; median cross-reactivity was 48.5% for same cluster and 37% for different cluster). Data on antibody cross-reactivity were obtained from testing PNG children. AMA1, apical membrane antigen 1; PNG, Papua New Guinea.