Figure 3. DARC polymorphisms affect the functional properties of DBPII antibodies.

DBPII binding inhibitory antibodies (BIAbs) were evaluated in plasma from individuals stratified according to DARC alleles, as carrying double positive alleles (FY*A/FY*A, FY*A/FY*B, FY*B/FY*B) or a single positive allele (FY*A/FY*B^ES, FY*B/FY*B^ES). A) Frequencies of BIAbs (top of the columns) at three consecutive surveys showed DBPII BIAbs to be significantly more frequent in single positive allele carriers than in double positive carriers (significant differences between a vs. a′; b vs. b′ and c vs. c′, as determined by by Z-test, P<0.05.); B) After 12-months, the BIAbs response was more persistent in the group carrying a single DARC-positive allele (Z-test = 3.002; P = 0.0027). NR  =  non-responder, no inhibitory antibody response detected at any time-point of the study; TR  =  temporary responder, inhibitory antibodies in at least one cross-sectional survey; (PR  =  persistent responder; inhibitory antibodies detected in all surveys. BIAbs were evaluated by COS-7 cyto-adherence assay, with plasma samples at 1∶40 and positive results as DBPII –DARC binding inhibition ≥ 50%.