BACKGROUND: The ability of Plasmodium falciparum to undergo antigenic variation, 
by switching expression among protein variants encoded by multigene families, 
such as var, rif and stevor, is key to the survival of this parasite in the 
human host. The RIFIN protein family can be divided into A and B types based on 
the presence or absence of a 25 amino acid motif in the semi-conserved domain. A 
particular type B RIFIN, PF13_0006, has previously been shown to be strongly 
transcribed in the asexual and sexual stages of P. falciparum in vitro.
METHODS: Antibodies to recombinant PF13_0006 RIFIN were used in 
immunofluorescence and confocal imaging of 3D7 parasites throughout the asexual 
reproduction and sexual development to examine the expression of PF13_0006. 
Furthermore, reactivity to recombinant PF13_0006 was measured in plasma samples 
collected from individuals from both East and West African endemic areas.
RESULTS: The PF13_0006 RIFIN variant appeared expressed by both released 
merozoites and gametes after emergence. 7.4% and 12.1% of individuals from East 
and West African endemic areas, respectively, carry plasma antibodies that 
recognize recombinant PF13_0006, where the antibody responses were more common 
among older children.
CONCLUSIONS: The stage specificity of PF13_0006 suggests that the diversity of 
RIFIN variants has evolved to provide multiple specialized functions in 
different stages of the parasite life cycle. These data also suggest that RIFIN 
variants antigenically similar to PF13_0006 occur in African parasite 
populations.