Interferon- γ responses to Plasmodium falciparum vaccine candidate antigens decrease in the absence of malaria transmission

Background. Malaria elimination campaigns are planned or active in many countries. The effects of malaria elimination on immune responses such as antigen-specific IFN- γ responses are not well characterized. Methods. IFN- γ responses to the P. falciparum antigens circumsporozoite protein, liver stage antigen-1, thrombospondin-related adhesive protein, apical membrane antigen-1, MB2, and merozoite surface protein-1 were tested by ELISA in 243 individuals in highland Kenya in April 2008, October 2008, and April 2009, after a one-year period of interrupted malaria transmission from April 2007 to March 2008. Results. While one individual (0.4%) tested positive for P. falciparum byPCRinOctober 2008 and another two (0.9%) tested positive in April 2009, no clinical malaria cases were detected during weekly visits. Levels of IFN- γto all antigens decreased significantly from April 2008 to April 2009 (all P < 0.001). Discussion. Naturally acquired IFN- γ responses to P. falciparum antigensare shortlived in the absence of repeated P. falciparum infection. Even short periods of malaria interruption may significantly decrease IFN- γ responses to P. falciparum antigens.