IFNG and malaria: This positivity definition was adapted for a study measuring naturally acquired ELISpot IFN-γ responses to the P. falciparum cell-traversal protein for ookinetes and sporozoites (CelTOS) in Ghana, namely a stimulation index of >2.0 (response obtained with PBMCs stimulated with malaria antigen peptides compared to medium alone) and a difference of 10 sfc/m between antigen-stimulated and unstimulated PBMCs [27].