Primary infection of B6 mice with P. yoelii sporozoites is characterized by a peak of IFN-γ in the sera at day 5 post-infection. B6 mice were infected with 4,000 sporozoites of P. yoelii 265BY and the serum level of IFN-γ at days 0, 3, 4, 5, 6, 7, and 10 p.i. was determined by ELISA. Results from a pool of 6 independent experiments (3 to 21 mice per time point) are shown. Individual values (circles) and mean values (bars) are shown. NiSG: day-5 serum from B6 mice which received an injection of non-infected salivary gland extract. The statistical difference between day 0 (n = 17) and day 5 p.i. (n = 21) was calculated with the Mann-Whitney test.