Figure 1. Definition of a low-dose whole-parasite vaccine.

(A) To define the low-dose vaccine, A/J mice were immunized with decreasing doses of P. c. chabaudi AS (AS) antigen equivalent to 10⁸, 10³, 10², or 0 (adjuvant alone) prbc in CpG-ODN or control ODN. 2 weeks after immunization, mice were challenged i.v. with 10⁵ homologous (AS) prbc and the outcome of infection monitored as parasitemia. Disease severity is also described in Supplemental Figure 1. Data for individual mice are shown. ^†Animals that succumbed to infection. (B) To assess cellular immune responses induced by vaccination, antigen-specific proliferation of splenic lymphocytes was assessed at the time of challenge infection. Spleen cells were cultured for 96 hours in the presence of fresh (AS) parasitized rbc (P), normal rbc (N), medium (M), or ConA (C) and proliferation assessed by thymidine uptake. Results show mean ± SEM. (C) To assess vaccine-induced antibody responses, parasite-specific IgG titers against homologous (AS) antigen were assessed by ELISA at the time of challenge. Reciprocal median total IgG titers and interquartile ranges are shown. All results are representative of 5 mice per group of 3 independent experiments performed. Significant differences compared with adjuvant alone (control ODN or CpG-ODN) are shown. *P < 0.05; **P < 0.01. HIS, hyperimmune sera.