Figure 4. Cellular responses and cross-reactivity.

(A) To determine CD4 response, A/J mice were immunized with 10³ (AS) prbc in CpG-ODN (black bars) or control ODN (gray bars). Spleen cells collected 2 weeks after immunization were cultured with homologous (AS) or heterologous (P. c. chabaudi AJ [AJ]; P. yoelii YM [YM]) parasites, normal rbc (nrbc), or ConA. After 96 hours, supernatants were assayed for TNF-α, IFN-γ, IL-2 (Th1 cytokines), and IL-4 or IL-5 (Th2 cytokines) assessed. Results are mean ± SEM. (B) For proliferation, spleen cells from A/J mice immunized as above were purified at 2, 8, or 12 weeks and incubated for 96 hours with AS, AJ or YM prbc, nrbc, medium, or ConA. Numbers represent percentage of CFSE^dim CD4 T cells. (C) For cytokine secretion, spleen cells from A/J mice immunized as above and purified at 2, 8, or 12 weeks were incubated for 96 hours with AS, AJ, or YM prbc, nrbc, or medium and stained for intracellular IFN-γ. Numbers represent percentage of IFN-γ⁺ CD4 T cells. (D) For cross-reactive antibodies, sera from A/J mice immunized with 10³ (AS) prbc in CpG-ODN (black bars), control ODN (gray bars), or hyperimmune sera (HIS, white bars) were tested for IgG titers against homologous (AS) or heterologous (AJ and YM) parasites. Results represent reciprocal median total IgG titers and interquartile ranges. All data sets are representative of 5 mice per group of 3 independent experiments performed. Significant differences compared with controls are shown. *P < 0.05.