MSP-1 TCR Tg cells protect RAG^-/- mice from death and clear P chabaudi parasitemia only when B cells are present. (A) B5 and BALB/c CD4⁺ cells were purified (> 99%CD4⁺) by high-speed flow cytometry and transferred into RAG^-/- mice, which were then infected with 10⁴P chabaudi parasites. Parasitemia is shown as percent infected RBCs on a logarithmic (log₁₀) scale. (B) Mortality is shown as percent survival. RAG mice survive significantly better than RAG mice with B5 T cells P < .05 (log-rank test). (C) B5 and BALB/c CD4⁺ cells were purified by high-speed flow cytometry and transferred into nu/nu mice, which were then infected with 10⁴P chabaudi parasites. (D) A total of 5 × 10⁶ anti-OVA TCR Tg, DO11.10, CD4⁺ cells were purified and transferred into nu/nu mice; 50 μg OVA was given at the same time and the mice were infected with 10⁴P chabaudi. The courses of infection and mortality in BALB/c mice are shown for comparison. The infections shown are the mean parasitemias of 5 to 7 mice and are representative of 2 to 3 independent experiments. Error bars represent SEs of geometric means. (E-F) B5 Tg and BALB/c CD4⁺ cells were purified (> 99%) by high-speed flow cytometry and transferred into RAG2^-/- mice, which were then infected with 10⁴P chabaudi parasites. (F) Some mice were additionally immunized with the T-cell antigen (MSP1_900-1507) covalently linked to a protective B-cell antigen (MSP1_1658-1746 or MSP1₂₁) the day after T-cell transfer and 2 days before infection. Parasitemia is shown on a logarithmic (log₁₀) scale, and data are shown as geometric means of 5 to 8 mice and SEMs. Inset graphs in panels E and F represent the same parasitemia curves on a linear scale to day 14, with maximum of 45% iRBC on y-axis. ^* indicates significance of P < .05 by the Student t test.