MSP1-specific TCR Tg T cells help B cells produce quicker and greater levels of malaria-specific antibody. (A-F) 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. Antibodies specific for (A) MSP1_1-672, (B) MSP1_581-921, (C) MSP1_900-1507, (D) MSP1_1508-1766, (E) whole parasite lysate, and (F) recombinant AMA-1 were measured in the plasma of samples taken weekly during the course of a P chabaudi infection. Specific IgG antibody is expressed as arbitrary units relative to a standard hyperimmune serum (1000 AU). The values shown are the geometric means and SEs of units of antibody measured in plasma of 5 to 7 mice. The asterisk indicates significant differences (P < .05, Student t test). (G) B5 TCR Tg T cells are still specific to MSP1_900-1507 after 40 days of exposure to a P chabaudi infection in vivo. Lymph node cells were taken 6 weeks after infection from nu/nu mice reconstituted with B5 and BALB/c T cells and stimulated with 4 MSP-1 recombinant fragments in vitro (from left to right, MSP1_1-672, MSP1_581-921, MSP1_900-1507, and MSP1_1508-1766). Proliferation was determined by ³H-thymidine incorporation for the last 12 hours of culture.