T cell transfer for protection.

Ten female Ptprca (CD45.1) mice received a single dose of 100 μg anti-CD4 monoclonal antibody (clone YTS191.1) i.v. on day 3 prior to adoptive transfer. Spleens from 5 female C57BL/6 mice 3 days after the third immunization with 10⁶P. chabaudi AS centanamycin–attenuated prbcs or from naive C57BL/6 mice were processed (as described above for adoptive transfer) and CD4⁺ T cells isolated. 10⁷ CD4⁺ T cells were injected i.v. per CD4-depleted Ptprca mouse. Mice were challenged with 10⁵P. chabaudi AS prbcs i.v. on day 11 after transfer. Additionally, naive Ptprca mice and thrice immunized C57BL/6 that received either centamycin-attenuated nrbcs or P. chabaudi AS prbcs were all also challenged on the same day. Parasitemias and clinical scores were monitored. On day 7 after challenge, approximately 50 μl of blood was collected via tail from Ptprca mice that received no cells or CD4⁺ T cells from naive or immunized mice and evaluated for phenotype of host and recipient cells. Percent chimerism was calculated as the percentage of leukocytes that were CD3⁺CD4⁺CD45.2⁺CD45.1^–.