Inability of Plasmodium vinckei-immune spleen cells to transfer protection to recipient mice exposed to vaccine 'vectors' or heterologous species of plasmodium.

Mice can be immunized to Plasmodium vinckei by repeated infections followed by cure. Such immunity is dependent on CD4 T cells and an architecturally modified spleen, but has little requirement for antibody. Thus, athymic mice can be exposed to P. vinckei and cured, but do not develop immunity. They are resistant to challenge with parasites, however, if they are then given spleen cells from euthymic immunized animals. Such immune spleen cells, however, cannot transfer resistance to normal mice which have been exposed to BCG, Salmonella typhimurium, or vaccinia virus, and are only partially effective in transferring resistance to mice which have been previously immunized with heterologous plasmodia, P. yoelii, P. chabaudi and P. berghei. Mice exposed to varying numbers of irradiated P. vinckei-pRBC do not develop immunity and nor are such animals protected following adoptive transfer of immune spleen cells. Cellular immunity to malaria may not only be dependent on a population of immune CD4 T cells, but may require a specifically architecturally modified spleen which may not occur following either exposure to candidate vaccine vectors, heterologous plasmodia or non-viable homologous plasmodia.