Trypanosoma lewisi: Immune spleen cell transfer in rats

Inbred Lewis rats infected with Trypanosoma lewisi tended to fall into two groups of high and low parasitemias. The levels of parasitemia were expressed as accumulative values for the first seven days (S₀⁷) of infection. Splenectomy, performed two days preinfection, yielded values of S₀⁷ beyond the range of the highest normals. An attempt was then made to demonstrate that immune splenic cells confer immunity in normal rats. Splenocytes were obtained from normal and immune rat spleens, and administered by tail vein into rats five days before challenge. Transplants of normal splenocytes did not seem to alter the pattern of the normal infection. The same number of cells from spleens of early convalescent animals (12 days of infection) reduced the levels of infection to the lowest S₀⁷ values. Splenic cells taken just as the infection came under control on the seventh day (and accompanied by a few trypanosomes) were incapable of controlling the infection. In a few animals adoptively immunized, low levels of agglutinative antibody were detectable five days after cell transfer. In contrast to splenic cells taken on the Day 7, plasma from these animals did neutralize a challenging dose of simultaneously injected trypanosomes. These two points, considered with the effect of splenectomy in producing lowered γ globulin levels, suggested that "humoral" factors outweigh "cellular" ones in immunity to T. lewisi.