Relative effectiveness of neutron and gamma radiation of trypanosomes for immunizing mice against African trypanosomiasis

Experiments carried out to compare the relative effectiveness of γ and neutron radiation for use in immunizing mice against Trypanosoma rhodesiense are reported. The results indicate that neutrons are relatively more effective than γ rays in reducing the infectivity of T. rhodesiense. With γ radiation, only 4 of 20 mice survived inoculations of trypanosomes irradiated at 10 kilorads in the 2 experiments; with neutron-irradiated trypanosomes 18 of 20 mice survived. A dose of 15 kilorads was sufficient to assure 100% survival of the mice when neutron radiation was used, but 20 kilorads was required with γ radiation. Neutron bombardment of T. rhodesiense was also more effective in immunizing against a challenge with the homologous parasite. It is shown that the mice immunized with trypanosomes exposed to high LET radiation had a greater survival rate when challenged. In addition, the mean survival time of the mice that died after challenge was longer in those immunized with neutron-irradiated parasites than in those innoculated with trypanosomes exposed to γ rays. (U.K.)