Relative biological effectiveness of negative pi mesons for the immune response in mice

Immunologically competent mouse spleen cells were exposed to negative pi mesons in the entrance plateau or at the peak of the dose distribution at a maximum dosage of 5 rads/min. or to 60Co gamma rays at 4.96 rads/min. Survival curves from cells irradiated in vitro but incubated in vivo yielded RBE values of 2.15 for the peak and 1.84 for the entrance plateau at a surviving fraction of 0.1. The dose-rate dependence of antibody-forming spleen cells for both 60Co gamma rays and the lot-LET components of the pion beam is discussed. The authors suggest that these RBE values constitute an upper limit for normal mammalian cells exposed to pions and tha the RBE with clinically useful dose rates may be significantly lower than those reported here.