A single i.v. injection of viable Ll2lO cells produced a classical immune response in rabbits, with -yM antibody activity first detected on Day 4, maximal on Day 6, and diminishing thereafter; in contrast, †̃yGactivity was detected

The immunization of rabbits with cells of mouse leukemia L1210 has been studied. The immune process was dissected into its †̃yMand †̃yGcomponents. The main objective was the preparation of antisera with high cytolytic potencies. A single i.v. injection of viable Ll2lO cells produced a classical immune response in rabbits, with -yM antibody activity first detected on Day 4, maximal on Day 6, and diminishing thereafter; in contrast, †̃yGactivity was detected on Day 8, was maximal around Day 14, and diminished there after. Interestingly, additional immunizations gave new peaks of †̃yMactivity, each smaller than the previous one. As ex pected, “K; activity rose sharply after secondary immunization and more gradually with further immunizations. For production of highly potent cytolytic antisera, repeated i.v. injection of large numbers of viable leukemia cells was the most effective procedure tested. Immunization with homog enized or sonically disrupted cells was significantly inferior. Evidence for immune exhaustion after long-continued immuni zation was obtained.