Following stimulation with a high dose of polio-virus both 19S and 7S antibodies were formed. The kinetics of their formation differed in several respects: (a) 19S antibody preceded 7S antibody by 1 days; (b) 19S antibody rose to peak titers at a rapid exponential rate within 1 week, while 7S antibody increased at a slow decelerating rate for 3 weeks; (c) 19S antibody formation was short-lasting while 7S antibody synthesis endured. A renewed formation of both antibodies occurred following restimulation with a high antigen dose. The secondary 19S and 7S antibody responses were similar to the respective primary responses, and the preexistence of 7S antibody synthesis did not detectably alter the secondary 19S response.

Both 19S and 7S antibodies were formed and the kinetics of their formation was similar (a) for infectious and non-infectious (UV-) poliovirus antigen; (b) for the serologically unrelated poliovirus and Coxsackie B-4 virus; (c) when poliovirus was administered by different routes; (d) when 1-day-old or adult rabbits were immunized; (e) in antibody responses to poliovirus in rabbit, guinea pig, and man.

Whole body x-irradiation 20 hours prior to antigenic stimulus (high dose) resulted in delayed but markedly prolonged 19S antibody formation and inhibition of 7S antibody synthesis.

Thus, the formation of 19S and 7S antibody differed in (a) antigen dose requirements for induction and maintained synthesis; (b) kinetics; (c) retention of memory; and (d) sensitivity to prior x-irradiation. These differences are best explained on the assumption that the two antibodies are produced by different cells.