Level of Serum Antibody Associated with Intracerebral Immunity in Monkeys Vaccinated with Lansing Poliomyelitis Virus

Abstract

Rhesus monkeys have been vaccinated intramuscularly with graded amounts of active Lansing poliomyelitis virus. The proportion of individuals immune to the subsequent intracerebral injection of 10,000 PD50 of active virus was found to rise with increasing dosage of vaccine. In a total of 79 vaccinated monkeys, serum taken before intracerebral challenge was titrated by mouse neutralization test. As serum titer rose, a greater proportion of individuals proved to be immune. The minimal level of serum antibody associated with complete immunity of the group was found to be 3.0 (1/1000 dilution of serum). These quantitative data give further information on the required level of serum antibody associated with immunity in an experimental animal, established by a severe test. They also provide us with an effective means of vaccination of monkeys which has served as a basis for type differentiation of strains of poliomyelitis virus.