Abstract
The inability of immature animals to respond to active immunization with the degree of demonstrable antibody production found in mature animals has been noted by numerous investigators. 1 Our experiments carried out in infantile, adolescent, and mature rabbits and rats indicated that increase in ability to form agglutinins to B. pertussis and B. typhosus was approximately coincidental with sexual maturation.
In an attempt to determine more accurately the effect of increasing age on agglutinin production and to correlate this, if possible, with some easily determined index of sexual development, the following experiment was performed. Ten groups of 5 male rats each were selected. The age of the groups increased by increments of 7 ± 1 days, the youngest group being 4 days old. All the rats were injected intraperitoneally with total doses of 9,000 million B. pertussis in 6 injections: 1,000 million per day for 3 days, 4 days' rest, and 2,000 million per day for 3 days. On the 17th day of the experiment, the animals were weighed and bled. Seminal vesicles and testes were weighed as an approximate measurement of the degree of sexual maturity. As the rats advanced in age, the results showed a general correlation between the rise in agglutinin titer on one hand, and the increase in testes, seminal vesicle, and body weights on the other. For example, the average body weight, seminal vesicle weight, testes weight, and agglutinin titer of 4-day-old rats were 34 gm., 8 mg., 182 mg., and 120, respectively; whereas those of 74-day-old rats were 211 gm., 511 mg., 2660 mg., and 2480.
Since sexual development and growth are both influenced by the endocrine balance, it appeared possible that changes produced by administration of gonadotropic and estrogenic hormones to immature animals might be reflected in the response of these animals to active immunization.
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