It was reported previously [8] that germfree (GF) mice infected with virulent bovine type tubercle bacilli showed more extensive and progressive infections than conventional mice; marked differences between GF and conventional mice were observed only in later stages of the infections. The lesions in GF mice were characterized by infiltration with many histiocytic cells engorging acid fast bacilli. These facts seemed to implicate an impaired immunological response following the infection in GF mice. It has been reported by Lerner [2] and Lev and Battisto [3] that GF guinea pigs showed a suppressed delayed type hypersensitivity. In the present experiments, we found an impaired delayed type footpad reaction to purified protein derivative (PPD) in GF mice infected or sensitized with the tubercle bacilli, and attempts were also made to restore the reactivity by association with enteric bacteria.

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A comparative study of the tuberculin potency and reactivity to TAP and PPD-S was made in humans and guinea pigs. A comparison of reactions elicited by TAP and PPD-S was made in two groups of guinea pigs previously inoculated with killed bacilli or with living bacilli. The tuberculin reactions produced by TAP and PPD-S in human beings was studied in school children from rural districts. These children were divided randomly into three groups and each group was given a different amount of TAP and PPD-S. The results obtained are as follows: (1) While relative potency of TAP was relatively much weaker than PPD-S in guinea pigs sensitized with tubercle bacilli, in human beings the tuberculin potency of TAP was approximately 1/2 or 1/3 that of PPD-S. (2) There was a marked difference in the tuberculin reactivity to TAP and PPD-S between guinea pigs immunized with killed bacilli and guinea pigs immunized with living bacilli.

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SUMMARY: Immune response of man to tetanus and diphtheria-tetanus com bined toxoids with different compositions was investigated, with special reference to the long-term immunity. Adsorbed tetanus toxoid with a potency of about 25 IU per human dose endowed a long-lasting immunity sufficient to prevent tetanus to the vaccinees of various age groups, when administered in two doses, followed by a booster injection.Two doses of adsorbed diphtheria-tetanus combined toxoid with potencies of about 20 IU per dose for both components were sufficient to give immunity in infants against diphtheria and tetanus. However, a booster injection should be given within a year to endow a long-lasting immunity.In the case of booster immunization of children with a complete history of im munization against diphtheria and tetanus, a potent long-term immunity was endowed by a single injection of diphtheria-tetanus combined toxoid (plain) with 1 and 3.5 IU per dose, for diphtheria and tetanus components, respectively.