The active immunization of guinea-pigs passively immunized with homologous antitoxic serum

Groups of guinea-pigs were passively immunized against diphtheria toxin with homologous antitoxic serum so that their sera contained, at the start of the experiment, 1·0, 0·1, 0·01 or 0·001 unit/ml, respectively. They were then actively immunized with one, or two spaced, injections of 0·1 Lf of A.D.F. Two control groups were included, one passively immunized only and the other actively immunized only.

Passively produced serum titres of 0·01 and 0·001 unit/ml. did not interfere with active immunization in any demonstrable way.

A titre of 0·1 unit/ml. did interfere with active immunization, markedly 4 weeks after the primary, slightly 2 weeks after the secondary, and markedly 14 weeks after the secondary, stimulus.

A titre of 1·0 unit/ml. interfered with active immunization, markedly 4 weeks after the primary, and 2 and 14 weeks after the secondary, stimulus. This titre, however, did not completely annul the effect of the primary stimulus. The highest observed serum titre was obtained at the 32nd, instead of at the 4th week, as in the guinea-pigs actively immunized only.

In large measure the results confirm those of Barr and her colleagues who found that, in human babies, an initial ‘passive’ titre of 0·04 unit/ml. serum did not interfere with active immunization, whereas a titre of 0·1 unit/ml, led to unsatisfactory immunization.

A comparison of human antisera to purified diphtheria toxoid with antisera to other purified antigens by quantitative precipitin and gel diffusion techniques

The limits of sensitivity of three gel diffusion methods are compared and their utilization in the detection of small amounts of antibody to antigens present in traces in a preparation is illustrated with the diphtheria toxin-human antitoxin system. The Preer modification of the Oakley-Fulthorpe technique and the Oudin tube method were found more sensitive than the Ouchteriony plate method, and permitted the detection of as little as 3 microg. antibody N/ml. of serum. Antisera from eight Schick-negative individuals immunized with purified diphtheria toxoid have all been shown to contain, in addition to antitoxin, antibodies to substances present as impurities in the purified toxoid injected. The amounts of these antibodies in a serum and a partial characterization of their antigen-antibody curves have been determined through the combined use of quantitative precipitin and gel diffusion methods. Different amounts of antibody have been precipitated by toxin and toxoid from individual sera. Evidence is presented that this may have been due to slight differences in antigenic specificity. A serum, Hu, which had been held to contain no precipitating antibody, has now been shown, by the Preer and Oudin techniques, to contain at least 12 microg. of precipitating antibody N (per ml. serum) against an impurity in the toxoid preparation. This estimate has been confirmed by quantitative precipitin determinations. The presence of antibodies to impurities in all human antitoxins examined in the present work brings into question the assumption that human antitoxin as such has a skin-sensitizing capacity.

Immune and allergic reactions to diphtheria toxin and toxoid in guinea-pigs

Guinea-pigs immunized with alum-precipitated diphtheria toxoid (APT) become hypersensitive to diphtheria toxin and toxid. This hypersensitivity is probably due to a mixture of immediate (Arthus-type) reactions and delayed (tuberculin-type) reactions, the former increasing as the level of circulating precipitating antitoxin rose and tending to mask the latter. In a hyperimmune guinea-pig the residual damage following the intradermal injection of toxin is due, at least in part, to hypersensitivity to toxin; toxicity probably contributes relatively little to the extent of the lesion in animals with a high titre of antitoxin.

The technical difficulties of proving the presence of a delayed allergic reaction in animals with an early allergic reaction are discussed.

I am grateful to Dr C. G. Pope, who has been closely associated with this work, not only for providing highly purified materials, but also for his advice.

Toxicity of bacterial exotoxins by the oral route

Reports to the contrary notwithstanding, both tetanus and diphtheria toxins are demonstrably orally toxic. The significance of this finding is considered in relation to the definition of those factors which are determinants of the potency of bacterial protein toxins by the oral route.

The effect of pre- and neonatally injected diphtheria toxoid on the homologous responsiveness of young guinea pigs. A preliminary report

A number of guinea pigs injected prenatally with diphtheria toxoid were found to be incapable of making flocculating antibodies to the antigen after immunization in early adulthood. Several of these animals showed an exaggerated susceptibility to diphtheria toxin.

Multiple diphtheria antigen-antibody systems investigated by passive haemagglutination techniques and other methods

A fair degree of correlation has been found between the in vivo antitoxin content of sera from horses immunized with crude Corynebacterium diphtheriae culture filtrates and the direct agglutinin titre of the sera when tested with sheep cells sensitized with diphtheria toxoid.

Haemagglutination inhibition tests at the L_A level of test with the same sera showed some rather large discrepancies from the in vivo and further tests with special agglutinin inhibiting toxins suggested that specific antitoxin free from other accessory antibodies might be non-agglutinating, and therefore not titratable by haemagglutination inhibition.

The phosphate-stable, pepsin-stable and trypsin-stable antigens isolated from culture filtrates of C. diphtheriae were found to contain extremely small quantities of specific toxoid, and cross titration of each of the three antigen preparations showed that there was very little contamination by other antigens within the group.

Absorption of diphtheria antiserum with red cells sensitized with each of the three accessory antigens individually, showed that the antibodies were highly specific and distinct. Absorption of diphtheria antiserum with a mixture of red cells sensitized with the three different antigens removed all demonstrable accessory antibodies, and the absorbed serum would no longer agglutinate cells sensitized with complete diphtheria toxoid. The absorbed serum, however, retained a large proportion of its neutralizing capacity for diphtheria toxin, when titrated in vivo.

Titration of each of the accessory antibodies in a number of horse sera by haemagglutination inhibition demonstrated a correlation between the values for the accessory antibodies to the phosphate-stable and pepsin-stable antigens, but no correlation with the values for the antibody to the trypsin-stable antigen, when compared with results of the flocculation test.

The relative proportions of diphtheria toxin and of the phosphate-stable and pepsin-stable antigens remained constant at all stages of purification of a filtrate including several recrystallization procedures. However, the concentration of the trypsin-stable antigen declined steadily during the process. The relative proportions of toxin, phosphate-stable and pepsin-stable antigens in several crude culture filtrates were constant under reasonable conditions of storage and very varied where deterioration had occurred. These three antigens also maintained a constant ratio in growing culture, the trypsin-stable antigen did not.