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.