Transfer of delayed and Arthus sensitivity with blood plasma from x-irradiated guinea-pigs.

Lethal X-irradiation of sensitized guinea-pigs failed to release a mediator of delayed-type hypersensitivity into plasma in sufficient concentration to effect passive transfer of reactivity to tuberculoprotein or hen ovalbumin. But plasma from such animals did sensitize recipients for an Arthus reaction; and some of this early inflammation, both in actively and passively sensitized subjects, was still apparent at 24 hours. The significance of these late reactions is discussed in relation to the problem they pose when attempting to demonstrate a mediator of delayed-type hypersensitivity.