Abstract
Summary
The ability of a lymphoid cell population to be stimulated to incorporate radio-labeled thymidine by phytohemagglu-tinin (PHA) has been widely accepted as a ready measure of cellular immune competence. Persisting PHA responsiveness in lymphocytes from irradiated blood, in particular, has been taken as evidence that radiation does not protect against the hazard of graft-versus-host reaction (GVH) in blood transfusion. Our independent conclusion that radiation of blood under appropriate conditions does protect immunologically incompetent recipients against GVH made necessary an effort to resolve this apparent contradiction. Irradiated cells stimulated with either PHA or allogeneic leukocytes have been studied in terms of known radiation sensitivity curves for cellular proliferation. These studies permit the conclusion that PHA responsiveness is not a valid measure of the immunocompetence of irradiated cells. Since the ability to replicate seems much more radiosensitive than the ability to respond, tests such as PHA responsiveness which measure only the ability to recognize and react to a mitogenic stimulus lose their validity in this context.
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