Immunologically mediated toxicity.

A major consideration which precedes the release of a new chemical into the environment of human beings is the possibility of its producing an undesirable or toxic effect. Toxicity is the clinical end-point of a mechanism which results in tissue damage. One such mechanism is mediated via the immunological system. The effect of some chemicals on immunologically competent cells has been to induce perturbations of immunological competence. This is currently under debate as a toxic hazard, and the concept is explored here, particularly in relation to the action of alkyl tins. Hypersensitivity, which is tissue damage resulting directly from an allergic reaction, depends on a substance acting as an antigen. Since many compounds of toxicological interest have a molecular weight less than 5000, the ability to induce an allergic state is governed in part by factors that influence antigen formation, covalent interactions with macromolecules and metabolism. These factors, together with an analysis of 'immunological specificity', are illustrated by experimental work on practolol, which demonstrates that an antibody present in human sera reacts with a product of first-phase metabolism.