The ligands are generally bound in plasma to a significant extent by several transport proteins (both high and low affinity), irrespective of their endogenous or exogenous origin. The protein binding of endogenous compounds (such as hormones) exhibits higher affinity and specificity than those of exogenous compounds (such as drugs). For plasma proteins that bind the same ligand(s), structural similarities or a common genetic origin may be found, although this is not a general rule. Alterations in ligand binding may be due to modifications of either the structure or the level of the binding protein. These modifications may result from genetic make up, physiology or pathology. In some situations, plasma binding may impair the distribution of drugs to tissues, with drug distribution then mainly restricted to the distribution compartment of the drug-binding protein. In other instances, the plasma drug-binding is permissive, and does not limit drug distribution to tissues. A given drug-transport protein system may have either a permissive or a restrictive effect on the drug distribution, depending on the tissue. The physiological significance of the high-affinity transport proteins is not completely understood. These proteins may increase the plasma concentration of poorly hydrosoluble ligands, ensure a more uniform tissue distribution and increase the life of the ligands. The life of the protein may also be increased by ligand binding. High-affinity transport proteins are also involved in some specific carrier mediated transfer mechanisms. It is possible to demonstrate structure-binding relationships or binding selectivity for the plasma transport proteins, but these are quite independent of relationships observed at the receptor level.
Lymphocyte transformation tests (LTT) to drugs remain widely used in drug reactions, despite controversies about their real usefulness. We tested the lymphocytes of 12 patients recovering from a drug-induced Toxic epidermal necrolysis (TEN). There was no difference between the amounts of thymidine incorporated when patients’ lymphocytes were cultivated with culprit or innocent drugs. In both situations the lymphocytes from patients reacted like the lymphocytes from controls cultivated with the same panel of drugs. These negative results do not exclude that a hypersensitivity reaction may play a role in the physiopathology of TEN. Anyhow, they clearly indicate that testing lymphocyte transformation to drugs has no practical value in the diagnosis of TEN.
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