The LTT is the most extensively studied and widely used in vitro diagnostic test for drug, food and environmental allergies. The method was first used back in the early 1960s to evaluate hypersensitivity reactions to phenytoin and sulfa drugs. The test involved tedious visual counting of mitotic figures until Vischer. adopted measuring radio-labelled thymidine incorporation into cellular DNA as a reflection of cell division rate. Drug specific T-cell clones can be isolated and cloned in vitro and they respond to incubation with the culprit drug with proliferation and expression of certain surface markers.
