An in vitro test for the diagnosis of delayed allergic reactions to drugs

Introduction. - The adverse effects caused by drugs are classified as toxic, pharmacological or allergic. Allergic side effects are hypersensitivity reactions that involve antibodies (immediate hypersensitivity reactions) or T lymphocytes (delayed hypersensitivity). We describe the results of a study evaluating an in vitro method using peripheral blood T lymphocytes for the diagnosis of erythematous drug-induced delayed hypersensitivity reactions. Materials and methods. - Three groups of patients were included: Group A, patients allergic to amoxicillin (N = 14); Group B, patients who tolerate amoxicillin without side effects (N = 5); and Group C, patients who had developed a non-allergic type of reaction to amoxicillin (N = 10). The diagnosis of allergic reactions (Group A) was demonstrated by a positive skin test reaction 48 to 96 hours after applying amoxicillin to the skin. The lymphocyte transformation test (LTT) and the Elispot test for IFN-gamma were done simultaneously. Ceftriaxon served as the negative control reagent for both the skin and in vitro tests. Results. - The results observed for the L77 indicated a level of sensitivity of 71% when the stimulation index (SI) was greater than 2.5. Under the conditions used, the results of the IFN-gamma assay demonstrated the presence of specific T lymphocytes in Group A with a mean of 70 spots/I 10(6) cells in the presence of amoxicillin, whereas re-stimulation of the cells with the antibiotic control, ceftriaxone, resulted in no IFN-gamma secretion. After stimulation with amoxicilln, 12 out of the 14 patients in Group A had a significantly increased number of spots in comparison with ceftriaxone. Discussion. - These results demonstrate that the Elispot IFN-gamma in vitro assay provides a method to estimate the number of amoxicillin-specific T cells in peripheral blood. This test appears to differentiate patients who are allergic to drugs from those who are not. The test is interesting because it is simple to carry out, a large number of drugs can be tested at the same time, and the results are obtained rapidly. If these results can be confirmed with other drug molecules, then the ELISPOT IFN-gamma in vitro assay could be included in the battery of in vitro tests for delayed hypersensitivity reactions to drugs. (c) 2005 Elsevier SAS. Tons droits reserves.