Diagnosis of drug allergy by the lymphocyte stimulation test with the MTT [3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay.

The lymphocyte stimulation test (LST) is one of the most useful laboratory tests for the identification of allergy to a specific drug. The present study was conducted to examine utility of the LST using the [3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) assay as a method for diagnosing drug allergy. The basic experimental conditions for the MTT assay were determined by using CTLL cells from human T-lymphoma, dependent on IL-2, and human peripheral blood lymphocytes. The amount of MTT needed was 0.5 mg per well and the peak maximum of MTT formazan was close to 565 nm. The blastogenesis of the lymphocytes was expressed as a Stimulation Index (SI). The value of the SI was almost constant at cell numbers ranging from 5 x 10(5) to 1 x 10(6) cells/ml. The SI of some drugs using normal peripheral blood lymphocytes was less than 1.3. We used the MTT assay in the LST to examine the allergenicity of 83 drugs which were used in 43 cases of suspected drug-induced hepatitis. The range of SI was 0.92-2.02. An SI of 1.2 or more was seen in 62.8% of cases, 1.3 or more in 51.2% of cases, and 1.4 or more in 41.9% of cases. There were 26 drugs with SI greater than 1.3. Seven of these were antibiotics, while the rest included antihypertensives, analgesics, psychotropics, antiallergics and antiepileptics. This method is extremely well suited for the diagnosis of drug allergy in a clinical situation. The greatest benefit of the MTT assay is that the complete test procedures can be carried out in a general laboratory.