DEVELOPMENT OF A CLONING ASSAY WITH HIGH CLONING EFFICIENCY TO DETECTINDUCTION OF 6-THIOGUANINE-RESISTANT LYMPHOCYTES IN SPLEEN OF ADULT MICE FOLLOWING IN-VIVO INHALATION EXPOSURE TO 1,3-BUTADIENE

A cloning assay with high cloning efficiency has been developed to det ect spontaneous and induced 6-thioguanine-resistant T-lymphocytes (HPR T mutants) from the spleen of adult mice. The mean cloning efficiency in untreated male mice of 20-22 weeks old was 34.5 +/- 11.2% (SD) and the corresponding mutant frequency 0.7 +/- 0.8 (SD) x 10(-6). The clon ing efficiencies obtained in this study are substantially higher than those reported previously by other investigators. Using this assay, it could be demonstrated that inhalation exposure of mice to 200, 500 or 1300 ppm of 1,3-butadiene for 6 h/day on 5 consecutive days caused a statistically significant induction of 6-thioguanine-resistant mutatio ns in T-lymphocytes from spleens of adult mice exposed to 1300 ppm. Th e exposure to 1300 ppm resulted in a three-fold increase of the sponta neous mutant frequency. The mutant frequency after exposure to 500 ppm was higher than the control but the increase was not significant.