In vitro characterization of possible mechanisms underlying the selective in vivo accumulation of the PCB metabolite 4,4'-bis(methylsulphonyl)-2,2',5,5'-tetrachlorobiphenyl in the lung.

In vivo, the polychlorinated biphenyl (PCB) metabolite 4,4'-bis(methylsulphonyl)-2,2',5,5'- tetrachlorobiphenyl--(MeSO2)2TCB--selectively accumulates in the Clara cells of the bronchiolar epithelium and in the secretory contents of the bronchiolar lumen. In vitro characterization of the interaction of tritiated (MeSO2)2TCB with the lung suggests that this selective accumulation is due to the presence of a secreted ([3H]MeSO2)2TCB-binding protein in the respiratory tract of rats, mice and man. The protein appears to be an almost globular, low-molecular-weight acidic protein which binds ([3H]MeSO2)2TCB and certain other methylsulphonyl PCBs with high affinity. Because of the pathway outlined for accumulation, it is suggested that methylsulphonyl PCBs should be included in studies designed to elucidate the mechanism(s) of PCB-induced lung toxicity.