Abstract

Serum from an individual with occupational asthma from nickel sulphate inhalation was shown by ammonium sulphate (Farr) and anti-IgG coprecipitation tests to contain antibodies which bind 63Ni2+. This binding was absent from 30 control sera. Ligand competition studies with serum and plasma from the propositus and controls are described, and include serial additions of HSA, L-histidine, EDTA, and the tripeptide gly-gly-L-his. The results, like those from metal ion blocking experiments, clearly showed that the formation of the reactive antigenic determinant depends on the selective binding of Ni2+ at the native Cu2+/Ni2+ transport site of HSA. Corroborating evidence is derived from the similar dependence on pH of the Ni2+-HSA formation and the ammonium sulphate 63Ni2+ coprecipitation reactions.