Objective-To test the hypothesis that smoking increases the risk of sensitisation by occupational allergens.Design-Historical prospective cohort study. IntroductionAbout 5-10% of the population has asthma, and a recent report from the Tucson longitudinal study suggests that IgE dependent allergic mechanisms are important in asthma at all ages.' Little is known about the aetiology of asthma and that of related allergic conditions, such as hay fever, but studies of asthma induced by occupation are likely to be informative because occupational exposures are important "natural experiments." Smoking seems to promote the development of asthma and of specific IgE antibody in occupational settings.2-4 These studies, including our previous study of workers exposed to tetrachlorophthalic anhydride,! were cross sectional and possibly subject to survivor bias. We now report a longitudinal study in the platinum refining industry of the development of respiratory symptoms and of responses to platinum salts on skin prick testing in relation to smoking habit and atopic state.Charged halogenated platinum salts stimulate an IgE response", and cause allergic asthma. They are intermediates in the process of refining platinum, a corrosion resistant metal used as a catalyst and in jewellery. 9 In the past workers in refineries had a high

A series of platinum complexes has beeti used for allergy tests in a tiumber of platinum refinery workers who are known to be sensitive to hexachloroplatinate ([PtCl(,]^^) salts. The results show that the allergy-eliciting compounds are confined to a very small group of ionic complexes containing reactive halogen ligands. Neutral complexes and those containing more strongly bound ligands are totally inactive. These variations in activity are interpreted in terms of established kinetic and thermodynamic parameters.

Summary A RAST has been developed for the measurement of IgE antibodies specific to platinum chloride complexes in sensitized workers. Human serum albumin covalently linked to Sepharose beads by the cyanogen bromide method was reacted with ammonium tetrachloroplatinite (II) (NH4)2PtCl4. This conjugate was more suitable for the RAST, than conjugates of HSA and the platinum salt prepared in solution and then linked to the activated Sepharose, showing better sensitivity and giving lower levels of non‐specific uptake of IgE from sera of non‐exposed subjects with high total levels of IgE, e.g. allergic bronchopulmonary aspergillotics.

Sixteen workers, from a platinum refinery, with respiratory disease were tested with solutions of complex salts of platinum and ten gave immediate prick test reactions to concentrations of 10"*-10"* and immediate nasal reactions in seven out of eleven tested to concentrations of IO~^-1O'\ Occupational-type exposure inhalation tests to the dust from mixtures of 40 mg of the platinum salt with 1 kg of lactose gave immediate asthmatic reactions in eight and in one of these a late reaction, all also giving immediate prick test reactions. The asthmatic reactions were inhibited by disodium cromoglycate. In two with negative prick tests, late asthmatic reactions were elicited. The occupational-type exposure test provides a safe, acceptable procedure for etiological diagnosis.

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