Environmental pollution and allergy: historical aspects.

It may be a coincidence, but it is a fact that the first clear characterization of hay fever began in England where modern industrialization started in Europe. Only at the end of the 20th century were associations of the increasing prevalence of allergy with outdoor air pollution discussed. The seminal study came from Japan from the group of T. Miyamoto linking the increase in Japanese cedar pollinosis to an increased prevalence of Diesel cars and probably exposure to Diesel exhaust in epidemiological, animal experimental and in vitro studies. In Germany first epidemiological studies were done in North Rhine-Westphalia and Bavaria in 1987 and 1988 showing a striking prevalence of allergic disease of up to 10-20% in preschool children. After German reunification the most surprising observation was a lower prevalence of hay fever in East German children compared to the West, although there was a much higher air pollution with SO2 and large particulate matter. Modern smog as found over West German cities most likely originating from traffic exhaust and consisting of fine and ultrafine particles was shown to be associated with higher incidence rates of allergy and allergic sensitization. In the 10 years after reunification there was a steep increase of allergy prevalence in East German children reaching almost the same level as in West Germany. Obviously, a multitude of lifestyle factors - beyond air pollution - may be involved in the explanation of this phenomenon. Surprisingly the skin manifestation of atopy, namely atopic eczema, was more frequent in East German children compared to the West, thus differing from airway allergy. Meanwhile in vitro studies and animal experiments have shown that a variety of air pollutants mostly from environmental tobacco smoke (indoors) and from traffic exhaust (outdoors) can stimulate immune cells inducing a Th2-dominated response besides their irritative effects. While 50 years ago in allergy textbooks a clear distinction was made between 'toxic' or 'allergic', the newly developed concept of allergotoxicology has stimulated research tremendously, meaning 'the investigation of effects of toxic substances upon the induction, elicitation and maintenance of allergic reactions'.