Changes in the prevalence or incidence of certain diseases over time are likely to provide clues to pathogenesis. While we rheumatologists worry from time to time about the possible disappearance of rheumatoid arthritis (RA), one of our major reasons for getting up in the morning,1 2 our colleagues in the chest and allergy clinics have no such anxieties, presiding as they do over a substantial increase in the prevalence of asthma and other atopic disorders.3 Particularly striking have been the changes, over comparatively short periods of time, in the prevalence of atopic disorders in countries of the former Eastern bloc, particularly East Germany, where relative genetic homogeneity of the populations in the former East Germany and West Germany makes comparisons particularly telling. Thus despite heavy levels of atmospheric pollution in the east, which would have been thought likely to exacerbate respiratory diseases, the prevalence of asthma was found to be considerably higher in the less polluted west.4 A more recent study shows that only four years after the fall of communism, the prevalence of hay fever and atopy were measurably increased in Leipzig schoolchildren.5 The slogan that has emerged from such observations is that, with respect to atopic disorders, “civilisation is bad for you”, civilisation being a synonym for western lifestyle.6 What are the likely reasons for this, and why would they be of interest to rheumatologists?

To explain the rheumatology interest requires a little immunological background. One of the main advances in immunology in the past decade has been the realisation that recognition of antigen by T lymphocyte can lead to quite different outcomes, depending on the set of cytokines made by the responding T cell.7 Two such sets have been defined, and the cells making them termed …