Mechanisms of enhanced prevalence of asthma and atopy in developed countries.

Atopy--a T helper 2 cell driven hypersensitivity to innocuous antigens (allergens) which causes most cases of asthma-- is of complex genetic and environmental origins. There is compelling epidemiological evidence for a rise in atopic disease in 'westernised' communities. The changing pattern of microbial exposure in early childhood is suggested to be the principal candidate mechanism for this rise.