ABSTRACT
ABSTRACT During the last few decades, the prevalence of atopic disease has increased in countries with a Western lifestyle. The hygiene hypothesis states that this increase may be due to a decreased exposure to microbes or microbial products early in life. The evidence for this hypothesis is circumstantial and merely based on data derived from epidemiological studies. During the last few years, the hygiene hypothesis has been questioned repeatedly and a revision of the hygiene hypothesis has been proposed. This revision suggests that a normal development of the immune system requires interaction between the human host and microbes or microbial products. Due to this host-microbes interaction early in life, regulatory T-cells may develop, which prevent immune-mediated disease. The hygiene hypothesis offers new opportunities for prevention of atopic disease, like administration of BCG, M. vaccae, CpGs and probiotics which are recently being developed and tested in animal and human models.
