The ‘hygiene hypothesis‘ and the Development of Multiple Sclerosis

Abstract

SUMMARY We review evidence linking inadequate microbial exposure in early life to the development of multiple sclerosis (MS). There is some supportive, but not conclusive evidence for a role of a hygienic environment in early life and MS. Population-level studies of MS are consistent with the hygiene hypothesis but are limited by methodological issues. Late infection with Epstein–Barr virus (EBV) has been prospectively associated with MS and must be incorporated into any model where the hygiene hypothesis is implicated in the development of MS. One possibility is that inadequate microbial exposure in early life contributes to a dysregulated host immune response to EBV. Two areas of particular interest include the potential role for helminthic infection in biasing the human immune response away from the immune profile associated with MS and also the role of microbial exposure in training the development of the EBV-specific immune response.

Early-life hygiene-related factors affect risk of central nervous system demyelination and asthma differentially

“…FCD and asthma were not co‐associated within individuals and there was no association between FCD and family history of allergy or between asthma and autoimmune disorders. These findings are consistent with the overall body of work on MS and asthma , but at odds with the antagonistic T helper type 1 (Th1)–Th2 interpretation of immune responses . However, MS, long considered to reflect Th1 over‐activity , is now thought to also involve up‐regulation of Th17 cells and a defect in thymic natural T regulatory cells .…”

“…The contribution of a hygienic early‐life environment to the development of autoimmune disorders is less clear. More than four decades ago, Leibowitz proposed that people with multiple sclerosis (MS) were more likely to have a ‘high level of sanitation’ in their childhood home , but our recent review of the available data indicates only limited support for this hypothesis.…”