Multiple sclerosis and allergic diseases: is there a relationship?

Immune system disorders characterize various diseases such as multiple sclerosis (MS) and allergic diseases (AD). In MS, T-helper (Th)1 cell phenotype is responsible for the disease onset and long-term evolution. On the other hand, excessive Th2 cell activity has been demonstrated in AD. The simultaneous increase of MS and AD in the same geographical areas, observed in recent years, has questioned the mutually exclusive correlation between MS and AD immunopathogenesis supported by the Th1/Th2 paradigm and has moved the interest in understanding possible overlaps. This manuscript aims to discuss the literature, collected over the past two decades, about the association between MS and AD, and both experimental and epidemiological studies have been reviewed. The results do not provide a solid correlation between AD and MS, although experimental studies support the involvement of the same cells and molecules in the immunopathogenesis of both diseases. Further studies, increasing knowledge on the cellular and molecular mechanisms involved in these two disorders, could help to clarify if a positive or negative association links them and provide the possibility for the development of new therapies.