According to the so-called hygiene hypothesis [7] , modern living conditions in the industrialised nations isolate infants and children from many infectious challenges that are required for the development of appropriate immunoregulatory networks. This hypothesis has been advanced to explain the rise in incidence of disease associated with immune dysregulation, including asthma, allergy, autoimmunity and at least some forms of cancer, in the industrially developed world [7] . In addition, the hypothesis suggests strategies for interventions for the prevention of such diseases, as illustrated by studies on the epidemiology of malignant melanoma which indicate that certain vaccinations, BCG, vaccinia and yellow fever, can substitute for the significant protective effect of natural B. Krone infections [8 -11] . As epidemiological investigations on MS strongly indicate that this disease is likewise affected by hygiene-related factors and by a history of infections [3, 6] , the challenge is to determine whether there is an underlying distortion of immune responses in this complex disease that could be prevented or corrected by therapeutic intervention.