Aetiological role of viruses in multiple sclerosis: a review

Can environmental factors explain the epidemiology of schizophrenia in immigrant groups?

Recent evidence suggests that high rates of schizophrenia in first- and second-generation immigrants could be due to exposure to environmental factors such as viral infections in the host country. These findings are discussed alongside parallel data relating to other diseases such as multiple sclerosis and diabetes mellitus. It is argued that in each case the interaction between the environmental agent and constitutional factors related to the immune system need to be considered.

Substance P and multiple sclerosis

Multiple sclerosis is an inflammatory disease which affects the white matter of the central nervous system (CNS). The aetiology of this condition is unknown but it is generally believed to represent an autoimmunological response to a component of myelin triggered by an environmental factor, in a genetically susceptible individual. The natural history of the disease, in terms of clinical disability, is unpredictable, and the factors responsible unknown. Substance P is an undecapeptide that acts as a neurotransmitter in the CNS and as a regulator of immune responses. The recent discovery of substance P immunoreactive astrocytes in multiple sclerosis plaques raises the possibility that this peptide may be important both in the development of plaques and in governing the natural history of the disease.

MS and SLE in twins of successive generations

During a nationwide twin study on multiple sclerosis (MS) in Finland a dizygotic pair discordant for MS was found. The affected co-twin had dizygotic twin daughters. The affected co-twin of the second generation had systemic lupus erythematosus (SLE). Both pairs were thoroughly examined. No evidence of CNS involvement in the healthy co-twins was found. In pairwise comparisons, virus-specific IgG antibodies to measles and mumps were significantly increased in the MS patient whereas the same was true for rubella in the SLE patient. Both MS and SLE patient expressed HLA alleles most often found to be associated with these disorders. Reversed CD4/CD8 ratios were observed in both MS and SLE patient. No difference in interleukin-2 receptor expression were found but gamma-interferon secretion in the MS patient showed marked increase whereas that of the SLE patient was of the same magnitude as in the healthy members. A different triggering stimulus rather than the dissimilarity in the immunogenetic predisposition may be decisive as to whether or not they develop MS or SLE.