Retrospective comparisons of the prevalence and age, where appropriate, of some childhood infectious illnesses and vaccinations, together with serological evidence for exposure to 16 viruses, many of which have previously been implicated in the aetiology of multiple sclerosis (MS) were made in 177 patients with acute optic neuritis, other recent isolated demyelinating episodes or established MS and 164 controls. The expected high frequency of HLA-DR2 in patients with demyelinating disease was matched by preselection of normal controls with this antigen (DR2+); the remaining individuals were classified as HLA-DR2 negative/DR3 positive (DR3+) or HLA-DR2 and 3 negative (DR2/3 -). Cases were compared with controls, collectively and in analyses restricted to each genetic group; these comparisons were repeated considering the three categories of patients with demyelination and two control populations separately. All DR2+, DR3+ and DR2/3 - individuals were compared in a single analysis to assess the effect of HLA type itself on the results. Patients with demyelinating disease had rubella and measles at a later age and reported mumps infection more frequently than controls. Age of typhoid vaccination and duration of exposure to domestic dogs was higher in all cases than controls. Age of measles and mumps, but not rubella, was higher in DR2+ cases than controls; but differences were not observed in the other genetic groups. Higher rubella antibody titres were present in all cases than controls and in analyses confined to DR2+ individuals in whom higher Epstein Barr virus antibody titres were also present. Measles haemagglutination inhibition and parainfluenza I antibody titres were increased and influenza A antibodies detected less frequently in all patients with optic neuritis and those with DR2 compared with appropriate controls; influenza B antibody titres were lower in all DR2+ cases than controls. Higher adenovirus and varicella zoster antibody titres were present in DR2/3- patients with demyelination and other neurological diseases compared with normal controls. Overall, older age of infection and higher antibody titres were observed more often in patients with optic neuritis, in particular DR2+ cases, than other individuals with demyelination or controls. Our serological results are consistent with the presence of abnormal HLA-immunological reactivity in patients with MS but cannot be explained only by an effect of DR type itself; age at which susceptible individuals develop some common childhood infections may also influence the subsequent development of the disease.

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