The fine structure of the CNS in multiple sclerosis. I. Interpretation of cytoplasmic papovavirus-like and paramyxovirus-like inclusions.

During an electron microscopic study of the white matter in multiple sclerosis (MS), spheroidal reticular particles were found both in MS and in control brains. These particles have previously been described in the brain in MS and in brain-derived cell cultures in subacute sclerosing panencephalitis. In both cases they were interpreted as papovaviruses, but in size, morphology and distribution they are identical to the reticulosomes and related particles which occur as proteinaceous artefacts in a variety of tissues and in subcellular fractions. Inclusions in endothelial cell cytoplasm, previously reported from the CNS in MS as paramyxovirus similar to measles, have also been found in the present study. The were present both in MS and in control brains and are identified as "rod-shaped tubular bodies", normally occurring organelles of endothelial cells. The necessity for a cautious interpretation of virus like inclusions in emphasized.