Phagocytosis of apoptotic lymphocytes by oligodendrocytes in experimental autoimmune encephalomyelitis

The alterations in oligodendrocytes in myelin basic protein-induced acute experimental autoimmune encephalomyelitis (EAE) in the Lewis rat were studied using the technique of pre-embedding immunolabelling with the Rip monoclonal antibody, which specifically labels the cytoplasm of the cell bodies and processes of oligodendrocytes. In spinal cord sections of untreated and dexamethasone-treated rats with EAE, we found that apoptotic lymphocytes were phagocytosed by Rip-positive oligodendrocytes as well as by CD11b/c-positive macrophages/microglia and by astrocytes expressing glial fibrillary acidic protein. Morphologically normal lymphocytes were also internalised by these cell type, a phenomenon known as emperipolesis. We suggest that this phenomenon represents the phagocytosis of lymphocytes that have undergone the plasma membrane alterations of apoptosis without yet manifesting the nuclear condensation of apoptosis. We also found an increase in the number of clusters of two to four oligodendrocytes, mainly in the grey matter, suggesting proliferation of cells of the oligodendrocyte lineage.