Morphology of the Warthin-Finkeldey giant cells in monkeys with experimentally induced measles.

The lymphoid tissues of 9 monkeys infected experimentally with wild type measles virus were examined by light and electron microscopy. Multi-nucleated giant cells of the Warthin-Finkeldey type were found 7 to 11 days after virus inoculation. The giant cells occurred mostly in the germinal center of lymphatic follicles, where they underwent degeneration and disappeared rapidly. Lymphoid and reticular types of giant cells were recognized. The ultrastructural evidence suggested that some of the nuclei contained in giant cells were formed by an aberrant nuclear cleavage. The majority of giant cells, however, were postulated to arise from virus-mediated cell fusion, although direct evidence of cell fusion was not seen. Peculiar nuclear changes, in which some nuclei and fragments of the outer nuclear membrane were contained in a common outer membrane of the nuclear envelope, were observed in all lymphoid giant cells. Both cytoplasmic and intranuclear inclusions were seen to be composed of viral nucleoprotein strands. The former were detected in all giant cells of both types, and the latter in occasional nuclei, providing the direct evidence that giant cell formation resulted from replication of the virus.