The measles virus is very difficult to grow, although it can be grown in primary human or monkey kidney cell cultures. The isolates can be adapted for growth on HeLa or Vero cell lines. Characteristic cytopathological effects include multinucle-ated giant cells with cytoplasmic and nuclear inclusion bod-ies. Warthin–Finkeldey cells are the multinucleated giant cells produced by measles virus in lymphoid tissue of the patients. These giant cells are produced as a result of the F proteins in the spikes.