Koilocytes are squamous epithelial cells that have nuclei with dense, hyperchromatic, condensed chromatin surround by a clear space. These cells have been described as having the appearance of a raisin. Koilocytes are the characteristic cytopathic effect of HPV. These changes are present in biopsy specimens from the cervix, but they can also be seen in Pap smears from the cervix where these abnormal dysplastic cells have a characteristic increased nuclear/cytoplasmic ratio. Ref:- Harsha Mohan textbook of Pathology