Changes in nucleic acid and protein content in nuclei of human cervical cells

Nuclei in five classes of cervical cells observed in Pap smears were studied using quantitative epifluorescence microscopy. The five classes of cells were: parabasal (Pb) cells; intermediate cells with round (I-R), oval (I-O), and rod-pyknotic (I-RP) nuclei; and, pyknotic (P) cells. Six nuclear traits were measured: total nucleic acid, DNA, RNA, total protein, histone, and non-histone protein. The six nuclear indices increased as Pb cells became I-R cells (cell enlargement and maturation), and then decreased as I-R cells degenerated through the following senescence sequence: I-O----I-RP----P. We infer that these changes continue and result in anucleate, superficial cells. Pb cells are probably in early stages of DNA synthesis (S-phase of the cell cycle) since the mean for DNA increased as they became I-R cells. The following types of cells comprised the Pap smears studied: Pb, 7%; I-R, 19%; I-O, 55%; I-RP, 8%; P, 9%; superficial cells with nuclei devoid of nucleic acids, 1%; and, anucleate cells, 1%. We conclude that cervical exfoliative cytology provides a model system for the study of human cell development, maturation, senescence, and death in addition to its use in detecting early through late stages of cervical cancer. The high correlation between the nuclear indices studied suggests that several quantitative nuclear parameters other than DNA may be useful for cancer detection.