Hair cortical cell counts (HCCC), a new sensitive in vivo assay with possible applications for biological dosimetry.

In the region of a growing hair follicle where terminal keratinization takes place, the nuclei of the medulla and cortex are gradually degraded. In the zone between rapid cell proliferation in the matrix and the complete loss of the nuclei in the formed hair, the number of medullary cells in the hair proved to be a sensitive-radiation-dose-dependent endpoint (Potten et al. 1990). Nuclei in the cortex of the hair are similarly degraded but are more difficult to quantitate since they form a circumferential ring of cells round the medulla. However, using the confocal microscope to obtain discrete optical sections just above and below the medulla, the number of cortical cells was reproducibly counted. The maximum reduction in cortical cell count occurred on the 3rd day after irradiation. Here, the dose-response curve (0.5-4.0 Gy) is presented, for the population of cortical cells in awl guard hairs of the mouse for 137Cs gamma-rays at 4 Gy/min, which was exponential with no significant shoulder, (the D0 was 2.4 +/- 0.2 Gy and the extrapolation number 1.2 +/- 0.1). The cortical cells exhibited a slightly higher D0 value than the medullary cells but differed in that there was no evidence of a shoulder. The effects of 0.5 Gy could be detected. The degree of sensitivity, and the fact that cortical cells are readily detected in human hair follicles, unlike the medullary cells, make this a potentially valuable human biological dosimeter.