Kinetics of epidermal Langerhans cells.

Langerhans cells are considered to play an important role in the initiation of the immune response. This study was performed in order to analyze the kinetics of the Langerhans cell population under different experimental conditions. Using tritiated thymidine, the number of labeled Langerhans cells (demonstrated by the Leucinaminopeptidase reaction), and of labeled basal keratinocytes was investigated by autoradiography in guinea pig skin in vivo, before and 2, 5 and 8 days after stripping and before and 2, 5 and 8 days after initiation of repeated topical exposures to a 0.25% solution of dinitrochlorobenzene (DNCB). In addition the total number of Langerhans cells per mm2 was determined before and after DNCB treatment of epidermal guinea pig sheet preparations using the ATPase reaction. A total of more than 100,000 cell as of basal keratinocytes was stimulated significantly (by statistical analysis), both by stripping and by application of DNCB. After stripping, however, the increase of the Langerhans cell turnover was found to be secondary to the turnover of basal keratinocytes, whereas after DNCB application the increase in the proliferative activity of Langerhans cells appeared as the primary event in epidermal cellular kinetics.