A strikingly constant ratio exists between Langerhans cells and other epidermal cells in human skin. A stereologic study using the optical disector method and the confocal laser scanning microscope

Langerhans cells play an important part in the immune surveillance of the h uman epidermis. Therefore, a certain distribution and numerical relationshi p to other epidermal cells can be expected. To quantify epidermal Langerhan s cells population extensive studies have been performed using two-dimensio nal quantification methods on vertical sections or epidermal sheet preparat ions. Whereas methods using vertical sections were complicated considerably by the sampling procedure, the dendritic shape, and the suprabasal, nonran dom distribution of Langerhans cells, epidermal sheet preparations have the ir limitations regarding the numerical relationship of Langerhans cells to total epidermal cells and the epidermal morphology as such. In order to imp rove the validity of data the three-dimensional dissector method combined w ith confocal laser scanning microscopy has been applied to quantify the num ber of langerhans cells and other epidermal cell nuclei per volume unit in cryosections of 24 punch biopsies of normal breast skin of eight women. Fur thermore, the ratio of Langerhans cells to other epidermal cells, their num ber per biopsy, and per skin surface area were calculated. To minimize the bias by shrinkage the reference volume was estimated using Cavalieri's prin ciple. A constant ratio of one Langerhans cells to 53 other epidermal cells was identified in breast skin (interindividual correlation coefficient: 0. 952, p<0.0001). Thus, Langerhans cells represent 1.86% of all epidermal cel ls; however, a wide interindividual range was found for the number of Lange rhans cells per mm(2) (912-1806; mean +/- SD 1394 +/- 321) and other epider mal cells per mm(2) (47,315-104,588; mean +/- SD 73,952 +/- 19,426). This e xplains the conflicting results achieved by conventional morphometric asses sments relating cell numbers to skin surface area, ignoring the varying thi ckness of the epidermis. The surprisingly constant relationship of Langerha ns cells to other epidermal cells stresses the hypothesis of an epidermal L angerhans cells unit where one Langerhans cells seems to be responsible for the immune surveillance of 53 epidermal cells.