Detection of fibrocytes in human skin wounds and its application for wound age determination.

Fibrocytes, a newly identified cell type, are bone marrow-derived mesenchymal progenitors that coexpress hematopoietic cell antigens and fibroblast products. In this study, a double-color immunofluorescence analysis was carried out using anti-CD45 and anti-collagen type I antibodies to examine the time-dependent appearance of fibrocytes, using 53 human skin wounds with different wound ages (group I, 0-3 days; group II, 4-7 days; group III, 9-14 days; and group IV, 17-21 days). In wound specimens with an age of less than 3 days, CD45+/collagen type I+ fibrocytes were not detected. The fibrocytes were initially observed in wounds aged 4 days, and their number increased in lesions with advances in wound age. In a semiquantitative morphometrical analysis, the average number of fibrocytes was highest in the wounds of group III. These findings imply that human skin wounds containing fibrocytes are at least 4 days old. Moreover, a fibrocyte number of over 10 indicates a wound age between 9 and 14 days (i.e., group III). Based on the average number of fibrocytes in each group, a fibrocyte number of over 15 more strongly suggests a wound age of 9-14 days. Together, our observations indicate the participation of fibrocytes in wound healing of human skin inducing the accumulation of extracellular matrix components, and therefore, detection of fibrocytes could be a useful marker for wound age determination.