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.