Fibroblasts in dermal tissue repair. Electron microscopic and immunohistochemical study.

The cellular dynamics of dermal regeneration were studied in nonsutured cutaneous wounds of female pigs and monkeys with electron microscopy and immunohistochemistry to demonstrate the origin and the development of fibroblasts forming granulation tissue. The results indicate that fibroblasts do not originate from histiocytes but from resting fibroblasts in the wound margins. These resting fibroblasts first become undifferentiated mesenchymal cells termed "X" cells. The "X" cells then multiply, migrate, and invade the wound defect in approximately 3 days, transforming into highly active fibroblasts. The active fibroblasts are endowed with the capacity of further transformation to fibroclasts and myofibroblasts. The latter two cell populations then effectively cause remodeling of newly formed tissue and contraction of wound margins.