Expression of interleukin-1 alpha, interleukin-6, and basic fibroblast growth factor by cultured skin substitutes before and after grafting to full-thickness wounds in athymic mice

Objectives: Cultured skin substitutes (CSSs), consisting of human keratinocytes and human fibroblasts attached to collagen-glycosaminoglycan substrates, have been demonstrated to cover wounds, and may release detectable quantities of growth factors that promote wound healing. Materials and Methods: Basic fibroblast growth factor (bFGF), interleukin-1 alpha (IL-1 alpha), and interleukin-6 (IL-6) were assayed by enzyme linked immunosorbent assay and immunohistochemistry in CSSs in vitro and at days 1, 3, 7, 14, and 21 after grafting to full-thickness wounds in athymic mice. Measurements and Main Results: When isolated cells were tested, IL-1 alpha was found to come primarily from the keratinocytes, whereas bFGF was from the fibroblasts. Combinations of both cell types in the CSSs resulted in a synergistic enhancement of IL-6 expression, Quantities of all three cytokines from CSSs were greater in vitro compared with in vivo levels at all time points after grafting, bFGF increased from day 1 to day 7, and then remained relatively constant until day 21, At day 3 maximal levels of IL-1 alpha were observed, By day 7, IL-1 alpha decreased to approximately 40% of maximal levels, and subsequently increased until day 21, IL-6 levels were highest at day 7 after grafting, All cytokines had reached elevated levels during the time of wound revascularization (days 3-7). Conclusions: The sequence of cytokine synthesis in the wounds (i.e., rapid IL-1 alpha increase followed by IL-6 expression) parallels serum levels reported after a septic challenge, These findings support the hypothesis that the wound is a source of systemic cytokines.