Memory of Past Exposure to the Chemokine IL-8 Inhibits the Contraction of Fibroblast-Populated Collagen Lattices

Abstract

The inflammatory cytokine makeup of healing wounds helps delineate the phases of the repair process. As an example, during the lag phase (inflammatory phase) of repair, elevated levels of IL-8, a chemokine, participate in the activation and chemotaxis of neutrophils. During the normal proliferative and remodeling phases of repair, IL-8 levels are minimal. Healing burn wounds often have small, open, slow-to-heal areas, which have been shown to contain elevated levels of IL-8. Does a limited exposure of IL-8 to fibroblasts in vitro at the concentrations measured in these unhealed sites cause altered cell behavior? To study this possibility the fibroblast-populated collagen lattice (FPCL) model, an in vitro model of wound contraction, was used to investigate fibroblast response to IL-8. As previously reported, the chronic exposure of fibroblasts to IL-8 at 30 ng/ml within FPCLs significantly inhibited FPCL contraction. Fibroblasts in monolayer culture were incubated with IL-8 for 3 days. In the absence of IL-8, FPCLs were manufactured with these preexposed cells and it was found that FPCL contraction was inhibited. Fibroblasts retained their reduced capacity of reorganizing collagen fibrils when previously exposed to IL-8. Treating fibroblasts in monolayer with IL-8 for only 1 h prior to their incorporation into collagen lattices caused inhibition of FPCL contraction. The speculation is that in vivo open areas in reepithelialized healed burns are the consequence of the local population of fibroblasts having been exposed to elevated levels of IL-8. Such an earlier exposure triggers a memory in this population of fibroblasts that alters their capacity to lay down an extracellular matrix that optimizes the migration of epidermal cells.