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Distinct Temporal Patterns of Macrophage-Inflammatory Protein-2 and KC Chemokine Gene Expression in Surgical Injury1

In the present study the regulation of CXC chemokine expression was evaluated in full-thickness abdominal wounds in mice. During the first 24 h after injury, IL-1αβ, KC, macrophage-inflammatory protein (MIP)-2, and monocyte chemoattractant protein-1 were the predominant cytokines and chemokines produced; TNF-α was not detected. Chemokine mRNA expression and protein secretion occurred in two temporal stages. The first, which reached a maximum at 6 h, was associated with high levels of IL-1α and KC and low levels of MIP-2. This stage could be reproduced by intradermal injection of IL-1α or IL-1β and was partially blocked by injection of neutralizing Ab against IL-1α but not IL-1β. In animals depleted of circulating neutrophils, chemokine expression was reduced by nearly 70% during this stage. In the second stage, which peaked at 24 h after injury, modest but significant levels of IL-1β were detected in association with low levels of KC and high levels of MIP-2. This pattern of chemokine expression could not be mimicked by injection of IL-1α or IL-1β (even with prolonged exposure), although MIP-2 expression could be partially inhibited by intradermal injection of neutralizing Ab against IL-1β. Surprisingly, neutrophil depletion before injury resulted in sustained high levels of both KC and MIP-2 expression. These observations demonstrate that these two closely related chemokines are under distinct regulatory controls in vivo that are likely to reflect the temporally ordered participation of different cell types and/or extracellular stimuli and inhibitors.