Age-related alterations in the inflammatory response to dermal injury.
Previous studies have documented that the ability to heal wounds declines with age. Although many factors contribute to this age-associated deficit, one variable that has not been carefully examined is leukocyte recruitment and function in wounds. This investigation compares the inflammatory response in excisional wounds of young (age 8 wk) and aged (age 22 mo) mice. In the early inflammatory response, neutrophil content of wounds was similar for both aged and young mice. In contrast, macrophage levels were 56% higher in aged versus young mice (81 +/- 20 vs 52 +/- 13 cells per mm2). In the later inflammatory response, wounds of aged mice exhibited a delay in T cell infiltration, with maximum T cell levels at day 10 in aged mice versus day 7 in young mice. Despite this delay, the eventual peak concentration of T cells was 23% higher in the wounds of aged mice (152 +/- 11 cells per mm2 vs 124 +/- 21cells per mm2). The observed alterations in inflammatory cell content suggested that chemokine production might be altered with age. An elevation of monocyte chemoattractant protein (MCP-1) levels was observed in wounds of aged mice. RNase protection studies, however, revealed that the production of most chemokines, including MIP-2, MIP-1alpha, MIP-1beta, and eotaxin, tended to decline with age. Because optimal wound healing requires both appropriate macrophage infiltration and phagocytic activity, phagocytosis was examined. Compared to young mice, wound macrophages from aged mice exhibited a 37%-43% reduction in phagocytic capacity. Taken together, the data demonstrate age-related shifts in both macrophage and T cell infiltration into wounds, alterations in chemokine content, and a concurrent decline in wound macrophage phagocytic function. These alterations may contribute to the delayed repair response of aging.