Researchers working to identify diagnostic biomarkers have found several factors that are associated with clinical outcome, including elevated levels of βcatenin, matrix metalloproteases (MMPs), and microbiome complexity in nonhealing wounds (Eming et al., 2014). However, the search for a biomarker signature that can accurately and robustly predict healing outcome remains elusive. Taking cues from recent literature identifying abnormal macrophage behavior in diabetic ulcers (see, eg, Miao et al., 2012; Mirza et al., 2014), we set out to determine whether this finding could be applied to identify a healing signature. Macrophages are the central cells of the inflammatory response and are recognized as primary regulators of wound healing (Koh and DiPietro, 2011). Macrophages exist in a spectrum of functional phenotypes ranging from proinflammatory, or “M1”, to antiinflammatory and prohealing, or “M2”, each orchestrating events specific to the stage of repair (Mosser and Edwards, 2008). Several studies have shown that wound macrophages undergo a phenotypic shift from M1 to M2 during the normal process of cutaneous wound healing, and that this transition is defective in diabetic ulcers (Mirza et al., 2013; Wood et al., 2014). Thus, we hypothesized that temporal changes in the relative expression of proinflammatory and antiinflammatory genes might be useful in distinguishing between healing and nonhealing chronic diabetic ulcers.

Diabetic patients, recruited from Drexel University Wound Healing Center, provided written consent in compliance with the study protocol approved by Drexel University Institutional Review Board (please see Supplementary Materials and Methods for study design and methods). In a pilot study of 10 patients with chronic diabetic foot ulcers, we measured the longitudinal expression of four proin-