Monitoring Neutrophil-Expressed Cell Surface Esophageal Cancer Related Gene-4 after Severe Burn Injury

Abstract

Background: We identified recently esophageal cancer related gene-4 (ECRG4) as a candidate cytokine that is expressed on the surface of quiescent polymorphonuclear leukocytes (PMNs) and shed in response to ex vivo treatment with lipopolysaccharide. To investigate the potential biologic relevance of changes in cell surface ECRG4 in human samples, we performed a pilot study to examine a population of burn patients in whom blood could be analyzed prospectively. We hypothesized that cutaneous burn injury would alter cell surface expression of ECRG4 on PMNs. Methods: Patients admitted with more than 20% total burn surface area (TBSA) (n = 10) had blood collected at the time of admission and weekly thereafter. For comparison, blood was obtained from a control group of healthy human volunteers (n = 4). We used flow cytometry to measure changes in ECRG4 + PMNs from patients during recovery from injury. Esophageal cancer related gene-4 expression at each time point was compared with the patient's clinical status based on a Multiple Organ Dysfunction (MOD) score. Results: Esophageal cancer related gene-4 was detected on the PMN surface of cells collected from healthy volunteers, however, within 48 h of admission after burn injury (n = 10 patients), the number of PMNs with cell surface ECRG4 was decreased. Esophageal cancer related gene-4 expression in PMNs was re-established over the course of patient recovery, unless complications occurred. In this case, the decrease in cell surface ECRG4 + PMNs preceded the clinical diagnosis of infectious complications and was reflected by increased organ injury scores. Conclusion: From a small sample set, we were able to determine that PMN cell surface ECRG4 expression was decreased after burn injury and returned to baseline during recovery from injury. Although larger studies are needed to define the role of ECRG4 in human PMNs further, this report is the first assessment of cell surface ECRG4 protein in a patient population to support analogous findings in animal studies.

ECRG4 regulates neutrophil recruitment and CD44 expression during the inflammatory response to injury

“…6E and 5, G and I) and restores homeostatic expression levels. This model is further supported by studies of human burn patients, where it has been observed that cell surface ECRG4 on circulating leukocytes diminishes after injury but returns to housekeeping levels as patients recover (24). These findings support a role for ECRG4 as a sentinel factor, which can both precondition the responsiveness of leukocytes through its regulation of CD44 expression and respond to environmental cues to mediate the kinetics of the cutaneous inflammatory response.…”

“…In murine tumor models, the ability of soluble ECRG4 to increase the recruitment of inflammatory cells is dependent on thrombin cleavage (17). In humans with severe burn injury, ECRG4 is shed from circulating neutrophils, while restoration of cell surface ECRG4 expression correlates with recovery (24). These observations suggest that ECRG4 has a role in regulating specific inflammatory responses, although its function in injury has not been determined in ECRG4 knockout (KO) mice.…”

“…Recent studies indicate that it may promote leukocyte recruitment, with its down-regulation in cancer contributing to escape from immunosurveillance (17,22). ECRG4 physically associates with TLR4 (23), while proteolytic processing releases it from the cell surface (17,24). Soluble ECRG4 binds various scavenger receptors, including LOX-1 (25), and regulates phosphorylation of the nuclear factor B (NF-B) transcription factor (16,23).…”