N. J. Galbraith1, S. P. Walker1, S. A. Gardner1, J. V. Carter1, S. Manek1, S. Galandiuk1, H. C. Polk1 1University Of Louisville,Department Of Surgery,Louisville, KY, USA
Introduction:
Some patients who suffer major infection or trauma respond with an exaggerated compensatory anti-inflammatory response. The purpose of this study was to study monocyte function of patients with surgical infection, and determine the expression of negative regulators of toll-like receptor signaling. .
Methods:
Monocytes were isolated following phlebotomy after written informed consent in colon and rectal surgery patients diagnosed with deep surgical site infection. Samples were studied for baseline parameters of monocyte function, including HLA-DR, and immune response was studied by ex-vivo lipopolysaccharide (LPS) stimulation (100 ng/mL) for 4h. At 4 h, levels of HLA-DR and cytokine responses determined by flow cytometry (FACS) and ELISA, respectively. Monocyte gene expression of negative regulators including suppressor of cytokine signaling 3 (SOCS3), interleukin-1 receptor-associated kinase M (IRAK-M), Src homology region 2 domain-containing phosphatase-1 (SHP-1), and A20 (TNFAIP3, Tumor Necrosis Factor, Alpha-Induced Protein 3) were measured by qRT-PCR. Follow-up samples from the same patients were obtained after resolution of the infection where possible. Healthy controls were studied for comparison.
Results:
Sixteen patients with deep surgical site infection were studied, the majority of which were diagnosed with intra-abdominal abscesses and who were hemodynamically stable at the time of sampling. Ten healthy controls were included for comparison. Baseline monocyte HLA-DR expression was similar between patients and healthy controls, but patients with deep surgical site infection had a lower HLA-DR expression in response to LPS (p<0.05). Infected patients had a suppressed TNF-α production when compared against healthy volunteers (p<0.05). In contrast, infected patients had higher levels of circuiting plasma IL-10 levels (p<0.05).
Of the negative regulators studied, IRAK-M was the most consistently up-regulated in infected patients as compared to healthy controls (p<0.05). Interestingly, the expression of IRAK-M partially returned to the levels of healthy controls following clinical recovery from infection.
Conclusion:
In this study, patients with deep surgical site infection have lower levels of HLA-DR and TNF-α following LPS stimulation, suggestive of impaired cytokine responses and antigen presenting function. IRAK-M, a negative regulator of TLR signaling, was up-regulated in patients during infection, with a partial return to normal levels following clinical recovery. IRAK-M may play a role as a biomarker in identifying “high risk” patients.