Inhibition of neutrophil apoptosis after elective surgery

Background. Neutrophils play a crucial role in host defense against infecti ons, but their inappropriate infiltration and activation within tissues can cause host tissue damage through release of reactive oxy gen metabolites, metalloproteinases, and proinflammatory cytokines. The termination of a neu trophil-mediated inflammatory response is effected through programmed cell death or apoptosis. Delayed neutrophil apoptosis is associated with proinfl ammatory diseases, such as the systemic inflammatory response syndrome. sur gery induces a profound inflammatory response; therefore, neutrophil apopto sis of patients undergoing elective surgery was investigated. Methods. Nonseptic patients undergoing elective orthopedic surgery while un der epidural anesthesia had neutrophils and platelet-poor plasma isolated f rom whole venous blood harvested at 4 time points: pre-epidural, 45 minutes postepidural but before surgical intervention, 1 hour postsurgical incisio n and 24 hours postsurgery. Neutrophil apoptosis was quantified at 1, 12 an d 24 hours in culture by immunofluorescence flow cytometry of annexin V and propidium iodide staining and confirmed by TUNEL (terminal deoxynucleotidy l transferase nick end labeling) assay for DNA strand breaks. Serum cytokin es were quantified by specific enzyme-linked immunosorbent assay. Results. Spontaneous neutrophil apoptosis after elective surgery was signif icantly (P <.001) inhibited with an effect evident within an hour of surgic al incision and persisting at 24 hours postsurgery. The addition of patient s' 24 hour postoperative plasma to healthy neutrophils markedly (P <.01) re duced neutrophil apoptosis, whereas plasma taken an hour after surgical inc ision was ineffective. Interleukin (IL)-6 runs notably increased (1395 +/- 196 pg/mL, P <.01) 24 hours postsurgery and at this postoperative concentra tion inhibited (P <.01) apoptosis of normal neutrophils. Levels of other in flammatory mediators (IL-1 beta, tumor necrosis factor alpha, granulocyte-m acrophage colony-stimulating factor, soluble Fas, soluble Fas ligand) were unaltered. The anti-inflammatory cytokine IL-10 was only slightly increased 24 hours postsurgery (8.32 +/- 2.99 pg/mL); however, the addition of recom binant human IL-10 (10 ng/mL) counteracted (P <.05) inhibition of neutrophi l apoptosis induced by IL-6 and postsurgery plasma. Conclusions. These results identify marked inhibition of neutrophil apoptos is after elective surgery and suggest that the inhibition of neutrophil apo ptosis in the postoperative period is, at least in part, a result of solubl e circulating factors. The marked imbalance favoring proinflammatory over a nti-inflammatory cytokine release in the immediate postoperative period med iates the overwhelmingly antiapoptotic net capacity of postsurgery plasma.