Leukocytapheresis Changes Functional Characteristics of Circulating Neutrophils in Humans: Mechanistic Implications

Abstract

Background and aim: Postoperative leukocytapheresis (LCAP) reduces surgical site infection (SSI) in ulcerative colitis (UC) patients undergoing proctocolectomy with ileal pouch–anal anastomosis (IPAA). To clarify the effect of postoperative LCAP on circulating neutrophils, we investigated neutrophil function before and after LCAP in UC patients undergoing proctocolectomy with IPAA. Method: Circulating neutrophils were obtained from 29 UC patients undergoing IPAA before and after postoperative LCAP. The phagocytic activity was measured using Escherichia coli BioParticles. Neutrophil viability after co-culture with E. coli was measured by flow cytometry. Inflammatory cytokines in patient serum and supernatants after co-culture of neutrophils with E. coli were measured by enzyme-linked immunosorbent assay. Results: No difference in phagocytic activity was found between preand post-LCAP neutrophils. The percentage of necrotic neutrophils was significantly decreased in post-LCAP neutrophils cocultured with E. coli. Serum neutrophil elastase (NE) after LCAP was significantly increased. No difference in cytokine production was found between pre- and post-LCAP neutrophils cocultured with E. coli. NE and tumor necrosis factor (TNF)-α levels in supernatants of post-LCAP neutrophils cocultured with E. coli were higher in patients with longer operating time and higher postoperative neutrophil count, respectively. Phagocytic activity of post-LCAP neutrophils was lower in the longer operating time group. Serum TNF-α level after LCAP was higher in the SSI group. Conclusion: Postoperative LCAP decreases the subset of circulating neutrophils, which induces necrosis against bacterial infection. This suggests a possible mechanism of prevention of SSI.