Distinct regulation of IL-8 and MCP-1 by LPS and interferon-γ-treated human peritoneal macrophages

Background. Interleukin-8 and monocyte chemotactic protein-1 (MCP-1) are major leukocyte chemoattractants during bacterial peritonitis by recruiting neutrophils and monocytes/macrophages respectively. Methods. Peritoneal macrophages (PM) from 12 different CAPD patients with peritonitis were stimulated with either 10 ng/ml LPS, 10 ng/ml IFN-gamma or LPS+IFN-gamma, and IL-8 and MCP-1 production was determined on protein and mRNA levels by using ELISA technique and Northern blot analysis. To obtain information from two different stages of activation, experiments were done with highly activated PM directly after isolation and with cells after 10 days in culture, each group being stimulated for 4h. Unstimulated cells served as control. Results. Immediately after isolation IL-8 mRNA-expression and synthesis was high and could be further increased by LPS stimulation, whereas IFN-gamma treatment showed no significant influence. The levels of MCP-1 were also initially high but could not be further stimulated by LPS, whereas addition of IFN-gamma, resulted in a significant rise in MCP-1 synthesis. After 10 days in culture LPS-stimulation of cells again revealed a significant increase in IL-8 protein synthesis, whereas IFN-gamma showed no effect. LPS anergy for MCP-1 was still seen in PM after 10 days in culture, and IFN-gamma, treatment again induced a significant rise in MCP-1 synthesis. The overall production of both chemokines was far higher on day 1 compared to day 10. Conclusion. Our data show differences in LPS/IFN-gamma regulation for IL-8 and MCP-1 in both highly activated and in resting, mature peritoneal macrophages, suggesting distinct pathways for these chemokines that may offer a means of control for the specific recruitment of neutrophils and monocytes/macrophages in bacterial peritonitis.