Phenotypic and functional characteristics of macrophages differentiated in endotoxin-containing environment

Objective To further understand the macrophage heterogeneity in the infection and inflammation, we characterized the phenotype and functional behavior of human monocytes differentiated in endotoxin (LPS)-containing cultures. Methods Purified human peripheral monocytes were cultured with medium containing 1μg/ml of LPS. Their ultrastructure, expression of membrane antigens and production of superoxide and the cytokines were determined at various stages of their differentiation. Results Monocytes cultured with LPS underwent substantial changes in morphology similar to that observed when monocytes differentiated into macrophages. However, they exhibited different functional behavior from macrophages matured in autologous serum. The expression of HLA-DR was up-regulated in these cells at day 1 of culture, and down-regulated at day 5. Superoxide production in response to phorbol myristic acetate was maintained in LPS cultured macrophages, but declined with time in cells cultured with serum. Spontaneous secretion of tumor necrosis factor-α and interleukin-1β was higher in macrophages developed in LPS compared with those matured in serum. Conclusion Human monocytes maintained in LPS-containing cultures exhibit differentiation-associated activation phenotype, which differs from that of normal monocyte-derived macrophages, characterized by decreased MHC classⅡ antigen expression and higher capacity for generation of proinflammatory mediators.