Dose-response curve of 12- and 15-HETE formation by murine peritoneal macrophages on IL-4 concentration. Peritoneal lavage cells were prepared from 30 mice by rinsing the peritoneal cavity of each mouse with 10 mL of PBS. The lavage fluid was pooled, the cells were washed once, plated in 6-well plates, and the macrophages were allowed to adhere overnight. After removing nonadherent cells, different concentrations of IL-4 were adjusted and the cells were kept in culture for additional 3 days. For most IL-4 concentrations, three separate wells were used. After 3 days the cells from each well were obtained separately and the arachidonic acid oxygenase activity was determined. 12- and 15-HETE formation was quantified by RP-HPLC. The n-numbers above the traces indicate how many wells were used for one IL-4 concentration, and the arrow bars represent the standard deviation. At 100 pmol/L of IL-4 we measured exactly the same 15-HETE formation in both HPLC runs. Thus, no arrow bar can be given.