Upregulation of murine macrophage 12-lipoxygenase activity by IL-4. Murine peritoneal macrophages were prepared as described in Materials and Methods. After adhesion to plastic dishes they were cultured for 4 days in the absence (lower trace) or presence (upper trace) of IL-4 (0.8 nmol/L final concentration). Cells were obtained, and cell homogenates were incubated with arachidonic acid (100 μmol/L final concentration). Product preparation and RP-HPLC as described in the legend to Fig 1. Left inset, enantiomer analysis (chiral phase HPLC) of 12-HETE prepared by RP-HPLC; right inset, ultraviolet-spectra of the products coeluting with 12- and 15-HETE. In some experiments the ulraviolet-spectrum of the products coeluting with 15-HETE did show an absorbance at 280 nm, which may be due to the formation of conjugated ketodienes.