Intracellular distribution of the 15-lipoxygenase in IL-4–treated monocytes. Cell preparation, immunoperoxidase staining, and electron microscopy are described in Materials and Methods. (A) Control monocytes (no IL-4 treatment) incubated with a nonimmune rabbit IgG preparation; 10,500-fold magnification; (B) IL-4–treated monocyte, 9,200-fold magnification. Here the cells were stained with a polyclonal anti–15-LOX antibody (IgG fraction). Arrows indicate the localization of the enzyme at the membranes of subcellular vesicles. Arrowheads indicate the localization at the cytosolic side of the plasma membrane.