Staining of serial sections identified a population of mononuclear cells positive for ED-1 (the rat homologue of CD68), T-SYK, and P-SYK (Figure 1d–f, respectively) in diseased lung, and dual staining confirmed T-SYK expression in ED-1+ve cells (Figure 1g), suggesting an infiltrating population of monocytes/macrophages expressing activated SYK at sites of alveolar hemorrhage. Here, CD68 is linked to hemorrhage.