Analysis by Northern blot of iNOS mRNA expression. Total RNA was extracted, and 10 μg of each sample was electrophoresed. The Northern blot transfer was hybridized with the specific murine macrophage iNOS cDNA probe (950 bp 5′-end fragment), and an actin probe was used as control for RNA expression. (A) iNOS RNA expression in spleen cells from control mice on day 7 after grafting with syngeneic bone marrow (either untreated or stimulated by Con A or LPS) and in mitogen-stimulated GVHR spleen cells. (B) Time course of iNOS RNA expression in GVHR spleen cells (either untreated or stimulated by Con A or LPS). Densitometric analysis of iNOS mRNA expression relative to actin is represented below the blot.