NO production by (A) immuno-purified human monocytes and (B) RAW264.7 murine macrophages. Cells were fed or not with HZ or sHZ, or treated with haemin added as met-haem-albumin. A portion of the cells was additionally stimulated with IFN-gamma (100 U/mL) or a stimulatory cytokine-LPS mix (MIX+LPS) containing IFN-gamma (400 U/mL), TNF-alpha (500 U/mL), IL-1beta (100 U/mL) and LPS (20 μg/mL) (final concentrations). After 24 h incubation, NO production was measured as nitrite in the cell culture supernatants and expressed as nmole/mg cell protein. Mean values ± SE (n = 2–11). The difference between untreated/unfed controls and treated/fed cells was tested for significance:*p < 0.05; **p < 0.1.