Differential regulation of human blood monocyte and alveolar macrophage inflammatory cytokine production by nitric oxide.

BACKGROUND: Nitric oxide (NO) has been associated with airway inflammation in asthma. Our previous work suggests that NO functions in an anti-inflammatory capacity through downregulation of stimulated cytokine secretion by normal human alveolar macrophages. Functional differences between alveolar macrophages and blood monocytes are thought to be related to maturation.
OBJECTIVE: The purpose of this study was to determine the effect of NO on stimulated cytokine production by monocytes from asthmatics and normal healthy controls.
METHODS: Monocytes and alveolar macrophages were obtained from normal volunteers (n = 13) and asthmatics with atopy (n = 7). Monocyte and alveolar macrophage cultures were stimulated with 0.5 microgram/mL lipopolysaccharide +/- 1.0 mM DETA NONOate (releases NO in culture with t1/2 = 20 hours at 37 degrees C) and incubated for 24 hours. Cell-free supernatants were collected and assayed by ELISA for tumor necrosis factor-alpha (TNF) and granulocyte macrophage colony stimulating factor (GM-CSF).
RESULTS: Nitric oxide did not inhibit TNF production in monocytes of asthmatics and normals (mean +/- SEM % TNF stimulation = 19.6 +/- 9.7). Similar to previous results, NO did inhibit alveolar macrophages (% TNF suppression = 60.6 +/- 4.4). To determine whether this differential effect of NO on the two cell populations was related to maturation, monocytes were matured by culture for 7 days. The in vitro matured monocytes demonstrated 51.7 +/- 7.9% suppression of TNF. For each cell population, the responses of the asthmatics and healthy controls were not different. The differential effect is not cytokine specific since similar results were obtained with GM-CSF.
CONCLUSION: These results demonstrate a differential effect of NO on monocyte and alveolar macrophages cytokine regulation and this effect may be related to the state of maturation.