Cigarette smoke inhibits macrophage sensing of Gram-negative bacteria and lipopolysaccharide: relative roles of nicotine and oxidant stress.
OBJECTIVE
Smoking cigarettes is a major risk factor for the development of cardiovascular and respiratory disease. Moreover, smokers are more prone to infections. This has been associated with a suppression of the immune system by smoke. However, it is not clear how cigarette smoke affects the ability of immune cells to sense pathogens. Cigarette smoke contains a large number of molecules which may mediate responses on immune cells and of these, nicotine and oxidants have both been identified as inhibitory for the sensing of bacterial lipopolysaccharide (LPS). Nitric oxide synthase (NOS) and tumour necrosis factor (TNF)-alpha are both induced in macrophages on stimulation with Gram negative bacteria or LPS.


METHODS
We used murine macrophages stimulated with whole heat-killed bacteria or LPS. We measured output of NO (as nitrite) and TNFalpha, NOS protein by Western blotting and cellular oxidant stress.


RESULTS
Cigarette smoke extract suppressed the ability of murine macrophages to release NO, but not TNFalpha in response to whole bacteria. Cigarette smoke extract also inhibited nitric oxide synthase II protein expression in response to LPS. The effects of cigarette smoke extract on nitrite formation stimulated by LPS were unaffected by inhibition of nicotinic receptors with alpha-bungarotoxin (100 units ml(-1)). However, the effects of cigarette smoke extract on LPS-induced nitrite formation were mimicked by hydrogen peroxide and reversed by the anti-oxidants N-acetyl cysteine and glutathione.


CONCLUSIONS
We suggest that cigarette smoke exerts its immunosuppressive effects through an oxidant-dependent and not a nicotine-dependent mechanism.
Department of Cardiothoracic Pharmacology, Unit of Critical Care Medicine, Cardiac Medicine, Royal Brompton Hospital, National Heart and Lung Institute, London, UK.
S K
SK
McMaster
M J
MJ
Paul-Clark
M
M
Walters
M
M
Fleet
J
J
Anandarajah
S
S
Sriskandan
J A
JA
Mitchell
D000818:Animals; D015153:Blotting, Western; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D006090:Gram-Negative Bacteria / Q000378:metabolism*; D066298:In Vitro Techniques; D008070:Lipopolysaccharides / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D009538:Nicotine / Q000009:adverse effects; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism; D016877:Oxidants / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000378:metabolism; D012906:Smoke / Q000009:adverse effects*; D014026:Nicotiana / Q000009:adverse effects*; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000378:metabolism
D008070:Lipopolysaccharides; D016877:Oxidants; D011978:Receptors, Nicotinic; D012906:Smoke; D014409:Tumor Necrosis Factor-alpha; D009569:Nitric Oxide; D009538:Nicotine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II