Expression of muscarinic receptors by human macrophages

Macrophages increase in number and are highly activated in chronic obstructive pulmonary disease (COPD). Muscarinic receptor antagonists inhibit acetylcholine-stimulated release of neutrophilic chemoattractants, suggesting that acetylcholine may regulate macrophage responses. Therefore, expression and function of components of the non-neuronal cholinergic system in monocyte-macrophage cells was investigated.RNA was isolated from monocytes, monocyte-derived macrophages (MDMs), lung and alveolar macrophages from nonsmokers, smokers and COPD patients, and expression of the high-affinity choline transporter, choline acetyltransferase, vesicular acetylcholine transporter and muscarinic receptors (M1–M5) ascertained using real-time PCR. M2and M3receptor expression was confirmed using immunocytochemistry. Release of interleukin (IL)-8, IL-6 and leukotriene (LT)B4were measured by ELISA or EIA.All monocyte-macrophage cells expressed mRNA for components of the non-neuronal cholinergic system. Lung macrophages expressed significantly more M1mRNA compared with monocytes, and both lung macrophages and alveolar macrophages expressed the highest levels of M3mRNA. Expression of M2and M3protein was confirmed in MDMs and lung macrophages. Carbachol stimulated release of LTB4from lung macrophages (buffer 222.3±75.1versuscarbachol 1,118±622.4 pg·mL−1; n=15, p<0.05) but not IL-6 or IL-8. LTB4release was attenuated by the M3antagonist, 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide (4-DAMP; half maximal effective concentration 5.2±2.2 nM; n=9).Stimulation of macrophage M3receptors promotes release of LTB4, suggesting that anti-muscarinic agents may be anti-inflammatory.