Changes in mononuclear phagocyte microtubules after endotoxin stimulation. I. Changes in microtubule stability

Microtubules are in a dynamic equilibrium of polymerization and depolymerization. In monocytes and macrophages, microtubules bind endotoxin and partly regulate inflammatory events such as cytokine production. To characterize the morphologic differences between alveolar macrophage and blood monocyte microtubules after LPS stimulation, cells were examined by immunofluorescent microscopy and laser confocal microscopy. Fresh monocytes contained an average of 26 microtubules per cell which significantly increased to 31 microtubules per cell following a 30-min exposure to LPS (P < 0.001). Using a nocodazole-based assay of microtubule dynamic instability, the half-life of fresh unstimulated human monocyte microtubules was approximately 18 s and extended to 26 s following a 30-min exposure to LPS. In vitro maturation of monocytes for 18 h increased microtubule stability but not number. Compared to monocytes, alveolar macrophage microtubules were longer, more numerous, and much more stable. These results suggest that alveolar macrophage microtubules are more numerous and stable than blood monocyte microtubules and that LPS causes an increase in monocyte microtubule number and stability.