Bronchial epithelial cells release chemoattractant activity for monocytes

Lung macrophages are monocyte-derived cells that play a central and essential part in local immunity. Because the bronchial epithelial cells that line the airway can modulate their local cellular environment by releasing chemotactic factors for neutrophils, lymphocytes, and fibroblasts, we postulated that the bronchial epithelial cells might release chemotactic activity for monocytes. To test this hypothesis, bovine bronchial epithelial cells were isolated and cultured. The supernatant fluids were collected at 12, 24, 36, 48, 72, 96, and 120 h and evaluated for monocyte chemotactic activity, using a blind-well chamber technique. The supernatant fluids possessed significantly greater chemotactic activity than medium alone, with optimal migration contained in supernatant fluids harvested at 72 h (5.8 ± 2.3 vs. 39.8 ± 2.8 cells/high-power field, P<0.001). Partial characterization of the released monocyte chemotactic activity revealed that the cells released a low-molecular-weight lipid-soluble chemotactic factor after 24 h in culture, but in contrast, a high-molecular-weight protein chemokinetic factor was released after 72 h in culture. These findings suggest that bronchial epithelial cells may release chemotactic activity for, and thus may modulate the recruitment of, monocytes into bronchial passages.