Defense functions of normal human bronchial epithelial cells from explant-outgrowth co-culture with human lung fibroblasts

Airway epithelial cells fulfil several functions that are implicated in protecting the airways from exogenous insults. These defense functions range from the structural integrity of mucus and the differentiation of the epithelial cell layer to the production of inflammatory mediators.

After an explant-outgrowth culture of epithelial cells from small bronchi pure populations of primary isolated normal human bronchial epithelial cells (NHBE) were cultured with lung fibroblasts as bilayer on a 24-well HTS-Transwell filter plate. The cells were grown on a collagen type I and maintained at an air-liquid interface (ALI) by feeding basolaterally with medium. Barrier properties and morphological phenotype were compared over 42 days. The NHBE formed confluent layers, expressing functional tight junctions as measured by transepithelial electrical resistance (TER). Mucus production and cilia formation reappeared in the co-culture model dependent on the individual donors after 21 to 42 days. A key function of airway epithelial cells is the production of inflammatory mediators such as the neutrophil chemoattractant interleukin 8 (IL-8) and the cytokine IL-6, which has both pro- as well as anti-inflammatory activities. Supernatants were taken from the apical and basolateral side after 7, 14, 21, 28, 35 and 42 days of the co-culture and the cytokines IL-8 and IL-6 were measured by ELISA. The levels of IL-6 and IL-8 increased on the apical side to 5078.82±954.31pg/ml for IL-6 and up to 12.04±1.02ng/ml for IL-8. Basolaterally the levels remained unchanged.

In summary, the co-culture of NHBE and human lung fibroblasts mimics the structure of native polarized bronchiolar epithelium. Mucus production and the production of inflammatory mediators such as Il-6 and IL-8 can protect the cells from exogenous insults as it would be in the proximal airways. With this model it is hoped to understand how the upper airway mucosa reacts to noxious substances and other pathological situations.