TLR4 and adenocarcinoma: Studies using the A549 adenocarcinoma cell line as a model of human alveolar type II epithelial cells have demonstrated surface and cytosolic expression of TLR4 and CD14 [19] yet in the absence of serum in the cell culture medium, A549 cells are unresponsive, suggesting an obligate need for exogenous soluble CD14 in order to elicit a TLR4 response [20].