Expression of TLR co-receptors in the epithelial cells also may play a role in epithelial TLR responsiveness. Hyporesponsiveness to LPS in colonic epithelial cell lines (Caco-2, T84, SW837, and in the basal state is associated with low or absent expression of the TLR4 coreceptor MD-2 (88, 191) and priming of cultured colonocytes (HT-29) with IFN-γ or TNF-α enabled LPS responsiveness in a mechanism that involved increased MD-2 expression (192) . Recently, we also have demonstrated a transient increase in the expression of the LPS co-receptor CD14 in enterocytes after exposure to LPS (193) . In the pulmonary system, absent expression of the TLR2 coreceptor CD36 has been implicated in the hyporesponsiveness of bronchial epithelial cell to Gram-positive bacteria (194) .