Mechanisms of Chlamydophila pneumoniae-mediated GM-CSF release in human bronchial epithelial cells

Abstract

Chlamydophila pneumoniae is an important respiratory pathogen. In this study we characterized C. pneumoniae strain TW183-mediated activation of human small airway epithelial cells (SAEC) and the bronchial epithelial cell line BEAS-2B and demonstrated time-dependent secretion of granulocyte macrophage colony-stimulating factor (GM-CSF) upon stimulation. TW183 activated p38 mitogen-activated protein kinase (MAPK) in epithelial cells. Kinase inhibition by SB202190 blocked Chlamydia-mediated GM-CSF release on mRNA and protein levels. In addition, the chemical inhibitor as well as dominant-negative mutants of p38 MAPK isoforms p38alpha, beta2, and gamma inhibited C. pneumoniae-related NF-kappaB activation. In contrast, blocking of MAPK ERK, c-Jun kinase/JNK, or PI-3 Kinase showed no effect on Chlamydia-related epithelial cell GM-CSF release. Ultraviolet-inactivated pathogens as compared with viable bacteria induced a smaller GM-CSF release, suggesting that viable Chlamydiae were only partly required for a full effect. Presence of an antichlamydial outer membrane protein-A (OmpA) antibody reduced and addition of recombinant heat-shock protein 60 from C. pneumoniae (cHsp60, GroEL-1)-enhanced GM-CSF release, suggesting a role of these proteins in epithelial cell activation. Our data demonstrate that C. pneumoniae triggers an early proinflammatory signaling cascade involving p38 MAPK-dependent NF-kappaB activation, resulting in subsequent GM-CSF release. C. pneumoniae-induced epithelial cytokine liberation may contribute significantly to inflammatory airway diseases like chronic obstructive pulmonary disease (COPD) or bronchial asthma.