Chlamydophila pneumoniae inhibits corticosteroid-induced suppression of metalloproteinase-9 and tissue inhibitor metalloproteinase-1 secretion by human peripheral blood mononuclear cells

Chlamydophila pneumoniae infection has been suggested to be associated with severe asthma characterized by persistent airway limitation, which may be related to airway remodelling. We investigated whether C. pneumoniae infection affected the secretion of metalloproteinase-9 (MMP9) and tissue inhibitor metalloproteinase-1 (TIMP1), and altered the responsiveness of inflammatory cells to corticosteroids. Human peripheral blood mononuclear cells (PBMCs) were cultured in vitro in the presence or absence of C. pneumoniae. Secretion of both MMP9 and TIMP1 was strongly suppressed by dexamethasone treatment in uninfected cells. MMP9 secretion was also significantly inhibited by dexamethasone in C. pneumoniae-infected cells, but TIMP1 secretion was not; hence the MMP9 to TIMP1 ratio decreased. Interestingly, expression of human glucocorticoid receptor beta, which is believed to confer resistance to corticosteroids, was enhanced by dexamethasone treatment in C. pneumoniae-infected PBMCs. We conclude that C. pneumoniae infection may promote airway remodelling by decreasing the ratio of MMP9 to TIMP1 secreted by inflammatory cells, and by altering cellular responsiveness to corticosteroids.