Pneumolysin-induced CXCL8 production by nasopharyngeal epithelial cells is dependent on calcium flux and MAPK activation via Toll-like receptor 4

The natural niche of Streptococcus pneumoniae is the nasopharyngeal mucosa and nasopharyngeal carriage of pneumococci is widely prevalent. Pneumolysin (Ply), a pore-forming protein produced by S. pneumonia, may be important in driving the innate immune response of the nasopharynx. We studied the Ply-induced production of CXCL8 by nasopharyngeal cells and further analysed the mechanism of this induction. Detroit nasopharyngeal cells were stimulated with supernatants derived from bacterial cultures of Ply-deficient, wild-type pneumococci and recombinant Ply, and CXCL8 measured by ELISA. The role of MAP kinase family members in Ply-induced CXCL8 production was analysed using specific inhibitors, NF-κB activity was measured by immunoblot and Ply-mediated TLR4 activation analysed by a CXCL8 promotor luciferase assay. Ply significantly increased production of CXCL8 in Detroit and primary nasal cells. Flow cytometric analysis showed that Detroit cells express cell surface TLR4. CXCL8 production was dependent on changes in the intracellular Ca2+ levels and also by NF-κB via activation of TLR4, and MAP kinase signalling. Ply induces production of CXCL8 by nasopharyngeal cells using signalling mechanisms involving Ca2+ mobilisation and activation of MAPK and NF-κB via TLR4. This may be important in regulating nasopharyngeal immunity against pneumococcal colonization.