Use of cDNA microarrays to analyze responses to pneumococcal virulence factors.

BACKGROUND & OBJECTIVES The complex interactions that occur between host and pathogen during bacteraemia caused by Streptococcus pneumoniae are not well understood. Upon entering the blood stream the pneumococcus intiates responses through contact with naïve monocytes and macrophages resulting in an inflammatory response. To elucidate the role of microbial virulence factors in the host response to the pneumococcus, cDNA microarray analysis was used to identify genes in THP-1 cells, a human monocytic cell line, that are responsive to pneumococcal virulence factors. METHODS S. pneumoniae D39, a serotype 2 pneumococcus, and PLN an isogenic mutant of D39 that does not express pneumolysin were used. Gene expression profiles elicited by both wild-type and mutant were compared with that of THP-1 cells not exposed to pneumococci. Results obtained from microarray analysis were confirmed and further characterized using reverse transcriptase (RT)-PCR, real-time RT-PCR, and ELISA. RESULTS Genes in THP-1 cells that were responsive to the pneumococcus independent of the presence of the specific virulence factor, pneumolysin, were identified. THP-1 cell genes that were differentially expressed independent of pneumolysin included the ones involved in cell-to-cell signaling and antipathogen responses. Those that were responsive to pneumolysin included genes encoding adhesion molecules, chemokines, cytokine receptors, and cell cycle and apoptosis proteins. INTERPRETATION & CONCLUSION The global transcriptional response of naïve monocytes to contact with the pneumococcus was characterized and the utility of cDNA microarray analysis in elucidating the role of specific factors in host-pathogen interactions were demonstrated.