Differential effects of virulent versus avirulent Legionella pneumophila on chemokine gene expression in murine alveolar macrophages determined by cDNA expression array technique

The cDNA expression array technique is a powerful tool to determine, at one time from many genes, specific gene messages modulated by infection. In th e present study, we identified genes modulated in response to virulent vers us avirulent Legionella pneumophila infection of the alveolar macrophage ce ll line MH-S by the cDNA expression array technique. Many macrophage genes were found to be modulated after 5 h of in vitro infection with L. pneumoph ila. In particular, it was found that the monocyte chemotactic protein 3 (M CP-3) gene expression was significantly induced by infection with virulent L. pneumophila but not with avirulent L. pneumophila. In contrast, other ch emokine genes, such as macrophage inflammatory protein (MIP) 1 alpha, were induced by both virulent and avirulent L. pneumophila. Reverse transcriptio n (RT)-PCR assay of total RNA isolated from macrophages infected with the b acteria for 5 or 24 h confirmed the differential induction of the chemokine genes by virulent versus avirulent L. pneumophila. Thus, the cDNA expressi on array technique readily revealed differential induction by L. pneumophil a infection of select chemokine genes of macrophages from more than 1,100 g enes. These results also indicate that certain chemokine genes may be selec tively induced by virulent bacteria.