Differential Effects of Virulent versus Avirulent Legionella pneumophila on Chemokine Gene Expression in Murine Alveolar Macrophages Determined by cDNA Expression Array Technique

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Abstract
The cDNA expression array technique is a powerful tool to determine, at one time from many genes, specific gene messages modulated by infection. In the present study, we identified genes modulated in response to virulent versus avirulent Legionella pneumophila infection of the alveolar macrophage cell line MH-S by the cDNA expression array technique. Many macrophage genes were found to be modulated after 5 h of in vitro infection withL. pneumophila. In particular, it was found that the monocyte chemotactic protein 3 (MCP-3) gene expression was significantly induced by infection with virulent L. pneumophila but not with avirulent L. pneumophila. In contrast, other chemokine genes, such as macrophage inflammatory protein (MIP) 1α, were induced by both virulent and avirulentL. pneumophila. Reverse transcription (RT)-PCR assay of total RNA isolated from macrophages infected with the bacteria for 5 or 24 h confirmed the differential induction of the chemokine genes by virulent versus avirulent L. pneumophila. Thus, the cDNA expression array technique readily revealed differential induction byL. pneumophila infection of select chemokine genes of macrophages from more than 1,100 genes. These results also indicate that certain chemokine genes may be selectively induced by virulent bacteria.