ADP-ribosyltransferase activity of Legionella pneumophila is stimulated by the presence of macrophage lysates.

ADP-ribosyltransferases are among the most biologically active of bacterial products in eukaryotes, and act by transferring the ADP-ribosyl moiety of NAD to acceptor proteins. The detection of ADP-ribosylated Legionella proteins in ultrasonic lysates of Legionella pneumophila strain Philadelphia 1 is reported. The ADP-ribosylating reaction was not influenced by addition of guinea pig spleen-cell and lung-cell lysates, but was considerably increased in the presence of lysates of guinea pig peritoneal macrophages, which are known to be target cells for virulent Legionella. It is suggested that ADP-ribosylation may play an important role in the multiplication of this pathogenic bacterium in the tissues and cells of infected organisms.