Legionella pneumophila-induced suppression of macrophage spreading in vitro.

Incubation of normal mouse resident peritoneal cell suspensions rich in macrophages with Legionella pneumophila whole cell vaccine or soluble preparations thereof resulted in marked inhibition of the ability of the cells to spread on glass surfaces during a 24-h period. This inhibition, however, was transient in that by day 2 to 3 after culture initiation only partial inhibition was evident, and by day 4 to 5 thereafter most of the treated macrophage cultures showed normal spreading activity. Suppression of macrophage spreading was evident not only with intact Legionella preparations and the sonic extract but also with a lipopolysaccharide-rich somatic antigen preparation and flagella. The suppressive effects of Legionella preparations on a functional activity of normal macrophages in vitro indicate that these bacteria may have a detrimental effect on an important activity of cells involved in the immune defense system.