Hi, I think it makes a difference if you freshly isolate macrophages from mice or if you work wit this monocyte/macrophage cell line RAW 264.7. Freshly isolated macrophages with Ab to mouse IFN-αβ significantly enhanced their susceptibility to Legionella infection in vitro, thus implying a role of endogenous IFN-αβ in mediating the natural resistance of macrophages to L. pneumophila infection.

http://www.jimmunol.org/content/173/2/1266.long

Best wishes

Thanks Andreas, there are many factors affecting cells susceptibility to Legionella infection, like endogenous IFN-αβ level in primary macrophage or cell line RAW 264.7. But there is still controversial opinion for RAW 264.7. 

If this is really controversal you have to test this at least by your own .... ;)

Yeah, that's what I plan to do.

I read a bit an found that expression of a dominante negative PKC-alpha resulted RAW cells which were permessive for L. intracellular replication.

I worked with these RAW cells for some time ago and I remember them as a semi-suspension culture. Cells often detach and become suspended in the culture medium (but are still viable). I also read that some groups shake the dishes to prevent adhesion. May be this explains the conflicting data you mention .. may be some groups are working with cells in suspension and other groups let them adhere. So take care if you passage these cells to get suspended and adhered cells by scraping.