Macrophage activation / B7

[mdp96tab at shef.ac.uk]

Hello all,
I'm trying to get some B7.2 RNA for and was hoping to do RT-PCR on 
some activated macrophage cells. I'm using the human cell line U937 
and was planning on activating with LPS or PMA. My question is this... 
does anyone have any experience of activating this cell line and any 
knowledge of B7 expression during activation ?  Any advice, hints/tips 
would be greatly appreciated.

Cheers,

Tom