You can try:

THP-1 

U937

They are only monocytic, not exactly macrophages in their undffierentiated state. But their differentiation has been extensively documented in the literature. 

http://www.nature.com/nature/journal/v306/n5943/abs/306597a0.html

http://www.nature.com/nature/journal/v512/n7515/fig_tab/nature13684_SF4.html

http://www.atcc.org/products/all/TIB-202.aspx

Both are suspension cells. 

Thank you very much for your answer.

Best regards

If you want macrophages, treating THP-1 with PMA 48H prior to the measurement is also good prior to the analysis. Good luck!

I agree. Optimized THP-1 differentiation can be achieved with very low dose PMA.

Please see this methods paper.

http://www.ncbi.nlm.nih.gov/pubmed/17334670