Apoptosis - how to rduce the the background staining for annexin V - (Jul/15/2005 )

How to rduce the the background staining 'for annexin V staining assay

i have never seen any background in my annexin-V/PI staining...
do you use the good buffer (Hepes 10mM pH7.4, NaCl 140mM and CaCl2 2.5mM) and the appropriate dilution of Annexin V? Do you incubate the cells at RT for 20minutes and analyze directly by FACS?

Seb_