I want to know by FACS if a population of cells express several cytokines in basal conditions (no activation) within a given tissue. I directly get those cells ex-vivo from human tissue samples, so I fear I may not to be able to detect the cytokine because no inhibition of cytokine secretion can be applied to a human tissue sample, obviously. Can anyone suggest a protocol for intracellular cytokine staining on ex-vivo cells? Is it necessary to treat/culture ex-vivo cells with brefeldin A prior staining, or can a regular intracelular staining with PFA/saponin be made directly after cell isolation?