I am struggling with evaluation of cytometric data from cell lines where I am looking for marker presence/absence. I see a slight MFI shift between unstained and stained cells but the populations overlap. I have unstained controls and FMOs but I still can't tell if this is low positivity or some unspecific binding. Unfortunately, I don't have isotype controls. As this is a cell line, 100% positivity is a real possibility, so I won't see any distinct positive subset. Is there a way to tell if this is true positivity or not?

Thank you.