It is best to have multiple lines of assessment- WB, IF (FLICA) and cytokine release provide corroborative evidence and more likely than not, the reviewers would expect you to have more than one assay.
I agree with Yang & Deepika. If you are using FAM FLICA then consider two parameters:
1. Change in intensity
2. Change in frequency over considered intensity.
Your caspase1-/- controls will still have some cells in FLICA+ gates. You will have to set a threshold for that background. In one of our paper, we established a 130% threshold over no caspase-1 control, which gave us more accurate and unbiased results. If you are considering imaging, then take a phase contrast image to get a gross morphology of the cell and determine some characteristics of apoptosis. This might help ruling out false positives.