negative control readings - (Jun/18/2018 )

Hi. I would like to look into the effect of a compound on treated and untreated cells. For my negative controls (comprising of untreated cells), upon staining with antibody, I get a range of 1 to 2% antigen positive cells. My doubt is, whether such a 1 to 2% reading normal as my conceptual is that negative controls should not have any reading as it did not contain the expression. Thank you.

It honestly depends on your target and your experimental conditions.  Negative controls are not always completely negative in signal but rather should represent "background" in a system that is known to either be completely missing or significantly lower than your experimental conditions.  For example, a negative control for an antibody can be siRNA mediated knockdown of the target.  You are not going to completely lose all signal as knockdown is not 100% but there should be enough of a reduction in signal to be able to identify a difference in the control non-treated.  If you know for certain that the target is completely absent, then what you are getting is background and can be used to set a limit or gate your analysis as negative results for all other samples.