Hi Quirijn

I took this text from a review that I recommend you. It's about macrophages but it helps to understand the effect of priming cells.

"In tissues, macrophages are exposed to metabolic, homeostatic and immunoregulatory signals of local or systemic origin that influence their basal functions and responses to danger signals. Signal-transduction pathways regulated by extracellular signals are coupled to distinct sets of broadly expressed stimulus-regulated transcription factors whose ability to elicit gene-expression changes is influenced by the accessibility of their binding sites in the macrophage genome. In turn, accessibility of macrophage-specific transcriptional regulatory elements (enhancers and promoters) is specified by transcription factors that determine the macrophage lineage or impose their tissue-specific properties. Here we review recent findings that advance the understanding of mechanisms underlying priming and signal-dependent activation of macrophages and discuss the effect of genetic variation on these processes."

http://www.nature.com/ni/journal/v17/n1/full/ni.3306.html

If you're just doing a proof-of-concept experiment, then why not pre-treat your sample with the drug before adding LPS?  It would give you the clearest data.

Later on, if you get promising data from the above experiment, you can try treating inflamed cells with your drug to see if that reduces cytokine secretion over time.

Thanks for the answers, it makes sense and it was, in fact a proof-of-concept study. :)