The co-localisation of DNA (DAPI, Hoechst) with histones and granular proteins (MPO/NE/etc) is generally seen as evidence for NETosis, but there are other methods (including chromatin density) that are described.

It is important that you chose a method appropriate for your sample! Some granular proteins differ between species (although NE and MPO antibodies will usually cross-react between mouse and humans), and you will most definitely find tissue trickier than cells! I would suggest you start with stimulated human neutrophils (PMA very effective and reliable in inducing NETosis here) and once you are comfortable that your IF protocol works progress from there, if that is where you are going.

Good luck!

Right now various molecular and cellular events are being tested simultaneously for confirmation of NETs formation but PAD4 inhibition, detection of citrullinated H3, extracellular appearance of various granular LL37, MPO and Neutrophil elastase  with DNA, elevated level of ds-DNA, loss of plasma membrane integrity all together are considered as NETs marker. Detection of most of them are based on IF, and elevated level of ds-DNA is being quantified by picogreen assay.

Markers on NETs would include H3Cit, NE, MPO etc. overlapping with DNA staining as described by some of us. It is currently accepted though that any neutrophil specific proteins (NE, H3Cit) would be sufficient to identify NETs.

You may want to look at how this group did it, as they first described PAD4 and H3Cit. Cheers and best of luck.

Thank you all for your responses. 

So far, circulating free-DNA from plasma is being used widely as a marker of NETosis. But it cannot differentiate the DNA from NETosis, apoptosis or necrosis. You may measure MPO-DNA or NE-DNA by ELISA. But it takes long time (3 days).