Nitric Oxide is a radical hormone/neurotransmitter, which means it has an unpaired electron. Antioxidants are reducing agents, so I would not expect this compound to be an antioxidant. If it were an antioxidant, it might decrease production of NO. I could very well be wrong, but that is what chemical intuition tells me.

Edit: If you do run that assay, please post the results (unless they are classified, I guess). And to actually attempt to answer your question, I would say that an antioxidant may have indirect effects on the immune system, but the immune system is pretty much just regulated by proteins.

You wont know if you dont try it!

It is true what Cory sad about antioxidant capacity of compound and NO (some of in vitro assay are even based on NO generation)!

Also second statement is very much true! The effect of compound/s might be on the protein level (enhanced enzyme production) which is common for substances that act as immuno modulators....

Again my suggestion is to try it and see what happens (and let us know if you can)!

Oligomeric procyanidins, catechin oligomers, present in grape seed extracts and wine, elicited dose-dependent endothelium-dependent relaxation in rabbit aortic rings, which is owing to NO production; these oligomeric flavanol molecules also possess anti-inflammatory properties. They possess anti-inflammatory properties that may modify the progression of atherosclerosis They may also have beneficial effects upon blood vessels.

http://pubs.acs.org/subscribe/archive/ci/30/i09/html/kappagoda.html

(-)-Epicatechin, a flavanol present in tea, and a constituent of dark chocolate improves endothelial function (via NO production); it is an antioxidant, and also has antiinflammatory effects. Fisher ND, Hughes M, Gerhard-Herman M, Hollenberg NK. Flavanol-rich cocoa induces nitric-oxide-dependent vasodilation in healthy humans. J Hypertens 21: 2281–2286, 2003 

This makes sense. In an attempt to redeem myself, I have analyzed the data, but this is all I came up with... Maybe flavonoids potentiate the heme and NADP reductions that must take place between NOS reactions.

It is interesting that aortic rings that were exposed to polymeric flavonoids prior to the experimental acute exposure display less NOS activity than the rings that were incubated with the flavonoids. This fits with the observation that over-supplementation with antioxidants is potentially harmful rather than helpful.

Dear all,

thank you very much for your kind and valuable suggestions. I will surely let you know the results as soon as I have done with the experiment.