asked, "more info on Quercetin/Niacin interactions?"
Not for the whole immunity system. Though (Quercetin/HCQ) which raises your alkaline phosphatase. Which induces immunity response thereby cleans out your system.
Another example: alkaline phosphatase reporter gene allowing NF-κB-induced transcriptional activation Nuclear factor kappa-light-chain-enhancer of activated B cells or NF-kB is the pathway for Niacin. Example with embryonic alkaline phosphatase reporter gene https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5386139/