Selective impact of zinc on human circulating CD56^dim NK cells

Natural Killer (NK) cells are essential for recognizing aberrant and virus-infected cells. Adequate levels of the trace element zinc are known to be important for proper immune functionality against infections and tumor growth. So far, not many studies have analyzed the effects of zinc on NK cells. We previously observed higher levels of activated CD69⁺ NK cells in zinc-adequate compared to zinc-deficient donors. We therefore aimed to analyze the influence of zinc on the activation and functionality of NK cell in vitro.

Peripheral blood mononuclear cells were freshly isolated from young healthy donors. Serum zinc levels and Adjusted Zinc Diet Score (AZDS) were determined. NK cells, CD56^dim NK cells, and CD56^bright NK cells were analyzed ex vivo or cultivated in zinc-deficient, zinc-adequate, and zinc-supplemented media for 1 or 20 h ± specific inhibitors. CD56^dim NK cell frequencies, phenotype, and functionality were analyzed via flow cytometry, qPCR, and Western blot.

The frequencies of cytotoxic CD56^dim NK cells positively correlated with serum zinc as well as AZDS. CD69 expression was significantly increased after 20 h of zinc supplementation on CD56^dim NK cells. CD69⁺ CD56^dim NK cells showed significant higher degranulation capacity and IFNγ production. Furthermore, NFκB inhibition upregulated CD69 expression and NFKB mRNA was significantly decreased in zinc-supplemented conditions. In addition, perforin levels were sensitive to zinc deprivation.

Extracellular zinc selectively activates CD56^dim NK cells enhancing degranulation and IFNγ production. Zinc supplementation might be a useful tool for in vitro NK cell expansion protocols for future cellular therapies.