Zinc
Sempertegui, F., et al. "Effects of short-term zinc supplementation on cellular immunity, respiratory symptoms, and growth of malnourished Equadorian children." Eur J Clin Nutr 1996. 50(1): 42-46.

Watson R.R. "Immunological enhancement by fat-soluble vitamins, minerals, and trace metals: a factor in cancer prevention." Cancer Detect Prev 1986. 9(1-2): 67-77.