Zinc induces thymulin secretion from human thymic epithelial cells in vitro and augments splenocyte and thymocyte responses in vivo.

Zinc is incorporated into zinc-thymulin by the thymus and in this form is a critical hormonal regulator of cellular immunity. In the absence of serum, zinc induces human thymic epithelial cells (TEC) to secrete a factor which promotes the expansion of interleukin-2 (IL-2) receptor positive human peripheral blood lymphocytes in response to a low dose of phytohemagglutinin (PHA). This factor is removed by antithymulin antisera plus filtration and is thus presumed to be zinc-thymulin. Intraperitoneal treatment of hydrocortisone treated aged mice with zinc-thymulin (100 ng/day x 5) resulted in mild augmentation of splenocyte but not thymocyte responses in vitro to IL-1, IL-2, and natural cytokine mixture (NCM) and to PHA and concanavalin A (Con A) (average increase 40%). Like zinc-thymulin treatment, oral ingestion of zinc (72 micrograms/day x 5) resulted in augmentation of splenocyte IL responses; in contrast, it augmented thymocyte responses to all stimuli (average increase 100%). These preliminary experiments indicate that treatment with zinc may have immunotherapeutic relevance, particularly in the aged and stressed organism.