Growth hormone (GH) has been known to enhance immune responses, whether directly or through the insulin like growth factor-1, induced by GH. Studies suggest that growth hormone may promote growth of the thymus, a gland responsible for the production of important immune cells called T cells. T cells (also called T lymphocytes) are one of the major components of the adaptive immune system. Their roles include directly killing infected host cells, activating other immune cells, producing cytokines and regulating the immune response.Another study stated that GH may have stimulatory effects on the production of the cytokine such as: IL-2 and IL-6 while also enhancing the cytotoxic activity of human natural killer (NK) cells, that are lymphoid cells that mediate MHC unrestricted killing of tumors and virally-infected cells. In this same study it revealed that ageing mice demonstrated to have a deficiency in NK activity and GH administration reversed this. https://www.researchgate.net/publication/7329964_Effect_of_growth_hormone_GH_on_the_immune_systemhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC2248326/