Research concerning the effects of growth hormone on the immune system has been carried out on several fronts. One area of particular interest involves the work of Dr. Vincent Giampapa. Treating patients with HGH he has found improvements in T-cell function, in antibody synthesis, and in the cell division of lymphocytes. Most significantly, there was an improvement in two cancer fighters - tumor necrosis factor alpha, and NK (natural killer) cells. Dr. Giampapa also found HGH brought about a growth in the thymus as well as improved DNA synthesis of cells in the thymus.

An explanation of the latter finding is likely connected to another result in Dr. Giampapa's work, a study involving cell division. As part of a cell's existence, it goes through a quiescent stage, where it carries on its routine functions. Then, in another stage, the cell undergoes the process of cell division, during which some rejuvenation and repair of the cell takes place. With age, the quiescent phase grows longer, meaning that the periods between cell division and repair grow farther apart. What Dr. Giampapa found was that with HGH treatment, the periods of quiescence were reduced.

"What growth hormone does is jump start the older cell," explains Dr. Giampapa,
"Growth hormone pushes the cell so it goes into the repair and reproduction stage more quickly."

On yet another front comes another striking piece of information - this from research done by David Khansari and Thomas Gustad at North Dakota State University in Fargo. They treated older mice with growth hormone and obtained a startling result: growth hormone extended the life span of these mice by a full one third. The older mice treated with growth hormone also showed an improved production of immune factors such as tumor necrosis factor, interleukin 1, and immunoglobulin G. As well, these results tend to corroborate the thesis that the T-cells in aging animals are not innately defective, that they are capable of being rejuvenated by growth hormone.

Dr. Richard Aspinall at Imperial College School of Medicine, London U.K., demonstrated that women have higher levels of new T-cells than men of the same age, which could explain women's better resistance to infection, and hence greater longevity.