Ectopic pituitary transplants restore immunocompetence in Ames dwarf mice.

This work was undertaken to study the effects of prolactin on immune function in Ames dwarf mice. For that purpose, adult Ames dwarf mice were implanted with pituitaries from normal mice under the kidney capsule. Ectopic pituitary transplants produced the expected increase in plasma prolactin levels in male and female dwarf mice as compared to sham-operated dwarf or untreated normal mice. Body weight was significantly increased in pituitary-grafted dwarf mice of both sexes, but did not reach the values found in normal (non-dwarf) animals. Pituitary transplants induced an increase in thymus weight and in the number of lymphocytes in the thymus in dwarf mice of both sexes as compared to sham-operated dwarf controls. The weight of the thymus in grafted dwarf mice remained below values found in normal mice, while the number of thymic lymphocytes became indistinguishable from those recorded in normal mice. Effects of pituitary transplants on the spleen were similar to those described for the thymus; however, neither the weight nor the lymphocyte number in pituitary-grafted dwarfs reached the values found in normal animals. Natural killer activity of spleen lymphocytes from pituitary-grafted male and female dwarf mice was greatly enhanced as compared to lymphocytes from sham-operated dwarfs. This effect was greater in males than in females. The number of white blood cells in pituitary-grafted male dwarf mice was increased and indistinguishable from the values found in normal males. Surprisingly, this effect was absent in the females. These findings suggest that hormones secreted by the transplants, most likely prolactin and growth hormone, can enhance the immune response. This action may be mediated by direct action of prolactin and/or growth hormone on immune cells or by indirect effects.