The roles of prolactin, growth hormone, insulin-like growth factor-I, and thyroid hormones in lymphocyte development and function: Insights from genetic models of hormone and hormone receptor deficiency

An extensive literature suggesting that PRL, GH, IGF-I, and thyroid hormone s play an important role in immunity has evolved. Because the use of one or more of these hormones as immunostimulants in humans is being considered, it is of critical importance to resolve their precise role in immunity. Thi s review addresses new experimental evidence from analysis of lymphocyte de velopment and function in mice with genetic defects in expression of these hormones or their receptors that calls into question the presumed role play ed by some of these hormones and reveals unexpected effects of others. Thes e recent findings from the mutant mouse models are integrated and placed in context of the wider literature on endocrine-immune system interactions. T he hypothesis that will be developed is that, with the exception of a role for thyroid hormones in B cell development, PRL, GH, and IGF-I are not obli gate immunoregulators. Instead, they apparently act as anabolic and stress- modulating hormones in most cells, including those of the immune system.