THE ROLE OF GROWTH-HORMONE AND INSULIN-LIKE GROWTH-FACTORS IN THE IMMUNE-SYSTEM

Growth hormone (GH) and insulin-like growth factor I (IGF-I) can modul ate the development and function of the immune system. In this chapter , we present data on the expression of receptors for GH and IGFs and t he in vitro and in vivo effects of these proteins. We show that expres sion of GH and IGFs in the immune system opens up the possibility that these proteins are not only involved in endocrine control of the immu ne system but can also play a role as local growth and differentiation factors (cytokines). Endocrine control of GH could be direct or media ted via endocrine or autocrine/paracrine IGF-I. In addition, GH can ac t as an autocrine or paracrine factor itself. Furthermore, IGF-I in th e immune system has been shown to be regulated by cytokines, such as i nterleukin-1 and interferon-gamma, alluding to a cytokine-like functio n of IGF-I. In addition to data on the function of GH and IGF-I in the immune system, we present new findings which imply a possible functio n of IGF-II and IGF-binding proteins.