Thymic peptides and neuroendocrine-immune communication

Introduction Communication between the neuroendocrine and immune systems is crucial to host defence in both health and disease for it provides a humoral means whereby the central nervous system may fine tune the immune system and thereby bring to bear the influence of a variety of physical, emotional and environmental factors. In the past decade, several lines of communication between the two systems have been identified. These include direct autonomic innervation of lymphoid tissues and humoral factors derived from immune cells (e.g. cytokines, eicosanoids, peptides) and peripheral endocrine glands (e.g. peptides, steroids). Central to this complex interplay are the thymic hormones, a heterogeneous family of polypeptides produced by the thymic epithelium whose members include thymosin α1, thymosin β4, thymopoietin, thymulin, MB-35 and a number of less well-characterized peptides (Table 1). These peptides possess a spectrum of immunoregulatory properties. In addition, they provide the basis of a significant humoral