Negative Regulatory Molecules in the Neuroendocrine and Immune Systems: Suppressin as an Example

The early foundations of both neuroendocrinology and immunology were established by studies that linked the production, secretion, and action of circulating factors to the physiological state of an organism. These studies ultimately identified the cells of the neuroendocrine and immune systems as a rich source of such homeostatic regulatory molecules, and currently they are referred to as neuroendocrine hormones, peptides, and cytokines. More recently, two additional concepts have been added to this model. The first was that immune cells produce neuroendocrine hormones and peptides and that neuroendocrine cells produce cytokines. The second was the notion that both positive and negative factors control a variety of physiological processes. Recently, we have identified a new polypeptide negative regulator of cell proliferation that we have named suppressin (SPN). This negative regulatory molecule is also produced by both neuroendocrine and immune cells. The objective of this article is to provide an example of the biochemical, cellular, and molecular approaches used to characterize SPN and that could be used to characterize similar molecules from neuroendocrine and immune sources.