The Immuno-Endocrine System: Hormones, Receptors and Endocrine Function of Immune Cells. The Packed-Transport Theory
Immune cells (lymphocytes, monocytes and macrophages, granulocytes and mast cells) produce numerous hormones, store and secrete them. In addition these cells have receptors for hormones and signal transduction pathways. These functions are under the control of the central nervous system (neuro-immune regulation), and there is a dynamic multi-directional interaction within the neuroimmune circuitry. Considering the high amount of immune cells, their hormone production can rival to that of the “classical” endocrine glands. However, in contrast to the endocrine glands, which are in general mono-producers, 1.) the immune cells are poly-producers, the same cell can produce different hormones at the same time and also poly-receivers, having receptors for different hormones, 2.) immune cells are mobile and can transport the hormones in a packaged form, even though they are able to synthesize and secrete the hormones locally. 3.) immune cells have the capacity to recognize the site where their hormones are needed. It is proposed that under the control of the nervous system immune cells produce hormones for general regulation, for intrasystem regulation and for remote, local regulation. Hormone production is gender dependent. Receptors are affected by hormonal imprinting during the critical developmental periods of target cells and the imprinting influences also the hormone synthesis of immune cells for life. Some hormones can be demonstrated in the nucleus of mast cells, however their function is not known. The knock-out of one hormone's gene disturbs hormone balance in immune cells. The importance of the packed-transport hypothesis is discussed.