Evidence that thymosins and other biologic response modifiers can function as neuroactive immunotransmitters.

An increasing amount of data supports the hypothesis that there are bidirectional circuits between the central nervous system (CNS) and the immune system. Soluble products that appear to transmit information from the immune compartment to the CNS include thymosins, lymphokines, and certain complement proteins. Opioid peptides, adrenocorticotropic hormone (ACTH), and thyroid-stimulating hormone (TSH) are additional products of lymphocytes that may function in immunomodulatory neuroendocrine circuits. It is proposed that the term "immunotransmitter" be used to describe molecules that are produced predominantly by cells that comprise the immune system but that transmit specific signals and information to neurons and other cell types. Examples would include thymosin alpha 1 and beta 4, lymphocyte-derived ACTH, TSH, and beta-endorphin, interleukin 1, interferon as well as certain other lymphokines and cytokines. The evidence that certain thymosin peptides can serve as immunotransmitters by modulating the hypothalamic-pituitary-adrenal and gonadal axes will be discussed.