Growth and Lactogenic Hormones and Adaptive Immunocompetence

Abstract

Adaptive immune reactions are based on lymphocyte proliferation, and are regulated by mechanisms which are involved in growth regulation of all cells in higher animals. Growth and lactogenic hormones (GLH) or type I cytokines (TICTK) are of fundamental importance for the development and function of the immune system and indeed for the entire organism. GLH/TICTK deliver the competence signal first to lymphocytes and other cells, which enable the cells to receive stromal or adherence signals that decide what the cell will do next, proliferate, differentiate, or function. This group of signals control cell growth, is delivered by cell-to-cell and cell-to-matrix signalling. Adhesion molecules, tissue bound hormones, cytokines and matrix components mediate these signals. The antigen receptor belongs to the Immunoglobulin Family of adhesion molecules. Hence the antigen signal is capable to activate specifically the immune response, it can inhibit it also. Within the immune system antigen presentation represents the adhesion signal for which cell-to-cell interaction by adhesion molecules is obligatory. Adhesion molecules are fundamental to the organization of multi-cellular organisms and the signals delivered by them serve the basis of species, organ and tissue specific recognition. This recognition system has been perfected during evolution from self-recognition to individually specific antigen recognition. This system also plays a role in the elimination of degenerated and neoplastic cells. Cell-to-cell signaling has a dominant power over other signals to commit the cell to proliferation. The mitotic cycle is then completed by cytokine signals. Cytokines are tissue hormones which are usually, but not always, secreted by the same cells that deliver the second signal. IGF-I and insulin fulfil frequently this role, but cytokines may also deliver this third signal. The nature and combination of these three groups of signals will determine the fate of each cell, which may be survival, proliferation, differentiation and function or alternately apoptosis. Hormones and neurotransmitters, that alter signal delivery, modulate further this basic pattern of animal cell growth. It is concluded that GLH/TICTK maintain immunocompetence, which enables the immune system to respond to specific antigenic and mitogenic stimuli. Competence signalling comes from either the CNS or by TICTK, which is an autologous signal by the immune system. This dual signalling secures that the immune system is capable of surviving major disasters in the personal history of the host. Indeed memory T and B ells survive autonomously, and live trough major catastrophic events, and when the disaster is over, memory cells regenerate the adaptive immune system and bring back homeostasis of immune function which is the prerequisite for healing and homeostasis of the entire organism. The hypothalamic hormone, vasopressin (VP) regulates healing and recovery from disease.