Endocrine and immune adaptation in stress.

Several regulatory processes within the immune system have been clearly established. This complex autoregulation represents a self-monitoring system which protects the organism and maintains body homeostasis. There is, however, much evidence to suggest that the immune system is also under external regulation, especially by the endocrine and neural systems. These internal and neuroendocrine signals are thought to interact in both synergistic and antagonistic fashion, and are probably integrated in feedback circuits. Neuroendocrine and immune systems seem to act in parallel in many conditions, for example in their sensitivity to in vivo dexamethasone challenge. As a result of these interactions, the immune system will probably be kept in homeostatic balance, usually on a new and proper level. Animal studies suggest that there may be adrenal-dependent and adrenal-independent effects on immune function in stress situations. A significant and sustained deviation of the regulatory systems, such as increased and non-suppressible cortisol levels in endogenous depression, does not, however, induce such major changes in immune function. This elucidates the complex and counterregulatory functions of the other external adaptative systems. During diverse, stressful life events, such as bereavement and pathological grief situations, however, the interplay of these adaptative processes may be disturbed. This may lead to changes and abnormalities in immune functions and increase an organism's vulnerability to disease states.