ABSTRACT
Immune functions are intricately regulated by complex physical interactions between cells of the immune system and release of autocrine or paracrine factors, i.e., interleukins or cytokines. An additional regulatory level involves components of the central nervous system (CNS), endocrine system (ES), and immune system (IS), which constitute a more extensive regulatory feedback loop subserving a myriad of physiological functions [1]. Such systems are known to share common receptors and effector molecules [2,3]. Receptor activation or alteration of the levels of endogenous or exogenous ligands can alter the immune function and possibly serve to maintain homeostasis in health and disease. Neurotransmitters, neuromodulators, neurohormones, and cytokines can affect the components of the immune system indirectly by stimulating the neuroendocrine axis or sympathetic nervous system or directly by interacting with receptors on leukocytes. Immunomodulation can
therefore be achieved by directly influencing the immune system or indirectly modulating activity of the CNS or ES [4,5].
