In recent years, it has been well documented in several studies that there is a
close relationship among three of the most important homeostatic-control axes, the
nervous, endocrine, and immunologic systems. Clinical and experimental evidence
around the world indicates that this physiological phenomenon could be explained as
neuro-immune-endocrine interactions (NIEI). The communication between those
systems maintains the homeostasis in the presence of stressing stimuli like pathogens
(virus, bacteria, fungus, and parasites). Commonly these kinds of stressors generate
inflammation processes inside and outside the tissue. Once a pathogen gets into the
body, it activates a sensor system through the activation of the innate immune cells
such as macrophages and epithelial cells. These cells release cytokines and
inflammatory mediators to the circulation such as interleukin-6 (IL-6) and Tumor
necrosis factor-alpha (TNF-α), interacting with their specific receptors in different
types of cells (local and peripheral cells). In the nervous system, principally in the
peripheral nervous system (PNS), there are cytokine receptors to these cytokines,
capable to send information from the periphery to the central nervous system (CNS),
which is the main control center of the homeostasis. The CNS integrates the
information in specific anatomical regions in the brain stem (e.g., a nucleus of the
tractus solitarius; NTS) activating hypothalamic cells, which in turn synthesize and
secrete hormones to induce more hormones secretion from the pituitary gland and
release them into the bloodstream. Some of these hormones travel to stimulate the
synthesis and release of anti-inflammatory mediators such as the glucocorticoids,
whereas other hormones produce a direct regulatory effect on the immune system
through the interaction with its receptor, suppressing or stimulating the immune cells
accordingly to the hormones concentration, receptor expression and other molecular,
cellular and micro-environmental factors involved. In this chapter, we will review some
of the principal molecular and cellular mediators involved in the homeostasis control
by the NIE system during the infection with some kind of pathogens.
Keywords: Bacterial Infections, Cytokines, Fungal Infections, Homeostasis,
Hormones, Neurotransmitters, Neuro-Immune Biology, Neuro-Endocrine System,
Parasite Infections, Viral Infections.
