The inflammatory reflex--introduction.

Sepsis is the third leading cause of death in the developed world. Despite recent advances in intensive care treatment and the discovery of antibiotics, sepsis remains associated with a high mortality rate. The pathogenesis of sepsis is characterized by an overwhelming systemic inflammatory response that is central to the development of lethal multiple organ failure. This volume of the Journal of Internal Medicine contains three reviews addressing novel aspects of a system we are only beginning to understand - the interactions between the immune and the nervous systems, the 'neuro-immune axis'. Tracey (Nature 2002; 420: 853) recently discovered that the nervous system, through the vagus nerve, can modulate circulating TNF-alpha levels induced by microbial invasion or tissue injury. This cholinergic anti-inflammatory pathway is mediated primarily by nicotinic acetylcholine receptors on tissue macrophages - the pathway leads to decreased production of proinflammatory cytokines. The author reports that treatment with the acetylcholine receptor agonist, nicotine, modulates this system and reduces mortality in 'established' sepsis. Watkins and Maier (J Intern Med 2005; 257: 139) illustrate that pathological pain (induced by inflammation) is not simply a strict neuronal phenomenon, but is a component of the immune response, and is modulated by peripheral immune cells and spinal cord glia cells. This may be of importance for future development of novel drugs for neuropathic pain as well as our understanding of increased risks for infections in anaesthetic skin areas. Blalock (J Immunol 1984; 132: 1067) elucidates the possibility that the immune system actually functions as the sixth sense, sensing microbes and microbial toxins that we cannot see, hear, taste, touch or smell. Activation of the sympathetic nervous system also has predominantly anti-inflammatory effects that are mediated through direct nerve to immune cell interaction or through the adrenal neuro-endocrine axis.