Psychoneuroimmunology - mind-brain-immune interactions : mind and body : SAMJ forum

Abstract

Psychoneuroimmunology (PNI) is the study of interactions between psychological, neuroendocrine and immune processes under basal, disease and therapeutic conditions. It expands the understanding of disease, recognising that psychological phenomena and social context can influence the aetiology and progression of and recovery from illness. While debate continues regarding the way in which intangible mental processes and identifiable physiological ones interact, there can be little argument that these psychological processes require an evolved nervous system, with certain neural networks — identified through imaging studies and neurological disease affecting the mind — related to mental and emotional functions. 1 The extension of the mind/brain relationship to include the immune system is predicated on the presence of multiple neuropeptides and their receptors in cells of the immune system, where they are produced and expressed de novo with high sequence homology to their neuroendocrine relatives, as well as structural links between lymphoid organs and noradrenergic and peptidergic nerve fibres. 2 Furthermore many immunopeptides and their receptors are produced de novo in discrete regions of the brain, most specifically the limbichypothalamic axis, where they may exert a neuromodulatory effect. 2 The functionality of the immune-brain-behavioural pathway has been well described during the acute phase or sickness response. The acute behavioural and physiological changes that regularly accompany infectious illness include, for example, fever, depression, social withdrawal, increased desire for sleep, decreased interest in food and perceptual changes. As part of the immune response to infection, interleukin-1 (IL-1) acts on IL-1 receptors in the vagus nerve and in the brain to mediate such sickness behaviours. 3