Psychoneuroimmunology is a relatively new field that investigates interactions between behaviour and the immune system, mediated by the endocrine and nervous systems. The immune and (CNS) central nervous system,maintain extensive communication. On the one hand, the brain modulates the immune system by hardwiring sympathetic and parasympathetic nerves (autonomic nervous system) to lymphoid organs. On the other hand, neuroendocrine hormones such as corticotrophin or substance P regulate cytokine harmony. Vice versa, the immune system modulates brain activity including body temperature and sleep. Based on a functional and anatomical link, the immune and nervous systems act in a highly reciprocal manner. From fever to stress, the influence of one system on the other has evolved in an intricate manner to help sense danger and to mount an appropriate adaptive reaction. Over recent decades, reasonable evidence has emerged that these brain-to-immune interactions are highly modulated by psychological factors which influence immunity and immune system-mediated disease.