Antigenic challenge may have broad ranging effects which include not only immunological changes, but also endocrine and central neurotransmitter repercussions, and may thus elicit profound behavioral sequelae. Commensurate with the notion that bidirectional communication exists between the immune and central nervous systems it has been demonstrated that manipulations which influence central neurotransmitter or endocrine activity provoke alterations of immune functioning, and conversely immunological alterations will affect central neurotransmitter and endocrine activity. It seems, as well, that environmental stressors may provoke marked alterations of the activity of each of these systems. Indeed, in several respects the variables that influence vulnerability to stressor-provoked neurotransmitter changes, likewise affect the immunological alterations engendered by stressors. Moreover, immunological challenges will affect central neurotransmitter functioning in much the same way as stressors provoke such effects. It is thought that immune derived products (including cytokines as well as peptide hormones) may act directly or indirectly to moderate neurotransmitter functioning, and centrally derived neurotransmitters and hormones may affeet receptors present on lymphocytes. In accordance with earlier suggestions, it is maintained that the immune system may be acting as a sensory organ informing the brain of the presence of antigenic challenges, and the brain may interpret such challenge as a stressor, hence leading to behavioral alterations.
Reviews in the Neurosciences
Carleton University

Anisman, H, Zalcman, S., & Zacharko, R.M. (1993). The Impact of Stressors on Immune and Central Neurotransmitter Activity: Bidirectional Communication. Reviews in the Neurosciences, 4(2), 147–180. doi:10.1515/REVNEURO.1993.4.2.147