Cultivating a healthy neuro-immune network: A health psychology approach

Abstract

The field of psychoneuroimmunology (PNI) examines interactions among psychological and behavioral states, the brain, and the immune system. Research in PNI has elegantly documented effects of stress at multiple levels of the neuro-immune network, with profound implications for both physical and mental health. In this review, we consider how the neuro-immune network might be influenced by "positive" psychological and behavioral states, focusing on positive affect, eudaimonic well-being, physical activity, and sleep. There is compelling evidence that these positive states and behaviors are associated with changes in immune activity in the body, including reductions in peripheral inflammatory processes relevant for physical health. Growing evidence from animal models also suggests effects of positive states on immune cells in the brain and the blood-brain barrier, which then impact critical aspects of mood, cognition, and behavior. Tremendous advances are being made in our understanding of neuro-immune dynamics; one of the central goals of this review is to highlight recent preclinical research in this area and consider how we can leverage these findings to investigate and cultivate a healthy neuro-immune network in humans.

Keywords: blood brain barrier; eudaimonic well-being; inflammation; microglia; neuro-immune; physical activity; positive affect; sleep.

Figure

The two panels of the figure illustrate key components of the neuro-immune network in the context of stress (left panel) and in the context of positive psychological processes and behaviors (right panel). The network can be considered at three levels: 1) the peripheral immune system; 2) immune cells in the brain; and 3) signaling pathways between the peripheral immune system and the brain, including the blood brain barrier (BBB). As depicted in the left panel, stress activates the sympathetic nervous system (SNS) and the hypothalamic pituitary adrenal (HPA) axis, which release chemical messengers that influence peripheral immune organs (e.g., bone marrow) and cells (e.g., monocytes). Both acute and chronic stressors are associated with higher numbers of pro-inflammatory monocytes and elevated concentrations of pro-inflammatory cytokines in the periphery. In addition, stress activates immune cells in the brain called microglia and can disrupt the structure and function of the BBB. Together, these changes play a central role in the mental and physical health effects of stress. In contrast, the right panel of the figure depicts a “healthy” neuro-immune network, which is characterized by lower levels of inflammation in the periphery and the brain. In this context, we see decreased activation of the SNS and HPA axis, fewer pro-inflammatory monocytes and lower levels of pro-inflammatory cytokines in the periphery, microglia in their resting state, and BBB integrity. Positive psychological processes and behaviors have demonstrated effects at each level of the network, which may account for their beneficial effects on health and well-being.