Stress and chronic illness: The inflammatory pathway

Abstract

Recent studies have provided important insight into how immune system responses mediate the effects of social adversity and age on chronic illness. Simons et al.’s (2017) ITACT Ratio is a novel assessment of immune functioning that helps expand the toolkit of health psychology. Not only is this study noteworthy in showing how socioeconomic disadvantage may influence immune cell profile, but also it may prompt future work in other domains to use this new index of inflammatory dominance, the ITACT Ratio. This demonstration that social adversity gets “under the skin” through the immune system has much potential for expansion: combining ITACT with other common markers for stress and inflammation, including additional measurements for perceived stress, and expanding the investigation of the link between ITACT and chronic disease in additional populations. Results of future studies will determine if ITACT will emerge as an important new biomarker tying inflammatory dominance to chronic disease.

Keywords: Biomarker; Chronic disease; Health disparity; Immune system; Inflammation; SES; Social adversity; Women.

Figure 1.

Overview of hypothesis and methods in Simons et al. (2017). A.: Mediation hypothesis suggests the influence of social adversity and age on chronic illness is mediated by increased inflammatory load. Chronic Illness was measured by the following 8 items: heart trouble, diabetes, kidney disease, cancer, effects of stroke, circulation trouble in arms and legs, emphysema or chronic bronchitis, and cataracts. B.: Methods employed in Simons et al. (2017) used inflammatory to antiviral cell type (ITACT) ratio to evaluate immune dominance. Such a measure might be viewed as assessing the extent to which the immune system’s innate (inflammatory) program has come to dominate the acquired (largely antiviral) program Analyses using this program linked the methylated genes associated with our cell ratio measure to several biological pathways. These pathways involved processes such as wound healing, cytokine production, inflammation, and regulation of the immune system. These findings support the idea that our cell ratio measure assesses increased dominance of the inflammatory program of the immune system. Cole and his colleagues note that the immune system comprises two rather distinct programs: proinflammatory cytokine genes which combat tissue damage, bacteria, and other extracellular pathogens, and antiviral genes which produce antibodies and target intracellular pathogens such as viruses. They argue that adversity (threat or danger) leads to increased expression of the inflammatory program, coupled with decreased expression of the antiviral program, as the organism prepares for possible attack and injury. Cole (2014) labels this pattern of gene expression the conserved transcriptional response to adversity (CTRA). Support for this idea comes from studies reporting a link between various types of social adversity (loneliness, low SES, bereavement, PTSD) and the CTRA transcription pattern in blood leukocytes (Slavich & Cole, 2013; Cole, 2014). Is this a situation where ‘that’ is better due to restrictive clause?