Psychosocial stressors-life events that challenge social support and relationships-represent powerful risk factors for human disease; included amongst these events are relocation, isolation and displacement. To evaluate the impact of a controlled psychosocial stressor on physiology and underlying molecular pathways, we longitudinally studied the influence of a 28-day period of quarantine on biomarkers of immune signalling, microbial translocation, glycaemic health and blood transcriptome in the wild-born vervet monkey. This event caused a coordinated, mostly transient, reduction of circulating levels of nine immune signalling molecules. These were paralleled by a massive dysregulation of blood transcriptome, including genes implicated in chronic pathologies and immune functions. Immune and inflammatory functions were enriched among the genes downregulated in response to stress. An upregulation of genes involved in blood coagulation, platelet activation was characteristic of the rapid response to stress induction. Stress also decreased neutrophils and increased CD4 + T cell proportions in blood. This model of psychosocial stress, characterised by an immune dysregulation at the transcriptomic, molecular and cellular levels, creates opportunities to uncover the underlying mechanisms of stress-related diseases with an immune component, including cardiovascular diseases and susceptibility to infections. Psychosocial stress is a key risk factor for numerous chronic diseases, particularly cardiovascular (e.g., hypertension and atherosclerosis), metabolic (e.g., diabetes), and neuro-psychiatric morbidity (e.g., depression and anxiety, substance use disorders, neurodegenerative disease and psychosis) 1-8. Stress responses constitute an adaptive strategy for maintaining bodily homeostasis in physically or psychologically challenging situations and are, in part, orchestrated by the hypothalamus-pituitary-adrenal (HPA) axis and controlled by its end products, glucocorticoids, through a negative feedback loop. However, prolonged exposure to stress, chronic activation of the HPA, and continuous secretion of glucocorticoids exert maladaptive effects and lead to the wide range of health complications mentioned above. Cortisol is regarded as a major mediator of a range of stress responses affecting many body systems, including the suppression of HPA activity, regulation of immune functions, glucose metabolism, and gene expression across different organ systems and, if chronically elevated, is a key driver of stress-related pathologies. Cortisol is commonly used physiological indicator of an individual's response to stress; 9,10 notably, however, this relationship is moderated by multiple biological and environmental variables (including-but not limited to