Macrophages are a heterogenous population of cells that adopt specific phenotypes in response to signals from their dynamic microenvironment. Apart from being key players in innate immunity and in the maintenance of tissue homeostasis, macrophages are also important drivers of low-grade inflammation, which is associated with different chronic conditions including stress and cancer. The activation of macrophages during chronic stress and cancer results in their multifaceted pathogenic roles. Macrophages residing in the tumor microenvironment are commonly known as tumor-associated macrophages and favor or inhibit tumor growth depending on the microenvironmental cues and their activation state. Activated macrophages display a continuum of properties rather than a distinct proinflammatory or anti-inflammatory dichotomy. Emerging evidence suggests that prolonged tissue residency restricts the plasticity of macrophages, while recruited monocytes are more plastic and their differentiation into tumor-associated macrophages during stress can result in a dual imprinting from both the existing stress-induced inflammation and the tumor microenvironment. In addition, the immunomodulation of the tumor microenvironment and reprogramming of tumor-associated macrophages toward the anti-tumor phenotypes have emerged as promising therapeutic approaches. In this review, we will focus on how the persistent inflammatory state underlying chronic stress affects macrophages as well as the macrophages’ contribution to various aspects of tumor growth and progression, highlighting a therapeutic potential of modulation of the macrophage-mediated immunosuppressive tumor microenvironment.

Psychological stress is a significant contributor to various chronic diseases and affects multiple physiological processes including erythropoiesis. This study aimed to examine the tissue-specific contributions of macrophages and extracellular ATP, as a signal of disturbed tissue homeostasis, to erythropoiesis under conditions of repeated psychological stress. Adult male BALB/c mice were subjected to 2 h daily restraint stress for seven consecutive days. Clodronate-liposomes were used to deplete resident macrophages from the bone marrow and spleen two days prior to the first restraint procedure, as well as newly recruited macrophages, every third day for the duration of the experiment. Repeated stress induced a considerable increase in the number of erythroid progenitor cells as well as in the percentage of CD71+/Ter119+ and CD71−/Ter119+ cells in the bone marrow and spleen. Macrophage depletion completely abolished the stimulative effect of repeated stress on immature erythroid cells, and prevented stress-induced increases in ATP levels, P2X7 receptor (P2X7R) expression, and ectonucleotidase CD39 activity and expression in the bone marrow and spleen. The obtained results demonstrate the stimulative effects of repeated stress on erythroid cells, extracellular ATP levels, P2X7R expression, CD39 activity and expression within the bone marrow and spleen, as well as the essential role of macrophages in stress-induced changes.

Chronic stress is increasingly recognized as a major contributor to systemic disease. Prolonged or repeated activation of the hypothalamic–pituitary–adrenal (HPA) axis and sympathoadrenal systems may contribute to glucocorticoid receptor resistance and chronic low-grade inflammation, although stress-related responses vary depending on stressor characteristics, population, age, sex, health status, and study design. Elevated levels of pro-inflammatory cytokines (IL-6, IL-1β, TNF-α), oxidative stress, and NF-κB activation contribute to immune dysfunction, neuroinflammation, metabolic disturbances, reproductive and endocrine imbalance, as well as structural and functional alterations in stress-sensitive brain regions. Prolonged exposure to stress may contribute to the development of neuropsychiatric, cardiovascular, metabolic, neurodegenerative, and malignant diseases, highlighting the need for effective strategies to mitigate the detrimental consequences of chronic stress. Given the limitations and adverse effects associated with conventional pharmacological approaches, increasing attention has been directed toward natural bioactive compounds. Terpenes represent a diverse class of phytochemicals with reported anti-inflammatory, antioxidant, and neuromodulatory properties. Terpenes such as limonene and β-caryophyllene, as well as terpenoids such as linalool, may modulate NF-κB, MAPK, and Nrf2 signaling pathways and interact with the endocannabinoid system, thereby attenuating neuroinflammation, oxidative stress, and stress-induced immune dysregulation. This review summarizes current evidence regarding the mechanisms linking chronic stress, HPA axis dysfunction, and systemic disease, with particular emphasis on endocrine, immune, and nervous system alterations. In addition, it critically evaluates the mechanistic and translational potential of terpenes as possible indirect neuroimmune and redox modulators of stress-related pathophysiology.