Psychoneuroimmunology (PNI) is a discipline that has emerged during the last four decades to investigate the link between immunity, the endocrine system, and the central and peripheral neurological systems. Neurotransmitters, hormones, and neuropeptides have been shown to influence immune cells, allowing them to connect with nervous tissue via cytokine release. Here CNS and brain, products play a critical role in balancing cellular (Th1) and humoral (Th2) immune responses. Analyzing the effects of stressors provides a good example of how this notion operates in vivo. Chronic stress has been shown to dramatically affect immune system function and change the development of numerous skin disorders, and psychological therapies have proven to be useful.
If you’ve ever felt sick when under a lot of stress, you won’t be surprised to find that your stress level affects your immune system. Psychoneuroimmunology is the study of how the immune and central neurological systems interact. Psychological stress increases your susceptibility to everything from common colds to autoimmune disease flare-ups.
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Overview of Immune System Divisions and Functions
The immune system can be divided into two main divisions: the innate immune system and the adaptive immune system. The innate immune system responds quickly to a variety of pathogens and danger signals, such as those released by dying or damaged cells. One of the most important cell types in the innate immune system is macrophages, which are present in most tissues in the body. Some macrophages are derived from monocytes present in the blood. When these cells encounter signs of infection or damage, they release specific proinflammatory cytokines, triggering an inflammatory response. These cytokines act both locally (i.e., in the area where the pathogen or injury has occurred) to promote the migration of other immune cells to the area of infection, and systemically (i.e., throughout the rest of the body). It acts to reduce fever and other physiological and behavioral symptoms.
According to RCI Registered Clinical psychologist Nidhi Singh, everything related to cognitive functioning—including how people think, decide, and judge—affects each other. So, all these three factors are affected in a way that influences each other. For example, if someone experiences stress, it impacts their immune system. Conversely, if their immune system is weak due to an unhealthy lifestyle and excessive stress, it can create negative thoughts in their brain. The body and brain are connected in such a way that handling stress, thoughts, and perceptions well can reduce susceptibility to complex psychological issues or disorders. This is how it affects people’s immune system and central nervous system.
Adaptive Immune System:
Macrophages also help eliminate pathogens and damaged cells through phagocytosis. The adaptive immune system provides a second line of defense against pathogens that cannot be eliminated by the innate immune system alone. This system is more targeted and requires time (i.e., several days) to develop and recruit cells specific for a particular pathogen.
The most important cell types of the adaptive immune system are T cells and B cells. There are many different types of T cells, each with different functions. 4,444 CD4 T cells (helper cells) help regulate the adaptive immune response, CD8 T cells (cytotoxic) help identify and kill infected cells, and CD17 T cells (regulatory cells) help regulate B cells are responsible for producing antibodies and are important warriors against pathogens circulating outside the cell.
One of the characteristics of the adaptive immune system is memory. After infection with certain pathogens, memory cells remain in the body and are able to respond more quickly to a second infection.
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What are Cytokines?
Cytokines are small proteins released by immune and non-immune cells and are responsible for communication between cells. Cytokines are usually produced briefly and locally in a self-limiting manner. However, levels can increase dramatically in disease, infection, other immune challenges (e.g., 100-fold increase in certain cytokines after endotoxin administration), or under certain circumstances (e.g., persistent infection, chronic stress). The cytokine network is extremely complex.
Cytokines are pleiotropic and act on multiple cell types with different effects depending on the type of stimulus and host. However, it is useful to distinguish between cytokines that promote inflammation (pro-inflammatory cytokines) and cytokines that reduce inflammation (anti-inflammatory cytokines). Importantly, cytokines and other biomarkers are produced by both immune and non-immune cells in response to a variety of stimuli. Therefore, interpreting the origin and function of circulating concentrations of these markers can be difficult. For example, adipocytes (adipocytes) may produce cytokines that have little to do with infection.
The Impact of Long-term Stress on the Immune System
Research shows that even short-term stress can affect your immune response. But the real danger comes from chronic stress that accumulates over time. Chronic stress weakens the immune system. Studies have linked chronic stress to the following illnesses:
Asthma:
Psychological stressors can trigger asthma attacks. When people with asthma are exposed to harmless substances that are thought to trigger an asthma attack, they are more likely to have a severe reaction. Another study showed that stressed people had stronger allergic reactions on skin allergy tests than non-stressed people.
Heart disease:
People who have had a heart attack are more likely to report stressful events in their lives, including: Stress at Work Stress at Home Major Life Changes, Financial Stress A study of men with heart disease found that those who had had a heart attack had three severe stress events. If you had a heart attack with these symptoms, you were twice as likely to die from heart disease.
Cancer:
Researchers are working to understand whether chronic stress promotes cancer growth. This allows the cancer to spread and grow. Part of how your body fights cancer is through anoikis. Anoikis kills diseased cells and prevents them from spreading. Stress hormones inhibit this process.
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The Influence of the Immune System on Brain Function
How does the brain learn about immune phenomena in the body? To date, three main pathways have been identified: neural, humoral, and cellular. In neural pathways, peripheral immune cells release proinflammatory cytokines that are recognized by afferent sensory nerves, including the vagus nerve. The vagus nerve transmits these signals to the brainstem and then to higher brain regions, allowing for the regulation of common disease responses.
In the humoral pathway, cytokines in the blood transmit signals to the brain through more porous regions of the BBB or through active transport mechanisms. The transport of various cytokines differs depending on brain region, and this variation influences the effects of specific cytokines on neuronal activity and behavior. In the most recently identified cellular pathway, activated microglia recruit monocytes from the peripheral blood to the brain parenchyma.
Notably, monocytes target specific regions of the brain, including regions associated with mood and anxiety (e.g., basal ganglia, amygdala, prefrontal cortex, hippocampus), at least in preclinical models of chronic stress.
Neuroinflammation and Immune-Brain Communication:
After detecting infection or tissue damage, immune cells produce pro-inflammatory cytokines and signal the brain to coordinate systemic responses (Dantzer & Kelley 2007). This inflammatory signal spreads throughout the brain, activating microglia and triggering a cascade of effects on neurotransmitters and neural processes. These include effects on the availability and activity of monoamines (serotonin, dopamine, norepinephrine) and glutamate, as well as neural circuits and regions related to mood and cognition (basal ganglia, ventromedial prefrontal cortex, subgenicular and dorsal prefrontal cortex).
According to clinical psychologist, Saumya Sharan, there is a connection between brain health and overall physical function. Stress, anxiety, and other mental health conditions have a direct impact on the immune system. High stress can increase the cortisol in the blood, and it directly suppresses the immune system and also leads to an increase in the inflammation biomarkers thus increasing vulnerability to infections. This phenomenon is well documented in scientific research, demonstrating increased susceptibility to various infections and diseases under high-stress conditions.
Additionally, there is a close relationship between immunity and mental states like mood, vitality, and physical activity. If their mental health is impacted by any factor, it impacts their mood, energy level, and daily life. When people feel low, they avoid activities that make them feel more energetic, healthy, and happy. They try not to indulge in anything as a result of which leads to an adverse impact on their physical. The nervous system is closely associated with other bodily functions like digestive processes too When a stressful response happens, it affects these systems which can then lead to digestive problems such as vomiting, pain, diarrhea, and decreased desire for physical activity, thus hampering the chances of getting better.
Sickness Behavior:
Resulting from these neuroimmune changes is sickness behavior, a complex syndrome that includes decreased motor activity, social withdrawal, reduced food and water intake, and increased slow-wave sleep (Dantzer & Kelley 2007). Similarities between sickness behavior and symptoms of depression were quickly noted (Yirmiya 1997), and subsequent studies showed that sick animals showed increased immobility on forced swimming and tail-hanging tests, as well as decreased mood.
Importantly, these changes are not simply due to the depletion of energy resources. Rather, they represent goal-directed behaviors aimed at maximizing recovery and protecting the host. In particular, lethargy, social avoidance, and anhedonia caused by inflammation help conserve energy that can be used to fight infections and promote wound healing (Miller & Raison 2016). These actions also help reduce the likelihood of future attacks and reduce the spread of infection.
Immune Changes in Mental Disorders
The inflammatory response, as well as the resulting changes in mood, cognition, and behavior, are thought to be a natural, adaptive reaction to injury or infection that is temporary and resolves once the pathogen is eradicated. Prolonged inflammation, such as from a chronic inflammatory illness, IFN-α treatment, or recurrent stress, can lead to clinically severe symptoms. A vast amount of observational research, summarized below, has investigated changes in inflammatory processes in people with depression and other psychiatric illnesses. Despite the absence of experimental control in the models, this study provides consistent evidence that inflammation is a likely contribution to psychiatric problems in a subset of people.
Research suggests that social, neurocognitive, and behavioral factors influence immune system processes, making psychosocial therapies effective for improving immune-related health outcomes.Immunologic activity has been linked to psychosocial elements like stress, negative emotions, and social support, rather than only pathogen exposure, physical injury, and internal physiological processes.
Chronic stress can suppress cellular and humoral immunity and increase nonspecific inflammation. However, psychosocial resilience factors like social support and connection have been shown to improve immune function and health.
Impact of Psychosocial Interventions on the Immune System
In light of these results, numerous studies have examined whether interventions that reduce stress or enhance psychological resources can improve immune system function. However, research on this topic is mixed. Some studies have found that psychosocial interventions clearly increase immunity, while others do not. , This work also had some limitations. First, existing reviews and meta-analyses do not focus on comparing the outcomes of different types of interventions, but mainly focus on only one type of intervention, such as Cognitive Behavioral Therapy (CBT), Meditation, Mind-Body Interventions Lifestyle Interventions, Mind-Body Therapy, Stress Management Interventions or Non-therapy Specific Interventions.
Therefore, certainty remains unclear. The intervention is more reliably associated with improved immunity than other interventions, which is critical for informing policy. Second, existing meta-analyses have shown that 4,444 populations with specific diseases, such as 4,444 adults with HIV, 24,30 adults with depression, 32,30 breast cancer patients, 33 or populations with other chronic diseases, is mainly limited to. Therefore, although informative, it is not discussed. An important question is whether the effectiveness of different psychosocial interventions varies depending on the medical condition and the reason the patient seeks treatment. Finally, existing meta-analyses either collapse across different markers, obscuring potential marker-specific effects, or evaluate only a small number of markers, rather than examining a variety of immune markers. This has hindered research into whether various psychosocial interventions are effective. Some are more consistently associated with immunological markers than others.
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Future research
Future PNI research could help to better understand the relationships between resilience traits and human consciousness. PNI is a rapidly growing field of study that examines the relationship between the CNS and the immune system. While some studies have raised more concerns than answers, doctors today recognize that both physical and emotional stress can have a significant impact on your immune system.
The future of PNI will most likely revolve around how this link impacts specific ailments, such as cancer and psoriasis. It could even lead researchers to long-awaited treatments for both of these diseases, among others.
References+
- Kiecolt-Glaser, Janice K. “Psychoneuroimmunology: Psychology’s Gateway to the Biomedical Future.” Perspectives on psychological science: a journal of the Association for Psychological Science vol. 4,4 (2009): 367-9. doi:10.1111/j.1745-6924.2009.01139.x
- Tausk, Francisco et al. “Psychoneuroimmunology.” Dermatologic therapy vol. 21,1 (2008): 22-31. doi:10.1111/j.1529-8019.2008.00166.x
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