The Connection Between Your Immune Response to Viral Infection and Neurological Damage

Viral infections can be either subclinical or result in diseases of varying severity, usually with characteristic clinical signs in the affected host. These infections most commonly involve the nose, throat, and upper airways, or systems including the gastrointestinal, nervous, and reproductive systems. It appears that a connection can be made between viral infection and neurological damage. Continue reading to learn more on the topic.

How Viral Infections Works

At the cellular level, the virus takes over necessary host-cell functions to replicate itself. The virus evades the host’s innate immune and inflammatory responses and natural barriers to spread. The infected cells can change, become damaged, or die. As such, this can make the host sick, with symptoms that can range from mild to severe. Still, other times, the immune system may fight off the virus and you may not experience symptoms. However, not all viral infections lead to disease.

Viral Diseases Cause an Immune Response

Viruses that can be responsible for chronic infection influence immune cells to create primarily anti-inflammatory cytokines, like interleukin-10 (IL-10) and changing growth factor-β (TGFβ), and they upregulate inhibitory receptors on effector T cells. Viral infections tend to trigger a powerful immune response that is crucial for getting rid of the infection.

In an article published in Current Opinion in Virology, it was noted that measles, for example, has a complex interaction with the immune system via direct infection of B and T lymphocytes expressing CD150. The result is transient lymphocyte depletion, which is followed by immune activation that leads to life-long immunity to reinfection.

In simple terms, when a virus enters your body, it triggers your body's immune system defenses that begin with white blood cells. These cells learn to attack and eliminate the virus or the infected cells. If your body beats the virus attack, some of your white blood cells remember the virus and become more capable of responding quicker and more effectively to future infections by the same virus. This response is referred to as immunity, which can also be produced by vaccination.

Neurological Damage: Viral Infection Can Affect Your Nervous System

While viral infections typically begin in peripheral tissues, they can invade your mammalian nervous system (NS), spread to the peripheral nervous system (PNS), and even the central nervous system (CNS) in rare instances. Most viral infections cannot invade the CNS because it’s protected by effective immune responses, along with multi-layer natural barriers. However, some viruses invade the NS efficiently. This can happen either via the bloodstream or by direct infection of the nerves that stimulate peripheral tissues. As such, the result is debilitating direct and immune-mediated pathology.

Research suggests that some viruses, like alpha herpesviruses, can efficiently enter the NS and exploit neuronal cell biology, unlike most viruses in the NS that invade opportunistically or accidentally. Furthermore, the ability of the immune system to control viral infection of the CNS largely depends on how much the virus spreads from the initial site of infection to the CNS, plus the degree of the immune response.

Can Viral Infection Cause Autoimmune Disease?

Research suggests that viral infections are triggers that can lead to autoimmunity through several mechanisms. These include molecular mimicry, epitope spreading, and bystander activation. An article published in Viruses suggests that chronic viral infections are known to sustain inflammation for longer and as a result lead to autoimmune disease. Poor immune response control can also cause adverse immune reactions that impact self-antigens of the host.

Chronic Stress, Viruses, and Brain Function

Chronic stress, especially, affects brain functioning. This kind of stress can lead to adrenal fatigue. For people with Adrenal Fatigue Syndrome (AFS), which is the non-Addison's form of adrenal dysfunction, where your body's stress response is unable to keep up with life's chronic stressors, chronic stress can cause an imbalance in the Neuroaffect circuit. It comprises the brain, microbiome, and autonomic nervous system, and an imbalance in one of these systems can lead to imbalances in crucial neurotransmitters that significantly affect the others and the rest of your body. Brain fog (difficulty concentrating or focusing), being mentally drained, and memory problems (difficulty recalling information) are some of the symptoms related to AFS.

Additionally, with high cortisol levels, your body is much weaker from an immunological standpoint, since the stress hormone influences most cells that are involved in the immune reaction, especially white blood cells. With a weakened immune system, someone with AFS is more susceptible to infections and illnesses. Supporting your body with a recovery plan and nutrition may help it to better fight off viral infections and other illnesses, speeding up recovery.

Neurological Infections

These infections include a large variety of conditions that invade and affect the nervous system. They can cause chronic, severe, and even life-threatening health issues. Common forms of neurological infections include:

• Meningitis involves inflammation of the meninges--membranes that cover the brain and spinal cord.
• Ventriculitis refers to infection of the ventricles of the brain.
• Encephalitis is an infection or inflammation of the brain.
• Meningoencephalitis refers to simultaneous infection of the meninges and the brain.
• Myelitis is an infection of the spinal cord.

Meningitis and encephalitis are viruses that sometimes can directly invade the nervous system and cause neurological damage.

Neurological Damage: Your Brain’s Response to Infection

Animal research indicates that there is a connection between your brain and your immune system. When you get an infection, your nervous system communicates with your immune system, signaling that your body is under attack. It then produces a series of behavioral and physiological changes in the body that cause unpleasant symptoms of sickness. The big question is, “How and where in the brain does this happen?”

Study's Findings

Harvard researchers set out to find the answer via animal studies that examined the brains of mice. Based on the finding published in a study in Nature, researchers revealed that a small group of neurons found near the base of the brain can trigger symptoms of sickness, such as fever and loss of appetite. These neurons are located in the hypothalamus, which is responsible for controlling critical homeostatic functions. This helps to keep your body in a state of balance and good health. Also, further findings revealed that receptors in the neurons can detect molecular signals given off by the immune system.

As such, the general idea here is that the brain can sense these immune states. The neurons are at a key area of the hypothalamus right next to the permeable blood-brain barrier. This aids in the circulation of blood to the brain. Essentially, activation of the cells of the blood-brain barrier that are in contact with the blood and with the peripheral immune system occurs. In turn, the non-neuronal cells secrete cytokines and chemokines that activate the population of neurons.

With the animal study, the researchers wanted to examine the “fever effect” in autism patients. They also wanted to find the neurons that generate fever and connect them to the neurons that impact social behavior. Researchers found that several populations of neurons are activated when an animal is sick. They activated or silenced the neurons in command in the brains of the mice and identified their function by observing what happened. Additionally, the neurons mentioned in the finding project to 12 brain areas, some of which control thirst and pain sensation, for instance. This indicates that neuron activity in certain parts of the brain could affect other sickness behaviors.

Neurological Damage: Immune Response to Viruses in the Brain Is as Damaging as The Infection

Clinicians often consider that the immune response to a virus in the brain is as damaging as the viral infection itself. The common approach to addressing viral encephalitis is with the use of immune suppression along with antiviral approaches.

Research published in PNAS suggests that death in infection with the neuroadapted Sindbis virus results from immune-mediated damage to infected neurons, not by the infection itself. Death occurs when T cells enter the central nervous system. The absence of the immune-suppressive cytokine, known as IL-10, causes an earlier onset of paralysis and increases the risk of death. Additionally, an interesting conclusion that the researchers made is that immunity to infected neurons was more crucial in survival than in the viral infection itself.

There are competing facets of the pathology of brain infection. One notable facet is the viral invasion of the brain itself causes neurological damage and pathology to neurons. In poliomyelitis, the motor neuron undergoes a series of pathologic changes resulting in paralysis and death. It was never clear that damage to motor neurons was a result of viral infection or from the subsequent immune attack.

Our Immune Responses and Not Viral Infections Cause Neurological Damage

Researchers from McMaster University have discovered that the immune system’s responses are responsible for neurological damage and not acute viral infections. Their research findings published in Nature Communications suggest that it’s not the virus itself that is responsible for the damage, but a specific population of T cells in the immune system is the culprit. Focusing on the Zika virus in laboratory testing, the researchers found that T cells specific to Zika were created to kill infected cells.

Additionally, further findings revealed that some T cells specific for Zika were not functioning like normal T cells; instead, they were eliminating lots of cells that were not infected with Zika. Specifically, NKG2D+CD8+T cells have an aggressive immune system response and are responsible for neurological damage that occurs from infections beyond the Zika virus, including septic shock and SARS-CoV-2. This response results from large amounts of inflammatory cytokine proteins created in the body.

When your body’s immune cells overreact and overproduce inflammatory cytokines, this can cause non-specific activation of your immune cells. This, in turn, leads to collateral damage which can have severe consequences if it occurs in the brain. In moderation, these proteins help your body coordinate the immune responses to fight infection or injury by communicating to immune cells where in the body to go and what to do once they arrive.

With the research findings, researchers can establish new paths and targets for ameliorating neurological diseases that are caused by viral infections.

Can Fever Cause Neurological Problems?

Under particular conditions, high fever can lead to neurologic complications, especially in susceptible individuals. Several neurologic disorders, infectious and noninfectious alike, manifest fever as a symptom. Fever can be viewed in association with neurologic disease in a few ways, including neurologic impairment caused by fever itself, fever as the only symptom of a central nervous system infection, and primary neurologic diseases with fever as a sign. Additionally, fever may result in short-term neurological and cognitive dysfunction.

The Takeaway

Viruses may cause chronic infection and influence immune cells and immune response. This response helps to eliminate the virus from the body. Additionally, a viral infection can affect your nervous system and cause neurological damage under certain circumstances.

However, your immune system may be able to control viral infection of the CNS depending on how much the virus spreads to the CNS and the level of the immune response. If you would like to learn more about boosting your immune system so your body can handle a viral infection, call us at +1 (626) 571-1234. You can learn about natural approaches to supporting your immune system.