The field of neuroimmunology investigates how the immune and neurological systems interact with each other. It was a common belief that the brain is an “immune privileged organ” as it is not affected by any immunological responses or inflammation. However, in recent decades, neuroimmunology has become a very active research area. Seeking the interconnections of these 2 systems during homeostasis, development, and injury response is the primary goal of neuroimmunologists.
The immune system protects the human body from outside invaders. Defenses work in multiple steps, firstly, it locates the tissue that is inflamed, injured, or infected, causing pain, swelling, or possible changes in blood flow. The immune system activates cells – leucocytes, macrophages, and acute-phase proteins that travel to the destination to kill and remove the pathogens.
Role of the brain in body defenses
Immune system and injured tissue signals are interpreted by brain cells. According to research, the brain has a variety of local immunological and inflammatory responses. Additionally, it controls the immune system, particularly the acute-phase response. The hypothalamus controls how we react to illness, for instance, how we feel and how much we eat and sleep when encountering a fever.
Sensory nerves and circulating chemicals convey signals from the injured tissue to the brain. Neural signals seem to be via c-fibers, which communicate pain, and via the vagus nerve from the liver- a significant site for the production of acute phase proteins.
Cytokines as defense molecules
Cytokines are usually produced in the body at very low levels but are produced quickly when the body detects the injury. They include interferons, interleukins, tumor necrosis factors, and chemokines. The majority of those molecules are produced within the damaged tissues and act on the cell within the range, some of the molecules enter the bloodstream to send signals to organs including the brain.
Bacterial and viral products, cell injury, or dangers to cell survival like poisons or low oxygen levels are the causes of cytokine production. The brain, which may switch cytokines on or off by sending neural signals to the tissues or hormones, is another crucial regulator of cytokine production.
Stress and the immune system
Stress can weaken one's immune system and lead to illness. By triggering the HPA axis, stress can have an immediate impact on the brain. In addition, stress can affect the immune system and how susceptible we are to illness. However, this relies on the sort of stress and how we react; for example, too much work or significant tragedies might hinder people's defense mechanisms. The activation of the hypothalamic-pituitary-adrenal axis is one of the important characteristics. The increased synthesis of a protein known as a corticotropin-releasing factor (CRF) in the hypothalamus is one of the primary reactions to stress in the brain. CRF goes from the hypothalamus to the pituitary gland to release another hormone, the adrenocorticotropin-releasing factor (ACTH). The hormones ACTH then move via the bloodstream to the adrenal gland, where they trigger the release of steroid hormones, some of the most potent inhibitors of inflammation and immunological response.