Recent studies show that in exercise, skeletal muscle releases immune system chemicals that modulate the immune response, affecting autoimmune diseases.
Cytokines are immune system chemicals that regulate immune function by their ability to send signals to white blood cells. For instance, certain pro-inflammatory cytokines such as tumor necrosis factor-alpha (TNF-α) promote inflammation, and certain anti-inflammatory cytokines such as interleukin-6 (IL-6) reduce or mediate the acute phase immune reaction. Specific cytokines modulate the immune response in different ways.
Some cytokines can cause the immune response to persist while others cause it to slow down and stop. Various cytokines account for the symptoms in autoimmune disease while others contribute to periods of remission. For many years it’s been known that cytokines are primarily produced by immune system cells. In addition, recent studies show that a group of cytokines known as myokines is also produced by skeletal muscle during periods of exercise.
Myokines and Exercise
The various cytokines and exercise factors produced and released by contracting skeletal muscle during exercise are referred to as myokines. These, to date, include IL-6, IL-8 and IL-15. These myokines have various actions. For instance IL-6 promotes the breakdown of lipids, reduces lipid levels, suppresses tumor necrosis factor (TNF) production and stimulates cortisol production.
Type of Exercise
For many years, the benefits of moderate exercise on immune function have been demonstrated. Mild to moderate exercise is well known to improve symptoms and promote general health in patients with autoimmune disorders. Up to the last twenty years, the reasons for this improvement have been unclear. With the discovery of myokines, researchers have found a scientific basis for the physiologic changes related to mild exercise such as yoga and tai chi.
However, severe, strenuous exercise, such as long-distance running, can act as a stressor to the immune system. In studies of the cardiovascular, endocrine and immune responses related to acute high-intensity aerobic exercise, exercise-induced stress may be considered a type of stressful coping. The cardiorespiratory responses of both physiological and mental stress include increases in heart rate, cardiac output, systolic blood pressure, skeletal muscle vasodilation and oxygen consumption. Nervous system and endocrine changes include increases in catecholamines as well as elevations in cortisol under high but relatively low sympathetic activation.
Immune system responses to strenuous exercise include increases in natural killer (NK) cell number and cytotoxicity and suppressor/cytotoxic lymphocytes as well as decreased proliferative response to antigenic triggers. Task and recovery periods for both acute psychological stress or severe exercise show that immune status is negatively impacted during recovery.
In addition, chronic life stressors influence acute cardiovascular, endocrine and immune responses to acute stressors. Furthermore, both chronic stress and unusually heavy chronic exercise can negatively impact immune status. Given impaired immune status following chronic stress and interactive effects of acute and chronic stressors (e.g. blunted acute NK responses to acute stressors), these factors may have negative effects in persons with autoimmune disease. Further studies are needed to show how myokine production is affected by exercise severity.
Resources:
Perna FM, Schneiderman N, LaPerriere A, Psychological stress, exercise and immunity Int J Sports Med, 1997 Mar;18 Suppl 1:S78-83.
Pedersen BK, Akerstrom TC, Nielsen AR, and Fischer CP, Role of myokines in exercise and metabolism, Journal of Applied Physiology, Mar 2007.
