Immune System and Exercise

Body Recognition of Foreign Agents

• The body uses thumbprints (MHC - Major Histocompatibility Complex) to identify what belongs and what doesn't.
• Foreign bodies without the correct MHC are recognized as threats, prompting an immune response.

Phagocytes: The Pac-Man of the Immune System

• Phagocytes, particularly macrophages, engulf foreign bodies that do not match the body’s MHC.
• Once engulfed, enzymes within vesicles break down the foreign material into residual bodies.
• Residual bodies are processed and eliminated by the kidneys and liver.

Types of Phagocytes

1. Neutrophils
   • Act as the first responders to tissue damage or infection.
   • Arrive at the injury site within an hour to clean up.
   • They release cytokines to attract more immune cells.
2. Macrophages
   • Migrate to the site after neutrophils have initiated cleanup.
   • Responsible for serious repair and cleanup of damaged tissues.
   • Considered as the "physician" of the immune system.

Cytokines and Immune Response

• Cytokines serve as chemical messengers in the immune system, signaling the need for more immune cell support at sites of damage.
• They attract neutrophils and macrophages to sites of injury through signaling pathways.
• Increased blood flow (vasodilation) is critical for bringing immune cells to the affected area, which causes swelling.

Inflammation

• Acute Inflammation
  • Characterized by localized redness, heat, swelling, and pain; typically resolves in a few days after injury.
• Chronic Inflammation
  • A persistent state where the immune system remains activated, often leading to continuous tissue damage (e.g., COPD).
• Symptoms of Inflammation
  • Redness and heat result from vasodilation; swelling is due to increased capillary permeability allowing fluid and cells to enter tissue, causing pressure on nociceptors leading to pain.

Types of Immune Responses

• Innate Immunity
  • The body's immediate response to foreign pathogens. Includes neutrophils and macrophages.
• Acquired (Adaptive) Immunity
  • Learns and remembers pathogens for future protection, involving B cells (which tag pathogens) and T cells (which destroy infected cells).

B Cells and T Cells

• B Cells
  • Produce antibodies to tag pathogens for destruction without directly killing them.
• T Cells
  • Kill infected cells and are activated by the presence of antibodies on infected cells.
• Natural Killer Cells
  • Destroy compromised host cells and act similarly to T cells but with differing activation mechanisms.

Organ Donation and Immune Response

• Organ transplant success often requires immunosuppressants to prevent the immune system from attacking the foreign tissue, which maintains functionality while protecting from infections.
• The immune system has a memory that eventually learns to tolerate the new tissue as non-threatening.

Exercise and the Immune System

• Moderate exercise boosts immunity and decreases the risk of infections, while excessive high-intensity exercise can lead to immunosuppression due to muscle damage.
• Regular moderate intensity exercise enhances immune response and reduces susceptibility to illnesses.

Open Window Theory

• After intense exercise, the immune system is temporarily less effective (open window) as immune cells are diverted to recover damaged muscle tissue.
• The duration of this open window lasts about 3-4 hours post moderate exercise; stretches longer in cases of excessive physical stress.

Practical Recommendations

• During Illness: Exercise is generally safe for mild symptoms (above the neck). For more severe symptoms (below the neck), rest is advised.
• Exercise for Immunocompromised Individuals: Low to moderate intensity activity can be beneficial, but high intensity exercise is discouraged to prevent further immunosuppression.