Antibodies and Immunoglobulins

• Antibodies are made by B cells, including IgG, IgA, IgM, IgE, and IgD (GAMED).
• SIgA protects mucosal surfaces by preventing pathogen adhesion, neutralizing viruses, and removing immune complexes.
• SIgA is a double antibody moved across mucosal surfaces by a transporter (pIgR).
• Exercise affects SIgA levels differently, depending on intensity, duration, and measurement methods.
• Moderate exercise reduces saliva flow due to nervous system control.
• Hard training over time lowers SIgA levels, increasing the risk of upper respiratory tract infections (URTI).

Ig Classes

• IgG is the most common antibody, mostly found in blood and tissue liquid.
• IgA is the major secretory antibody, mostly found in saliva, tears, and breast milk.
• IgM is a natural antibody found in serum without prior contact with an antigen.
• IgE is involved in allergic reactions.
• IgD consists of antimicrobials and inflammatory proteins.

Antimicrobial Proteins in Saliva

• α-amylase, from acinar cells, breaks down starch into maltose and inhibits bacterial growth.
• Lysozyme, from acinar cells, breaks down bacterial cell walls to destroy bacteria.
• Lactoferrin, from macrophages, prevents bacterial growth and combats viruses.

Saliva SIgA

• Saliva SIgA consists of two IgA molecules connected tail-to-tail by a J chain.
• The J chain protects IgA from being broken down by enzymes in saliva and secretions.
• The Polymeric Immunoglobulin Receptor (pIgR) is made by mucosal cells and binds to IgA, transporting it across the cell.
• Plasma cells release IgA monomers, which bind together via a J chain, then bind to pIgReceptor and are transported to the apical surface.
• pIgR is cleaved, leaving the secretory component on SIgA to protect against digestive enzymes when saliva is produced.

Salivary Glands

• The average saliva production is 1.5 liters per day.
• The average salivary IgA concentration differs among individuals, ranging from 80 to 100 mg/L.
• Infection risk increases when the concentration drops to 30-40 mg/L, often due to dehydration.
• Stress and exercise can both inhibit salivary flow.
• Moderate physical activity generally has small to no effect on salivary IgA levels.
• The main salivary glands include the parotid, submandibular, and sublingual glands.
• The parotid gland is the largest but contributes only 25% of salivary secretion, which is watery.
• The submandibular gland contributes 70% of secretion, a mix of water, mucus, and enzymes.
• The sublingual gland contributes 5% of secretion, which is watery and mucous.

Change in Concentration of SIgA

• Infections are more likely to occur when salivary IgA levels are at their lowest.
• Training intensity is associated with a reduction in SIgA levels.
• A drop in IgA increases the risk of infection.
• Reduced IgA production, transporter depletion, or cortisol effects may explain this.
• Compare SIgA levels with an individual's normal levels rather than group averages.
• Prolonged intense single bouts of exercise (over an hour) can reduce saliva flow rate and volume, decreasing salivary IgA concentration and microbial proteins.

Effects of Extreme Environments on Immune Responses to Exercise

• Exercise in harsh environments results in more stress, weakening the immune system.
• Tough conditions (heat, cold, altitude, pollution, microgravity) increase stress hormones, worsening immune function.
• Stress hormones are released from the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic-adrenal-medullary (SAM) axis.
• Heat (hyperthermia) may directly affect immune function beyond the effects of stress hormones.
• Studies suggest saunas may reduce common cold symptoms.
• Hot water treatments can boost immune cells in cancer patients.
• Raising body temperature in cancer patients can increase immune activity temporarily.
• Heating blood to 41.5°C for hours temporarily improved immune function.
• It's unclear whether saunas or hot baths prevent infections in healthy people.
• Whole-body hyperthermia can be immunostimulatory in those with compromised immune function.

Exercise in Hot Conditions

• Exercising in hotter conditions increases body temperature, heart rate, and stress hormones.
• The body burns more carbs for energy.
• Endurance performance suffers in hot conditions.
• A core temperature rise above 1°C increases stress hormones and white blood cell counts.
• A thermal clamp can be used to study how heat affects the immune system.
• Lower core temperature results in fewer white blood cells released and lower stress hormone levels.
• Heat causes immune changes by triggering stress hormones, not directly through temperature.
• Exercise in heat mostly affects lymphocytes with little impact on neutrophils, monocytes, or mucosal immunity.
• Exercising in hot conditions increases white blood cell and neutrophil counts more than in cooler conditions.
• Heat increased the number of T cells and NK cells in the blood, whereas cooler conditions keep numbers lower.

Hormones Affected in Hot Conditions

• Cortisol, adrenaline, and noradrenaline levels are significantly increased in hot environments, with smaller increases in cold environments.

Exertional Heat Stroke

• Causes of heat stroke (EHS) include environmental heat, illness affecting heat regulation, and muscle issues generating excessive heat.
• The immune system plays a small role in heat stroke cases.
• Heat stroke = damage to blood vessels and organs, leading to increased levels of cytokines.
• New research suggests the cytokine response might help with recovery.

Immune System and Heat Stroke

• Arguments supporting an immune role in heat stroke: LPS toxin levels in ultramarathon runners are similar to severe infections, corticosteroids and antibiotics improve heat tolerance in animals, and cytokines are found in people with heat stroke.
• Arguments against an immune role in heat stroke: cytokine and LPS levels vary greatly in people with heat stroke, there is no agreement on the exact LPS levels that lead to heat stroke, and high LPS levels can be found in athletes without heat illness.

Immune System and Cold Weather

• Colds are more common in winter, when it's cold and dry.
• Some studies claim cold and wet conditions increase the chance of catching a cold, while others disagree.
• Cold exposure slows down immune cells in the nose and airways, allowing viruses to multiply and turn mild infections into full-blown colds.
• Cold temperatures decrease core temperature, cause dehydration, promote nasal vasoconstriction, skin vasoconstriction, airway drying, and indoor crowding.
• Decreases in core temperature and dehydration increase HPA and SAM axis activity, decreasing immune function and increasing infection risk.
• Airway drying increases epithelial damage and permeability, increasing pathogen availability and leading to infection.
• Indoor crowding increases pathogen availability and leads to infection.

Effects of Exercise Training in Hypoxia or at High Altitude

• NK cell activity and antibody production stay the same or improve at high altitude.
• T cell function is impaired at high altitudes due to increased stress hormones like cortisol and adrenaline.
• Wound healing is slower at high altitudes.
• A weakened immune system at high altitudes might explain why people get sick more often.
• In vivo tests are better for studying immune function than lab tests.
• Mountaineers show a weaker immune response after being at high altitudes.
• High altitudes seem to impair some parts of the immune system, especially wound healing and infection-fighting abilities.
• Mountaineers at high altitudes had lower immune responses (less skin swelling and redness) compared to those at sea level, suggesting that high altitude impairs the immune system's ability to create a strong immune memory.

Immune Function in Microgravity (Space Flight)

• Astronauts experience increased stress before launch, leading to higher cortisol levels and reduced function of immune cells (neutrophils and monocytes).
• Cell-mediated immunity (response to infection) is weaker, with reduced reaction to common antigens.
• Viruses (Epstein-Barr and herpes) may reactivate due to the weakened immune system.
• Short flights show higher cortisol levels, while stress hormone levels normalize during longer flights.
• Leukocytosis post-flight causes an increase in white blood cells due to stress during re-entry.
• Post-flight, there are higher white blood cell counts, but immune cells (neutrophils and monocytes) have reduced function in fighting infections (lower phagocytosis and oxidative burst).
• Space travel affects immune function and may make astronauts more susceptible to infections.

Key Points

• High levels of stress hormones (cortisol and adrenaline) from exercise, particularly in harsh conditions, can weaken the immune system more than exercise in better conditions.
• Heat stress (body temp >39°C) causes an increase in white blood cells (leukocytes).
• Sustained exercise in the heat has a minor impact on neutrophils, NK cell function, and saliva-based immunity but decreases lymphocyte activity.
• Exercising in cold temperatures can decrease core temperature and dehydrate the body, potentially impacting immune function.