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Overview of Innate Immunity

This series focuses on the immune system, specifically innate immunity. Previous topics covered include invertebrate immunity, first line defenses (barriers), and second line defenses (cells and chemicals). This video completes the discussion on second line defenses: inflammation and fever.

Inflammation

Definition

  • Inflammation is a localized immune response to tissue injury.

Purpose

  • It is a beneficial response designed to limit pathogen spread, destroy pathogens, and initiate tissue repair.

Benefits of Inflammation

  • Limits pathogen spread: Inflammation acts as a physical barrier to contain pathogens.

  • Promotes immune cell migration: Increased blood flow allows more immune cells to reach the site of damage, enhancing the immune response.

  • Aids in debris removal: Helps clear out dead cells and particulate matter from the injury site.

  • Increases metabolism and ATP production: Higher blood flow raises local metabolic rates, facilitating quicker healing.

Common Inflammatory Disorders

Conditions characterized by inflammation typically end with the suffix: "-itis". Examples include:

  • Dermatitis: Inflammation of the skin, often due to irritants or allergens.

  • Colitis: Inflammation of the colon, which can cause symptoms like abdominal pain and diarrhea.

  • Mastitis: Inflammation of breast tissue, often seen in breastfeeding women.

  • Arthritis: Inflammation of the joints, causing pain and swelling.

  • Gingivitis: Inflammation of the gums, often due to poor oral hygiene.

Chronic Inflammation

  • Chronic inflammation can lead to serious health problems such as:

    • Crohn's disease and ulcerative colitis: These can cause severe gastrointestinal issues and discomfort.

    • Chronic gingivitis: Can lead to tooth decay and periodontal disease if untreated.

    • Chronic arthritis: May result in joint deformity and reduced mobility.

  • Medical intervention may be necessary to manage chronic inflammation effectively.

Cardinal Signs of Inflammation

  • Erythema: Redness due to hyperemia from increased blood flow.

  • Edema: Swelling due to the accumulation of fluid in tissues.

  • Heat: Increased blood flow results in warmth at the injured site.

  • Pain: Caused by tissue damage and the release of pain-inducing chemicals like bradykinin and prostaglandins.

  • Loss of Function: This can occur if inflammation persists without proper healing.

Mechanism of Inflammation

  1. Initiation: Triggered by tissue damage (e.g., entry of splinters, burns).

  2. Chemical Release: Damaged cells release cytokines and chemokines that activate mast cells and macrophages.

  3. Mast Cell Activation: Mast cells release histamine, leading to blood vessel dilation and increased permeability.

  4. Macrophage Activation: Macrophages secrete further cytokines, increasing blood flow and attracting more immune cells to the site.

  5. Immune Response: Increased blood flow allows fluid, immune cells, and proteins like complement to exit the bloodstream.

  6. Phagocytosis: Phagocytic cells digests pathogens and debris, potentially leading to pus formation if cellular debris accumulates.

Fever

Definition

  • Fever is an abnormal elevation of body temperature, typically following pathogen exposure.

Function

  • Generally, fever is a beneficial response; it can inhibit the reproduction of pathogens, boost interferon activity, and enhance tissue repair.

Mechanism of Fever

  • Induced by macrophages communicating with the hypothalamus, raising the body's temperature set point.

  • The body's response may include shivering to achieve the new temperature set point.

  • Defervescence: When body temperature returns to normal, sweating assists in cooling down.

Risks of High Fever

  • Low-grade fevers (98.6°F to 102°F) are generally manageable and a normal immune response.

  • High fevers (103°F and above) can lead to severe complications like nervous tissue damage, seizures, coma, or potentially death depending on the underlying cause and duration.

Adaptive Immunity

  • Future discussions will cover adaptive immunity receptors and defenses, concluding with immune system disruptions.

Pathogens Evasion of Innate Immunity

  • Some pathogens have developed mechanisms to evade innate immune responses:

    • Streptococcus pneumoniae: Evades phagocytosis by producing a capsule that inhibits recognition by immune cells.

    • Mycobacterium tuberculosis: Survives within macrophages by resisting lysosomal enzymes and exploiting them as host cells.

This concludes our comprehensive overview of innate immunity, detailing the processes of inflammation and fever as systemic responses in the immune system.