Understanding the Flu and the Immune Response

Common Flu Symptoms

• Begins with a tickle in the throat, leading to a cough.
• Muscle aches, irritability, and loss of appetite.
• Often attributed to the infection itself, but largely due to the body's immune response.

Initial Response to Infection

• Pathogen Entry: Begins when pathogens like the flu virus infect and kill cells.
• Immune System Activation: The presence of the virus alerts the immune system.
• Macrophages Role:
  • First responders that search for and destroy viruses and infected cells.
  • Release cytokines to recruit more immune cells.

Escalation of Immune Response

• Spread of Virus: Sometimes viruses spread to blood and vital organs.
• Coordinated Attack: Immune system coordinates stronger responses with the brain.

Symptoms and Their Role

• Cytokines and Vagus Nerve: Triggers two responses:
  • Vagus nerve transmits information to the brain stem.
  • Cytokines travel to the hypothalamus.
• Hypothalamus Response:
  • Produces prostaglandin E2.
  • Increases body temperature, sleepiness, and decreases appetite and thirst.

The Purpose of Symptoms

• Theories on Benefits:
  • Temperature rise may slow bacteria and aid immune system.
  • Sleep aids energy conservation for fighting infection.
  • Reduced iron intake starves bacteria needing iron.
  • Reduced thirst limits pathogen transmission via bodily fluids.
  • Aches highlight worsening conditions or infections.

Psychological Effects

• Cytokines and prostaglandins affect brain neurotransmitters.
• Impact areas:
  • Limbic System: Emotions.
  • Cerebral Cortex: Reasoning.
• Can cause irritability, sadness, and confusion.

Immune System Imperfections

• Autoimmune Diseases: Immune system mistakenly attacks the body.
• Evolutionary Balance: For most, the immune system is finely tuned over millions of years to protect rather than harm us.
• Symptoms as a Protective Mechanism: Annoying but a necessary part of the immune defense system.