This Is How Your Body Fights the Flu

How the Body Fights the Flu

• Infection begins: Flu viruses in inhaled droplets enter the respiratory tract and infect cells. They use the cells’ machinery to make copies; within about eight hours, an infected cell may release thousands of viruses.
• Innate immune response: Infected cells release interferons, which warn nearby cells and help them resist infection. Macrophages and neutrophils engulf viruses and debris, while natural killer cells kill infected cells.
• Why symptoms occur: Immune cells release cytokines, which contribute to many flu symptoms. Cytokines signal the hypothalamus to raise the body’s temperature set point, causing shivering and fever. They also contribute to muscle aches, fatigue, and loss of appetite. Inflammation increases mucus, while coughing and sneezing help clear the respiratory tract.
• Adaptive immune response: Dendritic cells carry virus particles to lymph nodes, where matching T cells and B cells multiply. This process takes several days.
  • Killer T cells travel to infected tissue and destroy infected cells.
  • B cells become plasma cells and produce antibodies, which bind to the virus and help prevent it from infecting new cells.
• Recovery and immune memory: The virus usually declines substantially after about a week to ten days, though coughing may persist while the respiratory lining heals. Memory cells remain and can respond more quickly if the same virus returns.
• Why vaccination is updated: Flu viruses can change their surface proteins, making them less recognizable to existing immune memory. Seasonal vaccines expose the immune system to an updated version in advance.

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