Immune System Overview

The immune system is crucial for defending the body against foreign agents, such as viruses and bacteria.
Two main types of immunity: acquired immunity and innate immunity.

Acquired immunity develops over time through exposure to pathogens.
Not present at birth; it matures as the body encounters various foreign agents, such as viruses (e.g., flu virus) and bacteria (e.g., strep).
Important during COVID, highlighting the need for hospitals to manage high levels of infections due to inadequate immunity at birth.
Learning Process: The body remembers previous infections, allowing for stronger responses to subsequent exposures.

Innate immunity is the body’s first line of defense against pathogens and is present at birth.
Provides external protection:
- Physical barriers, such as skin and mucous membranes, prevent pathogens from entering vital organs.
Provides internal protection:
- Specialized immune cells: phagocytes, natural killer cells, neutrophils, etc.
- Each cell type has a distinct function in targeting and eliminating harmful cells.

Phagocytes: Cells that engulf and digest foreign particles.
Natural Killer Cells: Target and destroy infected or cancerous cells.
Neutrophils: A type of white blood cell that responds rapidly to sites of infection.

Part of innate immunity; helps detect and tag foreign bodies.
Function:
- Identifies bacteria and other pathogens by marking them with protein tags (red flags) that signal for destruction.
- Operates by damaging the membrane of the target cells, causing them to lose integrity and subsequently die.
Mechanism:
- A complement protein binds to the foreign agent. As it flows through the bloodstream, it accumulates more proteins, leading to membrane damage and eventual cellular destruction.
Primary role is to coordinate the immune response by signaling phagocytes and other immune cells to attack tagged pathogens.

Key cells: Phagocytes (macrophages and neutrophils) are essential for directly attacking and eliminating invaders.

Understanding both types of immunity is vital for appreciating how the body defends itself against diseases.
Recognizing the roles of specific cells and systems within the immune system can help understand broader health implications.