1. Detection and Recruitment:
* Phagocytes (neutrophils, macrophages): These cells act as the first line of defense. They roam the bloodstream and tissues, constantly searching for invaders. They detect microbes through specialized receptors on their surface, recognizing patterns unique to pathogens.
* Signals: Upon detection, these phagocytes release chemical signals (cytokines) that alert other immune cells and trigger inflammation.
2. Inflammation:
* Blood vessel dilation: The signals from phagocytes cause blood vessels in the affected area to dilate, increasing blood flow and bringing more white blood cells to the site.
* Increased permeability: The blood vessel walls become more permeable, allowing fluids and white blood cells to leak into the tissues, leading to swelling and redness.
* Pain: Inflammation also triggers nerve signals, resulting in pain, a warning sign that something is wrong.
3. Attack and Destruction:
* Phagocytosis: Phagocytes engulf and destroy microbes directly, breaking them down with enzymes.
* Natural Killer (NK) cells: These cells identify and kill infected cells or abnormal cells, such as cancer cells, before they can spread.
* T cells (cytotoxic T cells): These cells target specific infected cells, releasing toxic substances to destroy them.
4. Antigen Presentation:
* Macrophages and dendritic cells: These cells, after engulfing microbes, break them down and present fragments of the microbe (antigens) on their surface. This process alerts the adaptive immune system.
5. Adaptive Immune Response:
* T cells and B cells: The presentation of antigens activates specific T cells and B cells that are programmed to recognize and fight that particular microbe.
* Antibodies: B cells produce antibodies that specifically bind to the microbe, marking it for destruction by other immune cells.
* Memory cells: Some T cells and B cells become memory cells, enabling the immune system to quickly and effectively fight off the same microbe in the future.
In summary: When microbes enter your body, your white blood cells act as a multi-layered defense system, detecting, recruiting, attacking, and remembering the invaders to protect you from future infections.
