What is an important mechanism white blood cells use to kill bacteria fungi and other invading pathogens?

One important mechanism white blood cells use to kill bacteria, fungi, and other invading pathogens is called phagocytosis. Phagocytosis is the process by which white blood cells engulf and destroy foreign particles, including pathogens. Here's an overview of the process of phagocytosis:

1. Recognition: White blood cells, particularly neutrophils and macrophages, are able to recognize and bind to the surface of pathogens through receptors on their cell membranes. These receptors can detect specific molecules or patterns associated with pathogens, such as bacterial cell wall components or fungal cell wall polysaccharides.

2. Engulfment: Once the pathogen is recognized, the white blood cell extends its cell membrane around the pathogen, forming a phagocytic cup. The edges of the phagocytic cup then fuse, enclosing the pathogen within a membrane-bound compartment called a phagosome.

3. Phagosome-Lysosome Fusion: The phagosome containing the engulfed pathogen fuses with a lysosome, which is a membrane-bound organelle containing digestive enzymes and antimicrobial substances. The fusion of the phagosome and lysosome results in the formation of a phagolysosome.

4. Digestion and Killing: Inside the phagolysosome, the pathogen is exposed to a variety of digestive enzymes, antimicrobial peptides, and reactive oxygen species (ROS). These substances work together to break down and destroy the pathogen. Enzymes such as proteases, lipases, and nucleases degrade the pathogen's proteins, lipids, and nucleic acids. ROS, such as superoxide and hydrogen peroxide, can damage the pathogen's cell membrane and DNA.

5. Elimination: Once the pathogen is digested and killed, the remaining waste material is either expelled from the white blood cell or degraded further within the cell. The white blood cell can then continue to patrol the body and search for other pathogens to phagocytose and destroy.

Phagocytosis is a critical mechanism of immune defense, as it allows white blood cells to effectively eliminate bacteria, fungi, and other pathogens that invade the body. It is part of the innate immune response, which provides immediate protection against infections before the adaptive immune response can mount a specific immune attack against the invading pathogens.