Innate immunity is the first line of defense against invading pathogens and other foreign substances. It is a non-specific, rapid response system that is present from birth and does not require prior exposure to the pathogen. Innate immunity works by recognizing and responding to common patterns present on a wide range of pathogens, such as bacterial cell walls and viral nucleic acids.
The components of innate immunity include physical and chemical barriers, as well as a variety of specialized cells and molecules:
- Physical barriers: The skin and mucous membranes of the body provide a physical barrier that prevents pathogens from entering the body. In addition, the cilia in the respiratory tract trap and remove pathogens.
- Chemical barriers: The body produces a variety of chemicals, such as stomach acid, tears, and saliva, that are toxic to many pathogens and help to prevent infections.
- Phagocytic cells: Phagocytes, such as neutrophils, macrophages, and dendritic cells, are specialized cells that engulf and destroy invading pathogens.
- Natural killer cells (NK cells): NK cells are specialized immune cells that recognize and destroy infected cells and cancer cells.
- Complement system: The complement system is a group of proteins that work together to destroy invading pathogens. The complement system can be activated through three pathways: the classical pathway, the lectin pathway, and the alternative pathway.
- Cytokines: Cytokines are small signaling molecules that are produced by immune cells and play a role in activating and coordinating the immune response.
Innate immunity is able to respond rapidly to invading pathogens, but it is not always able to eliminate the pathogen completely. In cases where the pathogen is not eliminated by the innate immune response, the adaptive immune response is activated. The adaptive immune response is a slower, more specific response that is able to target specific pathogens and produce memory cells that provide long-term immunity.
Disruptions in innate immunity can lead to a variety of immune disorders, such as autoimmune diseases and immunodeficiencies. Deficiencies in innate immunity can make individuals more susceptible to infections, particularly those caused by intracellular pathogens.