A Definition of Innate Immunity
Innate immunity refers to the body’s natural immunity which is present at birth. It’s a built-in defense system that differs from adaptive immunity in that it doesn’t have to be “learned” through exposure to foreign invaders. Both innate and adaptive (or acquired) immunity are crucial for overall health and together comprise the two primary types of defenses that make up the immune system. The innate immune system consists of the skin, chemicals in the blood, and innate immune cells that are activated by specific chemical properties of certain antigens.
Thinking of the immune system as being comprised as these two main types of immune defense is perhaps too simplistic, as the immune system is far more complex and advanced than this concept alone can convey. Nonetheless, it’s important to understand how the two types work and how they differ in order to understand the immune system’s complex functionality.
How Innate Immunity Works
The innate immune system is comprised of cells and proteins that are always present in the body and ready to mount a defense against perceived threats. Unlike adaptive immunity, innate immunity does not recall previous encounters with foreign invaders or even specific antigens, so while it is ready to protect the body from a limited number of pre-recognized antigens, it doesn’t offer the same protection against future infections that adaptive immunity is capable of.
There are several types of white blood cells that make up the innate immune system, each with a different function:
- Monocytes – These cells become macrophages when they move to the tissues (from the blood stream) when an infection occurs. After moving to an infection site, monocytes enlarge and produce enzyme-filled granules that help to kill and digest foreign bacteria and cells. Macrophages also secrete a substance that attracts other white blood cells to an infection site and help T-cells recognize foreign invaders. Macrophages are also an important part of the acquired immune system.
- Neutrophils – The most common type of white blood cell in the blood stream, neutrophils are phagocytes, a type of cell that ingests foreign cells and bacteria. They also contain granules, which release enzymes that aid in the destruction of foreign invaders. Neutrophils also work in other ways to bolster the body’s defenses. For instance, they release substances that produce fibers that can trap bacteria, making them easier for immune cells to destroy.
- Eosinophils – These cells ingest bacteria but also contain enzyme-releasing granules that target bacteria that are too large to ingest, putting holes in their membranes. One of eosinophils’ primary roles is to identify, attach to, and destroy parasites.
- Basophils – These cells contain histamine-containing granules, and when they encounter allergens, they release histamine to increase blood flow to damaged tissues, which results in the inflammation and swelling that occurs as part of the allergic response.
- Natural killer cells – These cells recognize and attach to cancer cells or infected cells, releasing enzymes and other substances to damage the membranes of harmful cells.
But the innate immune system isn’t comprised of white blood cells alone. Other components of innate immunity include:
- Mast cells – These cells are found in the tissues and release histamine and other substances when they encounter allergens in the body.
- Cytokines – The “messengers of the immune system,” cytokines are produced by other white blood cells when antigens are detected. They attract other white blood cells to infection sites and also help to make fighter cells more effective at destroying bacteria and other harmful cells.
- The complement system – This system is comprised by more than 30 types of proteins that activate one another in a chain-reaction sequence known as the complement cascade. These proteins are involved in killing bacteria, attaching to them to make it easier for other immune cells to destroy them, and other functions. The complement system serves a role in both innate and adaptive immunity.
Innate Immunity vs. Adaptive Immunity
Innate immunity is particularly important because it exists at birth, offering infants some level of protection against foreign invaders and harmful substances before the body’s acquired immune system has an opportunity for exposure to antigens. However, the innate immune system only identifies certain antigens and is incapable of the adaptation that acquired immunity provides. Both innate and adaptive immunity are essential for health and well-being, combining built-in protection against some threats to an individual’s health as well as the ability to learn, adapt to, and proactively protect the body from repeated infections.
Adaptive immunity is more complex, building armies of white blood cells designed specifically to target an identified threat — a specific antigen — and after being exposed to and launching a defense against an antigen, future immune responses against the same type of threat are more efficient.
Just because it’s present at birth doesn’t mean that you can’t influence innate immunity. In fact, research shows that probiotics and other sound wellness practices can enhance innate immunity. A well-balanced diet, regular exercise, and adequate sleep will also help to bolster the body’s innate immunity, while probiotics can help to maintain the ideal balance of healthy bacteria in the gut — where the majority of the body’s immune cells thrive.