10 Examples of Innate Immunity | Their Composition and Action

Innate immunity is a part of the immune system that exists from an individual’s birth. The examples include

1. Physical barriers: Skin and Mucous Membrane
2. Physiological barriers: Saliva, HCl in the stomach, Tears in the eye, Sweat.
3. Cellular barriers: Neutrophils, Monocytes (Macrophages) and Lymphocytes.
4. Cytokine barriers: Interferons, interleukins, lymphokines, & TNF

Innate immunity is also called natural immunity, as it is an essential method of defense.

It comprises 4 basic types active throughout the individual’s life.

It saves us from infectious attacks in almost every moment of life.

Examples of Innate Immunity

Physical barriers

This includes skin and mucous membranes. These are nonspecific types of immunity

Skin

• It covers all the visible parts of the body and provides a mechanical barrier for pathogens or other invading microbes by covering body surfaces.

• It is thick, hard, and keratinized, making it tough for any microbes to enter the body.

• If a wound or cut exposes the internal tissues, there is a chance of an immediate attack of microbes on the injury.

• Hence, we will notice pus formation and other secretions that fight infectious bacteria and other microbes from entering the body.

• This lasts until the injury is covered by new skin tissue (or scar) during the healing process.

• This pus is formed due to the rush of white blood cells to arrest the area from infection and enhance the speed of healing.

Mucous layer

• This is another physical barrier; unlike skin, it is a coating that lines the inner surfaces.

• This includes the digestive tract, intestine, respiratory system, and mouth, which are frequently exposed to air, food, and water from external sources.

• Mucous, unlike skin, is a moist, smooth cover that can be shed frequently and formed again.

• This moisture and thickness enable the removal of any microbes from the body.

• Further, the epithelial cells in the inner lining of the trachea of the respiratory system have cilia.

• These cilia have a unidirectional movement and entrap any dust or other particles from the outside air.

• These trapped materials are expelled along with phlegm.

So physical barriers like skin and mucous are examples of innate immunity.

Physiological barriers and Chemical barriers

As the name implies, these are the ones that are released as a part of the body’s regular physiology.

These include

The chemical barriers

1. Saliva is the mouth
2. Hydrochloric acid in the stomach
3. Tears in eyes.

Physiological processes like

1. pH
2. Temperature (fever)
3. Peristalsis.

These three secretions prevent microbes from gaining entry into the body.

Saliva is secreted by the salivary glands in the mouth to keep it moist.

• This saliva has a metabolic enzyme lysozyme in it.

• This enzyme helps kill the microbes in the buccal cavity while chewing the food.

• Since the food first enters the mouth, the destruction of pathogens here limits the movement of pathogens into the body.

Hydrochloric acid is released in the stomach by the parietal cells.

• This hydrochloric acid keeps the pH of the gastric environment at 1.5.

• This highly acidic pH leads to the degradation of protein in food as well as microbes.

• Thus, many microbes are killed in the process and prevent the chances of infection from food.

Tear in the eyes:

• Eyes are moist organs directly exposed to the environment.

• So, the chances of infection to the eyes are very high.

• However, the secretion of tears helps to keep these pathogens away.

Tears in the eyes have many antimicrobial substances like the

1. Enzymes lysozyme
2. Lactoferrin
3. Lipocalin
4. Secretory immunoglobulin A (IgA) 
5. Enzyme secretory phospholipase A2
6. Secretory leukocyte protease inhibitor

which helps kill the microbes trying to attach to the eye surface.

• Besides, a few cationic antimicrobial peptides and surfactant proteins help destroy the microorganisms that enter the body through the eye.

Physiological factors

• pH, like an acidic environment in an area like the genital tract, minimizes the growth of microbes.

• High temperature (fever): in case of infection, the monocytes release interleukins that can raise body temperature. The intention is to provide an unfavorable environment to limit the multiplication of pathogens inside the body.
• Peristalsis is the movement of the gut. It can remove pathogens from the gut either through diarrhea or vomiting.

Cellular barriers

These are the immune cells in the body that kill any pathogen roaming inside the body.

These include three white blood cells viz.

• Neutrophils
• Monocytes and
• Lymphocytes.

• Neutrophils are granulocyte types of white blood cells and are high in concentration of all three. 

• They attack pathogens like bacteria and protozoa, which move in the blood and eat them (phagocytosis).

• So, they are meant to clear any pathogens from blood circulation.

Monocytes

• These are the granulocytic white blood cells.

• They act as the second line of defense in the body.

• They convert into macrophages once they enter the tissues. These macrophages keep moving throughout body tissues.

• When they encounter foreign pathogens, they engulf (cell-eating) them.

• These foreign microbes inside the macrophages are destroyed with the help of lysosomes.

Lymphocytes

• These cells recognize the pathogenic microorganisms and produce antibodies against them.

• These antibodies bind to the pathogenic cells and their toxins, neutralizing them.

• Thus, this cellular barrier kills foreign pathogens and safeguards the body.

Cytokine barriers

These are pertinacious substances secreted by body cells to keep viruses and other pathogens at bay.

When a virus infects our body cells, the infected cells produce interferons, a kind of cytokine that alerts the neighboring cells.

There are three types of interferons:

1. Interferon-α,
2. Interferon-β, and
3. Interferon-γ.

When interferons are released, they bind to the surface of other cells and signal them to produce protein to defend against viral infection and replication.

Besides, there are also other cytokines, like interleukins and chemokines, which also play a role in the immune system.

Innate Immunity Quiz – Test Your Knowledge on Natural Defenses

References:

• Parts of the Immune System
• Immunology at the Skin Barrier
• How the skin’s immune system cells coordinate defense against threats
• Antimicrobial Compounds in Tears
• Human antimicrobial peptides in ocular surface defense