Innate Immunity

The immune system is the result of an evolutionary process based on primitive structures. This includes a large number of cells, molecules, and mechanisms.

The fastest and oldest cells and responses to microbes is known as innate immunity.

The name is due to the fact that it involves recognition and response mechanisms, which are inherited and ready to function rapidly.

Read on to learn what innate immunity is and how it works as the first line of defenses.

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What is innate immunity and what is its role?

Innate immunity (also called natural or native immunity) is the set of molecules and cells that respond almost immediately to the presence of damaged microbes and cells.

This system has a defined and limited recognition pattern, selected throughout the evolution of the species and that is not modified by repeated contact with the pathogen (virus or bacteria).

The main function of innate immunity is to defend against germs in the first hours or days after an infection.

Other functions of innate immunity cells are: to act as sentinels, to block the entry of microbes and to activate adaptive immunity .

Components of the innate immune system

The components of innate immunity reflect its specificity. They can recognize molecules shared by groups of microbes and molecules produced by damaged host cells.

The main components of innate immunity are:

1. Physical and chemical barriers

This category includes skin, mucosal epithelia, and antimicrobial molecules. Its main function is to block microbes and prevent them from entering the body.

2. Phagocytic cells

These types of cells are capable of ingesting microbes or foreign molecules and then destroying them. Some examples of phagocytic cells are: macrophages, dendritic cells, NK cells, and neutrophils . (The latter are the star effectors of innate immunity).

3. Blood proteins

The main component proteins of innate immunity are the members of the complement system, the pentraxins and the ficolins. These are important both to neutralize, and to signal and mark microbes in order to optimize and amplify the immune response.

How does the innate immune system work?

When a pathogen enters the body, it generates danger signals capable of activating innate immunity. These are the so-called PAMPS and DAMPS.

So the innate immune response can fight microbes through two main reactions:

1. By inflammation

After the entry of an infectious agent into the tissues, changes can develop in the blood vessels that increase their permeability. This is an innate response known as inflammation.

This enables large numbers of innate cells to be recruited at the site of infection to engulf microbes. Inflammation is a fundamental tool to amplify the immune response.

2. Inhibiting virus replication

The innate immune system can block viral infections by expressing type 1 interferons .

As the word suggests, interferons are a family of cytokines capable of interfering in the viral cycle. These molecules can activate genes capable of generating rapid changes to block viral transcription and replication.

Note: All innate immune responses are regulated by negative feedback mechanisms that limit possible damage to self tissues.

Why is innate immunity so important in fighting an infection?

Innate immunity is important to fight an infection because it is not only responsible for acting quickly and first, but it also plays a fundamental role as an activator of adaptive immunity.

In most cases, innate immunity is sufficient to fight infection. However, these mechanisms also lead to the production of molecules that stimulate adaptive immunity.

Without innate immunity, our body would not be able to produce inflammation and orchestrate the rest of the molecules that exist to combat and prevent possible damage from infectious agents.


Innate immunity is the set of molecules, cells and mechanisms whose function is to give a rapid response to an infection.

The innate immune system is the oldest evolutionarily, but that does not stop being specific. Its activation signals are the PAMPS and DAMPS.

The components of innate immunity are: chemical barriers, phagocytic cells and proteins that circulate in the blood.

The two main mechanisms of the innate immune system are the induction of inflammation and the inhibition of virus replication by type 1 interferons.

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